Questions on: Oak

Ron Smith, Horticulturist, NDSU Extension Service

Q: For Arbor Day this year, we purchased two white oak trees from the city. We planted them about two months ago, but they have not sprouted a single leaf. The branches are flexible and do not break off when we test them. Are the trees still in shock or did they not survive the transplant? (e-mail reference)

A: Scrap the bark off some of the branches with your thumbnail to see if the cambial tissue is green underneath. If it is, there is a slight chance the trees will break bud. If what is underneath is any other color, they are finished.

Q: If we remove our oak tree and stump, will the suckers that are all over our yard remain or will they die? (e-mail reference)

A: It depends. If you continually mow them off, they eventually will die. Left alone, some could develop into trees again, depending on environmental factors. They easily can be controlled with regular applications of a broadleaf herbicide that contains dicamba.

Q: I was hoping that you could answer a question for me. I live in Florida and transplanted an oak tree to my yard. There were small buds just starting to form when we transplanted, but now they are dead and crunchy. I have trimmed back some of the branches to encourage survival. There is new growth, but only three new branches are starting to form at the base of the tree. What should I do? Is the tree doomed to die? Thank you. (e-mail reference)

A: Oak trees do not transplant very well. It sounds as if your attempt is re-enforcing that perception. Not knowing what kind of oak you are attempting to grow, I would have to guess that the chances of this one making a decent tree are slim. You probably would be better off taking it out and starting with a fresh tree from a local garden center.

Q: I am from Fargo, but now live in the St. Cloud area. I bought a home that was built in 2003. The developers did a great job of keeping 14 white oaks in the yard. Most of the trees are 60 to 80 feet tall. There is one tree in the front yard that has a huge canopy, but looks to be mostly dead. It is fairly close to the house and the sidewalk is less than 4 feet from the trunk. I have had several landscape professionals stop by to give me quotes on trimming the trees. Only one has said that the front yard tree is probably gone. He sounded the most knowledgeable, but I want to do everything I can to save this tree. There looks to be some buds forming near the top. Is there anything I can do in the way of fertilizer or anything else for this tree? I would rather not top it. Any help would be much appreciated. (Rogers, Minn.)

A: You need to talk to an International Society of Arboriculture certified arborist in your area. The Ludivig Tree Service is in your area and can be reached at (320) 267-6629. Never accept any work from an individual who says he will "top" the tree. All that does is create a huge Frankenstein-looking tree and eventually leads to the tree's death. The certified arborist should be able to tell you what, if anything, can be done to save the tree or whether you should have it removed to keep it from becoming a hazard.

Q: I have a pin oak that was damaged by repeated spraying with a water sprinkler. The bark is peeling off and the wood is rotted on the damaged side. The tree looks healthy otherwise. Can I do anything to save this tree or should I cut it down? I would like to save the tree. (e-mail reference)

A: The best advice I can give you is to seek out the assistance of a certified arborist in your community. Tell the arborist up front that you would like to have the tree saved if possible. It is too easy and fast to cut down a tree. If the tree doesn't pose a hazard, then every effort should be made to save it.

Q: We live in Aurora, Ill. We have a large 15-year-old Linden oak in our back yard situated about 30 feet from the house. It is a very nice tree. Our son brought it home as an Arbor Day planting and it has grown well ever since. This fall we began seeing some of the small branches begin to lose bark. I'd say about 10 to 15 of the smaller branches are impacted. I have seen squirrels nibbling on the hanging bark and originally thought that they might be the cause, but squirrels have been in this tree all along, but the symptoms have just appeared this year. Perhaps you have some suggestions on what may be happening to our tree. Thanks very much for your help. (e-mail reference)

A: This sounds very much like normal self-pruning of the tree. As the density of the tree's canopy continues to increase, some of the lower branches will die off as you describe. I am, of course, only making an educated guess. I would suggest contacting an International Society of Arboriculture-certified arborist in your community to evaluate the tree. Go to to locate an arborist. Be sure to check the person’s credentials and ask for references before allowing any work to be carried out on the tree.

Q: We live in Pembina County. Five years ago, we planted 25 bur oak trees that are growing well. However, there is one tree that leafs out with a burgundy-red color. I have not been able to find out why or what species of oak tree it is. Can you tell me what this is? (e-mail reference)

A: A genetic aberration that may or may not have significance in the nursery business. Keep track of it during the next few years. If it continues to behave this way, get back in touch with me because our woody plant researcher is always interested in new variations of trees.

Q: I have lots of black oak trees. When the wind blows fairly strongly, small clumps of leaves from the end of the branches break off and litter the yard. The branches are hollow, so I cut a branch to inspect it and found a worm inside. What type of worm is this and can I do anything to prevent the problem? (Berwick, N.D.)

A: This is a stem borer problem, but I cannot say what type of borer it is without an examination. Get some Advanced Tree and Shrub Insect Control. It is a systemic that will kill any further intruders, such as the one you described. The material is available at local garden stores.

Q: I have an oak that is dropping little, beige/yellow balls that look like tiny seeds. Sometimes (I swear) the little balls are jumping. We are fighting gypsy moths with this tree (we lost three ash trees last year to ash bore) and I don't want to take a chance on losing any more trees. I have five other oak trees in front of the house, but they donít have (or I can't see) these tiny seeds. Please tell if I need to do something. Thanks for your time and information. I appreciate it. (e-mail reference)

A: What you are probably witnessing are acorns infested with acorn weevil larvae. Insecticides may or may not be useful at this stage. I suggest getting an International Society of Arboriculture arborist out to examine the trees to see what action can be taken to bring this and the other pests under control.

Q: I have two red oak trees that were planted last spring. They only are a few feet tall, but are nicely leafed out. I am concerned about the fact that the leaves are turning a very yellow-green color, especially on one tree. The leaves are not curled. There are some signs of insect feeding on the leaves, but it is very minimal. The leaves look healthy, but I thought oak tree leaves were supposed to be a dark color. I'm hoping there isn't a problem with these trees. Any ideas? (e-mail reference)

A: This could be a reaction to a high pH level, which would tie up available nutrients, especially iron. I would suggest fertilizing with something, such as Miracid or Miracle-Gro, to see if this helps correct the problem. Also, the tree may be planted too deeply or the roots are in a poor-draining soil that remains wet for extended periods. It also could be that root rot has set in.

Q: I have an oak tree at my home in Ottertail, Minn. It has little, brown balls in clusters on its branches. Dean's Landscaping in Wahpeton, N.D., told me the brown balls are made by tiny wasps that wonít damage the tree. Do you have any ideas? (e-mail reference)

A: Listen to Dean's Landscaping! It is telling the truth and you have nothing to worry about.

Q: The oak tree in our garden was cut down by accident. I collected lots of acorns from it, although many are not in good shape. Iím very eager to grow some of them, but Iím not very knowledgeable about how to do it. Could you give me some simple steps on how to grow the acorns? (e-mail reference)

A: If the intent is to use acorns for propagation purposes, then gather the acorns as soon as possible after they drop from the tree because mold sometimes can infect fallen acorns, which destroys the cotyledons within. There is a difference in oaks as to germination approaches. The white oak (ones with rounded leaf lobes) groupís acorns will germinate shortly after falling, so that is another reason for the rush in collecting the acorns and putting them in cold storage until planting. The red or black oak group needs cold stratification in moist sand for about 90 days to facilitate germination. The first thing you need to do is test the acorns you have collected for soundness. Fill a bucket or sink with water and dump in the acorns. Get rid of the acorns that float. The acorns that sink are the soundest seeds to use for growing. Without knowing what type of oak you are referring to, all I can suggest is that you plant some of the acorns that sink in water as soon as the frost is out of the ground to see if germination will occur. Store the rest of the acorns in the crisper of your refrigerator for 90 days in damp sphagnum moss to see if the root radicle starts to emerge from some of the acorns. If the roots start to emerge, get them planted immediately. Squirrels will be interested in what you are doing, so be sure to protect the new seedlings with chicken wire or something similar.

Q: Could you tell me how far away I should plant an oak tree from a water line? (e-mail reference)

A: If the water line doesn't leak, you don't have to worry about where to plant it. Just don't hit the line with your shovel or backhoe. If the line is leaking, then plant the tree as far away as possible.

Q: My oak tree leaves have brown spots. Is this a fungus? Can it be treated and with what? Maybe it is from the wet spring we had. Thanks and I enjoy your column. (Portland, N.D.)

A: It could be a fungal disease brought on by the wet weather. I would suggest getting a sample to the plant diagnosis lab at Waldron Hall on the NDSU campus as soon as possible for analysis and recommendations for control. Thanks for the nice comments about the column!

Q: How can I repair a large area of bark stripped off an old oak tree? (e-mail reference)

A: With a sharp and probably large pocket knife. Cut back to where the bark is attached to the wood below and leave it alone from there. If the tree is otherwise healthy, it will begin healing itself by producing callus tissue that will roll over the open, stripped area in the next few years. Trees have better defensive mechanisms than most people realize. With their good intentions and wrong action, folks often slow or totally inhibit the proper healing of their trees.

Q: We have a burr oak tree. Last year some small ďballsĒ appeared on it and the new leaves started to curl. We sprayed with Diazinon, which seemed to help, but the balls started again this year. Some are the size of chokecherries and some about an inch in diameter. The inside seems to be fibrous and very lightweight. What are they and is my tree doomed? (Clearbrook, Minn.)

A: There is nothing to worry about! Oaks are prone to getting galls growing on their leaves, petioles and branches. They do not hurt the tree, but do provide some ornamentation for you to enjoy. Some people make a hobby of collecting oak and other gall formations.

Q: I have an oak tree (not sure what kind) in my front yard. At the base of the tree, shoots are coming up. It looks like it might be new shoots from acorns dropped or else it is coming from the base of the tree under the ground. Is it safe to cut these back? If so, is there a better time of year to do that? (e-mail reference)

A: The shoots probably are suckers. Cut them off anytime they show up to keep the tree growing vigorously.

Q: I recently bought an old house that has a beautiful, young oak tree. The tree is about 4 1/2 feet from the foundation. I am assuming that this is too close to the foundation, but I wanted to ask someone before cutting the tree down. (e-mail reference)

A: That distance should not be a problem if you have a sound foundation. If the foundation is cracked and leaking, it will pose a problem. I hate to see a tree cut down that has the potential that an oak has! Try contacting someone locally, such as an arborist or a member of the International Society of Arboriculture, to check on the feasibility of digging up the tree and replanting it in a better location. With a tree that close to the house, the branches definitely would become a problem with the windows and roof shingles, so it should be moved if possible.

Q: I have several burr oaks I would like to move. I have heard they have a long taproot, so cutting it off would kill the tree. Is this true? (e-mail reference)

A: Moving mature oaks gets more difficult with age. If you are going to move them, I would suggest doing so with a tree spade early in the spring and before leaf-out. In all probability, you have some loss, but that should not keep you from attempting to save them

Q: How often does oak tree bark regenerate? The tannins in oak bark are used for vegetable tanning of leathers and for medicinal purposes. If a tree is exposed to environmental contaminants, wouldnít the tannins extracted from the tree contain some of these contaminants? If so, at what point is new, clean bark regenerated? (e-mail reference)

A: The bark continuously is renewed from the cambium. Essentially water proof, (remember it is used in corking wine) contaminants are limited to the outer surface of the bark. Bark regeneration surges in the spring along with other plant growth. As to the tannin contamination, I would assume it is checked to be sure any contamination is below threshold levels. I am not qualified to answer that question, so I suggest you contact the agencies that use such products.

Q: We have several mature oak trees that are 30 to 40 years old. This past weekend we noticed many woodpecker holes. We purchased this place last summer and occasionally saw woodpeckers and a few old holes. The holes we are seeing are new and quite large. What can we do to prevent more damage? (Battle Lake, Minn.)

A: Oaks and other tree species have evolved over the eons with woodpeckers and sapsuckers, a type of woodpecker. Both obviously have survived and thrived! I know that isnít what you want to hear, but there are ways to control the birdís activity. If they habitually are going to the same area on the tree, you can spread Tanglefoot over the area. This will discourage them because they dislike getting their feet sticky. You can hang old aluminum pie tins in the trees or aluminum strips that move in the wind. This tends to frighten them. If you see them in the tree, a sudden loud noise will move them out of the tree. This has to be repeated to be effective. Shooting them is not an option. This species is protected under the Wildlife Protection Act and can result in a hefty fine if you are caught shooting them. You also want to check the holes carefully. If they appear to be going around the tree trunk, then it is probably a sapsucker and the damage should not be anything to worry about on mature oaks. They will seal up with spring growth. If the holes appear to be random, check to be sure you donít have bark beetles. If you do, the hole would be D-shaped.

Q: We purchased a home with a large pin oak in front. We have noticed some of the lower branches are growing horizontally and then reach up to get the sunlight. Is this putting too much stress on the tree? Should we consider trimming these branches? (e-mail reference)

A: What you are seeing is normal pin oak growth. If it will make you feel better pruning off the lower branches, then do so. It wonít make a difference to the tree. I assure you it isnít struggling to get to the sunlight.

Q: During recent construction, a backhoe scraped and scared my beautiful oak tree. I have heard several opinions about what I needed to do to save the tree. The scrape is about 18 by 10 inches and just affects the bark. (e-mail reference)

A: If the damage doesnít girdle the trunk, the tree likely will survive. Take a sharp pruning knife and clean up the wounded area. Cut off all the remaining loose bark. Donít apply a wound dressing because it inhibits further healing.

Q: My friend has a young pin oak, which she grew from a very small sapling. This year a vertical indentation, approximately an inch and a half wide, appeared in the trunk. The indentation starts 6 inches above the ground and extends to about a foot and a half up the tree. In the indentation there are three small patches of what looks like dead wood. She said the area was soft when it was noticed, but is now hard. The tree looks healthy, but the patches within the indentation stand out in an otherwise healthy looking trunk. Except for the dark exposed wood patches, the bark within the indentation is intact. (e-mail reference)

A: It is probably the treeís reaction to a physical injury at some time. The tree is compartmentalizing the wound with callus tissue. The tree should be fine, but monitor it for another year or so.

Q: Can you provide any clue on the green circular patches that are growing on my red oak? Is it a fungus or anything I have to worry about?

A: It is probably moss or algae growing on the trunk, usually on the north or east side, but not always. It is harmless, so there is nothing to worry about.

Q: My husband and I built a house in the spring of 2000. There is a wonderful burr oak about 20 feet from the back of the house. There has been no further construction and the tree has been in perfect health (from what I can tell) until this spring. Last year's dried leaves still remain on some branches and it did not bud. I see a woodpecker from time to time and when construction started there were a couple of large branches cut off that were facing the house. Is there anything I can do to save it? (Hugo, Minn.)

A: Check around the base of the trunk. It would be good if there is a flair on all sides. If it has a pole appearance going into the ground, not good. The fact that the leaves are still on the tree from last year means it did not go completely into dormancy. In either case, it sounds like it could be dead. I can't help but be suspicious of the contractor's activity around the tree during the construction of your home. Contact Gary Johnson at the UMN Urban Forestry Department. He is an arborist and probably knows his stuff better than anyone else in North America. At the very least, have the tree evaluated as to the cause of death, how sound it is and how quickly it needs to be removed to eliminate any hazard potential. Removing the tree may devalue your property somewhat. Gary can assign the value lost. I'm sure that if Gary is too tied up right now, he can recommend someone equally competent.

Q: We have a large, I think, white oak tree in our front yard. About a year ago, we thought lightning struck it. Not long after, the bark started to peel off. It did not grow leaves last year, but this year it is. Do we need to cut the tree down? (E-mail reference)

A: From your description, lightening most likely did strike the tree. The initial jolt probably cooked the leaves and most of the main trunk cambium and root system. The tree is now leafing out with carbohydrate reserves in the limbs. It is very likely the leaves will be undersized and die prematurely. If this doesn't happen, and the tree leafs out normally and produces new growth, something else happened. I would advise you to have an ISA certified arborist examine the tree. This is important because of its location. It could cause extensive property damage or personal harm if it should fall.

Q: During some recent construction, a beautiful oak of mine was scraped by a back hoe. The result was about an 18- by 10-inch scar where the bark has been peeled back. What should I do to ensure that I don't loose the tree? (E-mail reference)

A: As long as the tree has not been girdled, (bark removed all the way around the tree) it will survive, with some help from you. I would contact a local International Society of Arboriculture certified arborist to examine the tree. They will likely cut back to the attached bark to facilitate healing and provide or suggest a fertilizer. You can do this yourself if you are sure you know what you are doing, but a professionally-trained eye might see other problems with your tree that you are unaware of. If the tree is important to you, it would be worth the investment.

Q: I have a large oak in my yard that has some exposed roots. I want to make a flowerbed around the tree and add some potting soil to accommodate the plants. Someone told me the tree will die if I cover the roots with soil. Is that true? (E-mail reference)

A: A four to six inch covering around the base of the tree using typical potting soil which is well-drained will not cause a problem. That amount of soil should be more than enough to grow flowers in. The nutrient or air-absorbing parts of the roots are at or beyond the drip line. You might have problems if you covered that part of the root system. Keep about three to four inches around the trunk free of soil. It helps keep disease problems from developing. You can do that easily by using poly-edging. Adjust the edging as the tree increases in caliper.

Q: I have an oak tree in my front yard that seems to be growing an odd bunch of dark green colored leaves. It reminds me of a holly plant. What should I do about it? Will it damage the tree? Iím going to have it cut out but is there any way to prevent it from returning? (E-mail reference)

A: Itís probably mistletoe not holly. Thereís not a lot you can do but it shouldnít hurt the tree. I suggest leaving it where it is. Birds eat the fruit and spread the seed which sometimes lands on an oak branch. This is a good example of a symbiotic relationship between two plants and could be a "teachable moment" for a youngster.

Q: What causes oaks to die when several feet of soil are packed around the roots and air is pushed out? (E-mail reference)

A: Thatís a good question. Oaks are especially sensitive to soil fill over their roots, with just inches, not feet of fill resulting in their death. When the air is driven out of the root zone, anaerobic conditions then exist and the free exchange of respiration gasses canít be released. The roots cannot pick up enough oxygen from the soil pores. In the absence of this oxygen, the meristematic regions of the small roots are injured because of inadequate aeration. When this occurs, alcohol, lactic acid and other incompletely oxidized substances accumulate in the roots, resulting in their eventual death. Basically, in the absence of oxygen, the terminal electron transport system cannot operate, which then results in less energy being produced, growth being reduced and finally death due to the accumulation of toxic substances. Itís like the Great Salt Lake in Utah; everything accumulates, nothing flows out. The result is something that cannot support life as we know it (great for floating things though). In nature, distribution of many species is restricted by high oxygen requirements, which exclude them from flood plains or areas where soil tends to be saturated. Those that are adapted to flooding and can tolerate backfilling to a certain degree have a stem or root system that interacts in some way to affect the gas exchange, or they are simply tolerant of anaerobic respiration.

Q: The oak tree by our garage dropped almost no acorns last year. Usually it litters the driveway. Does this have any significant meaning? I was pleased because I didn't have the big mess to clean up but I'm wondering if it's a sign the tree is unhealthy. (E-mail reference)

A: The acorns not dropping is a sign that the tree spent too much energy the previous year developing the fruit. The tree needs to build up its carbohydrate reserves again by not bearing any fruit. In some cases it may take two years. Enjoy the respite because the acorns will return.

Q: I read oak trees have long taproots that keep them from blowing over. How long are they, especially in relation to the size of the tree? Is this straight-down root unusual for a tree? I know the Bible talks about oak trees when speaking of something strong or long- lived. What sets them apart from other tree species? (E-mail reference)

A: Oaks (Quercus spp.) live a long time, are generally large trees and because of the extensive taproot system, have the distinctive characteristic of generally being quite drought hardy. The root system usually exceeds the volume of the branching system and like roots everywhere, will follow the path of least resistance and go where there is a balance of air and water. Oaks produce male and female flowers (staminate and pistillate) on the same tree in early spring. The male flowers are conspicuous and drooping while the female flowers are inconspicuous and held close to the leaf axils. From these flowers of course, arise the acorns, which are sources of food for animals. The acorns were also sources of food for Native Americans and early settlers. Oaks are divided into two distinct groups, often easily recognized by the foliage. Red oaks have sharp, bristled lobes with acorns that take two seasons to mature. White oaks have leaves that are rounded lobes, but never bristle tipped. Their acorns mature in just one growing season, making them tastier for those who choose to eat them. The bark on the red oak is dark and furrowed, while the white oak is typically grayish and scaly. That oaks are enduring and strong is without question. Oak trees can live for more than 100 years even if they are stressed by mankind's follies. Most oak species are found in the northern regions of the country.

Q: There are "balls" growing on my oak tree. What are they? (Galesburg, N.D.)

A: Your sample was of the oak bullet gall wasp known as Disholocaspis quercusmammor. Their damage is cosmetic but not lethal. No control is necessary or practical. Tiny insects known as gallflies or minute non stinging wasps will eventually attack all oaks. Both insects cause galls, gallnuts, or just plain oak balls.

Q: I need to move some honey locust and bur oak this fall. Honey locust can be moved easily. However, I do not have any experience moving bur oak and understand that they do not transplant easily. I have a Vermeer 44 and will use root fertilizer and apply mulch when transplanting. (E-mail reference)

A: A Vermeer 44 is a good-sized machine to do the job. Whitewash an "X" on the north side of the trees before moving them and make sure that "X" faces north in the new location. A little luck, in addition to what you stated, is all that I can think of for you to be successful.

Q: I planted 20 bur oak trees this spring. They were about 2 feet tall when I planted them and some have grown more than a foot. About half have grown very well, but the rest seem to be having some problems. As summer went on, some of the leaves began to turn yellow and now have dried up. The trunks of the trees still seem limber. They have all received the same amount of water. They are planted in a row about 25 feet apart. The problem trees are spread sporadically in the row. I was told they might be short of iron. If that were the case, would it not affect all of the trees? (Aberdeen, S.D.)

A: Bur oak is native to our region of the country so I doubt it would be suffering from an iron deficiency. I think what you are seeing more of is the genetic variation that exists in seedlings. I wouldnít apply anything now. Perhaps next spring, as the leaves are unfolding, you could add some chelated iron. It certainly would not hurt and is bound to improve things in most cases.

Q: We planted five bur oak seven years ago. They have not grown well. We are in the southeastern part of N.D. in heavy soil. I'm beginning to think we should replace them. What would you advise? What would be a good replacement? (E-mail reference)

A: Certainly if any tree has been in a planting site for seven years and has not grown well, one should consider replacing it. With what depends on what it is youíre looking for. Here is a short shopping list of trees that would roughly fit into the same category of your bur oak: hackberry, linden, black walnut, black locust, and common hornbeam. None grow very fast so if you are looking for that, you will have to go in an entirely different direction.

Q: Is it hard to grow little oak trees in this part of the state? My brother planted two little ones a couple of weeks ago that turned yellow and died. He got them from a guy in Grassy Butte where they were growing wild. He has been watering them and he used bark to put around them. Any ideas as to why they died? (E-mail reference)

A: Oak trees do not transplant well because of their tap root system. He is better off getting seed (acorns) and planting them where he wants the trees to grow.

Q: What can we do with an oak tree that was hit by lightning last night? The tree lost a major branch and will have a large wound when we are done trimming it. I am concerned about oak wilt because there are three or four other oaks around it. Is the tree going to die either way? (Oxbow, N.D.)

A: A tree that has been directly hit by lightening is history. It will become apparent immediately or in a very short time. All the leaves will turn brown. You might check the other oaks in anticipation of them dying as well. That will depend on whether or not root grafting has taken place between the plants. You basically have two choices. You can prune only what is needed for safety purposes and hope that your tree(s) is an exception to a lightening hit and will survive and come back next year. The other choice is to simply write the tree off and get it out of there while the getting is good.

Q: Iím trying to transplant some small oak trees that I started from acorns a few years ago. They are about 3-feet tall and have tap roots about that long. I've dug up a couple but have trouble getting all the tap roots out so I end up breaking off part of it. I usually have at least 2-feet of it intact. Will they still grow or do I need the complete root? (Tioga, N.D.)

A: You donít always need the complete root but the more you can get, the better. It also depends on the time of year. If you can move them early in the spring, before they begin leafing out, their chance of survival will be better.

Q: How old do burr oak trees have to be before they start to produce acorns? (E-mail reference)

A: I really don't know how many years it would take. It could take 5 to 10 years before the plant is mature enough to enter into a sexually reproductive stage of growth?

Q: My husband and I recently found four burr oak acorns from one of our trees. We put them into the freezer and would like to plant them. We don't know if we should take the large cap off the acorn before we plant it or which direction to place it in the ground. The tree we got them from is beautiful and healthy so hopefully the acorns will produce good trees. (E-mail reference)

A: Simply go ahead and plant them about 3-inches deep, disregarding the orientation of the acorn. If they are viable, they will sprout and grow next spring. If they arenít viable, nothing happens.

Q: I read in one of your oak questions that one should not drive on the roots of a tree or it will die in three to five years. You also stated that you can put down plywood and drive on it and be ok. Does this theory hold true for most trees? I have seen a couple of oak trees so close to the road they have put traffic warning diamonds on them to keep people from hitting them as they pass. They are just a few inches from the road with asphalt covering some of the roots. Does the asphalt keep them from being hurt? One of these trees is by a hospital and has been there for the 23 years Iíve lived in the area. Does driving on the roots (compacting the soil) matter to all trees or just some varieties. (E-mail reference)

A: Life is full of confounding anomalies that defy logic. Yes, driving over tree roots will compact the soil, driving the air out. It will eventually kill the trees, usually over a period of three to five years. Placing plywood sheeting over the area helps spread out the compaction, cutting down on the severity of it significantly. That said, I have been building a slide collection over the years that shows trees that should have been dead long ago, as there was no visible source of water, nutrients, or air. Yes, some tree species are more resistant to soil compaction, but don't tell them that or they might die on you!

Q: I have been watering my oak trees with a root watering system about every week to 10 days. But now so many of the leaves are burned around the edges. My county agent thinks the problem is alkaline soil, even though the other plants and trees don't seem to be bothered. He suggested I use MirAcid. Is it possible to apply too much MirAcid? I killed some trees a few years ago by applying too much Miracle-Gro. It says apply one gallon of water with one tablespoon on each 10 square foot area. Could I pour a gallon of the mixture at the base of each tree and not hurt the tree? Or must it be spread out? I sprinkled the mixture on the leaves as per the instruction. If I sprinkled the leaves more than once every two weeks, would it hurt the tree if I am also putting a gallon of the mixture on the ground too?

A: It looks as if your trees are either getting too much water, are planted too deep, or both. I would back off on the fertilizer. It should be used only occasionally and when transplanting.

Q: Last year my parents moved in to a new house which has a large oak tree. It appears to have been two tree trunks growing out of a large main tree trunk. One tree trunk has died and left a gapping hole in the remaining trunk. The hole faces upward, fills with water, and continually gets a variety of ants and bugs in it. They really want to save the tree. It appears healthy everywhere else. The bark seems to be repairing itself and the leaves look very healthy. What would be the best way to prevent any further infestations and repair the hole? (E-mail reference)

A: A certified professional arborist will know what to do. The arborist will clean out the cavity, check the heartwood for soundness and fill in the cavity with a material that will help the bark to grow over it. This is not something that you want to do yourself, I assure you. Besides, the heartwood check is an absolute necessity from what you tell me, as a tree can look very sound and healthy but be rotten in the core, with very little structural strength. The procedure is not expensive, and the knowledge (one way or the other) is worth it!

Q: The house I bought was devoid of trees so I purchased a hybrid live oak three years ago and had the nursery plant it in my backyard. It is now about 13 feet tall and I'm afraid it may be too close to the house at 16 feet away. Another problem is that I also purchased a red oak several months later and it is now 18 feet tall and 20 feet from the house. Are the trees and/or our concrete foundation in danger if we keep the trees? I wish the nursery had given me some kind of warning. (E-mail reference)

A: You have nothing to worry about. If your concrete foundation has no leaks, then the roots are not going to be a problem. If it does, then the roots will only exacerbate the existing problem. These are beautiful trees that have root systems that go way beyond their canopy spread as they mature. Most of the "feeder" roots are within the top 9-12 inches of soil, competing for air, water, and nutrients with annual flowers and vegetables, as well as the turfgrass root system. With intelligent pruning, you will be able to enjoy these beautiful trees for as long as you live.

Q: I have a question about transplanting oak trees. We planted some oak tree seedlings (that our girls brought home from school) at the end of the garden about 10 years ago. One is now about 6 feet tall and the other one is about 8 feet tall. We would like to move them to a different place in the yard. Can this be done when they are this large? When is the best time to move them? And, can we do it manually, or do we have to try and find a tree moving service? (Fargo, N.D.)

A: The older and larger, the more difficult to transplant. Now is not a good time to do it; early spring being the best time. If you have had no experience in moving trees of this size, then you'd be better off hiring it to be done by someone who knows what they are doing. For example, with next spring before leaf-out being the time to move the trees, the tree mover should come in now during this growing season and root-prune the trees. This will greatly lessen the transplant shock that the trees will go through, and give them a better opportunity to survive.

Q: I have a ton of little oak trees sprouting in my grass. They are all caused by the acorns that fell last year that were not raked up. Is there anything I can do to kill off these seedlings without killing my grass? (E-mail reference)

A: Treat them like weeds with an application of a broad-leafed herbicide. It will not hurt the grass and will kill the seedlings. Of course, regular mowing will do the trick as well. I have never known oak seedlings that will survive mowing.

Q: I have a burr oak about 10-12 years old (approx.10 feet high). A few weeks ago I noticed the main trunk bark was a rusty color and appeared to be peeling off. Today I noticed the main trunk has split open; there is a crack longitudinal with the trunk is about 1/8 inch wide several feet long. The tree appears to be getting ready to bud leaves. What is this problem and what can I do to keep it alive and healthy? (Bismarck, N.D.)

A: Sounds like a frost crack has developed and is likely occurring on either the south or west side of the tree where wide swings in tissue temperature can be expected. Unfortunately, there is nothing that can be done, except to hope that callus tissue will seal over the fissure that has developed. To keep this from recurring, wrap the trunk of the tree in sisal-kraft paper, burlap, or simply whitewash the tree trunk this fall, before the cold weather arrives, and remove it before Mother's Day the following spring. While it is unusual for an oak to suffer this kind of winter damage, this can occur to any tree species, especially if any damage was done to the root or branching system some time ago at the time of planting. This could have taken place from pruning or damaged plant parts.

Q: Do you have any tips on how to germinate and then successfully raise oak trees from acorns? I have a couple of acorns that I have stored in the refrigerator from last fall, and I would like to plant them this spring. When should I plant? How large a pot is needed, and given the size of the pot recommendation, how long should I leave the seedlings in them? How much growth can be anticipated in the first year? How should I store the seedlings to ensure that they will live through the next winter? (Fargo, N.D.)

A: When the soil thaws and is free of frost, plant the acorns about 4 inches down, where you want them to grow to maturity. I suggest planting two or three in each hole in case some don't germinate. Of course, if more than one germinates, then simply save the best one by snipping off the others at ground level. Planting them in containers is a good idea, but with the tap roots that develop on oaks, transplanting often causes some losses. You might want to put a protective cone around the planting site to keep the squirrels from getting to them. Since (I assume) you gathered the oaks locally, you need not worry about protection over the winter. They are completely hardy bur oaks that should take off nicely. I would protect them from rodent damage by surrounding them with a plastic or metal collar the first few years. Growth is hard to predict. It depends on the genetic vigor of the acorn. Usually, the first year is just to get established, so growth of about 12-18 inches should be all that can be expected, if that much. Be sure to sow the acorns in a sunny location.

Q: In September 2001 we found an acorn for a bur oak and planted it in a pot here in our office. It is a sapling with seven leaves and 5 inches tall. I looked on the web and through my research discovered that we never should have started growing it in a pot in our office. Or could we consider this a bonsai? Now we are desperate to save it. The leaves are turning brown at the tips. We have kept it moist since planting; never letting it dry out. Is it too much water? Not enough sunlight? (E-mail reference)

A: You did not state where you live, but yes, the acorn should have been planted outdoors rather than as a "houseplant" where it is doomed. I am afraid that there is not much that can be done to save the tree at this point; bur oaks do not make good bonsai specimens, and it is likely getting too much water or is in a poorly drained container. The poor plant is now confused! You have given it a false environment, making it react to what it interprets as "spring" in your office. The leafing out and deciduous nature of the plant is controlled by daylength, so again, the plant doesn't know how to read this human controlled environment and is slowly succumbing. I'd suggest enjoying what days it has left, attempting to adjust the light and watering situation as best you can, and when it finally dies, know that you have learned a good lesson in plant physiology.

Q: I have brown worms that look like meal worms eating the leaves off my small oak trees. They are leaving the vein part but stripping the leaves clean. There are literally hundreds of them and my extension agent is on vacation. Can you please help before my trees are killed. (E-mail reference)

A: Not to worry, the trees will survive. Spray with either Malathion or Sevin ASAP to get a kill-down. Then spray with a dormant oil spray next spring before the trees leaf out to kill any overwintering insect eggs.

Q: I have a beautiful white oak in my back yard that appears to be suffering. The bark is splitting near the base, and I have numerous white growths with reddish stripes on the backs of the leaves near the base. They appear to be insects. I've not seen this anywhere before. Any suggestions? (Bemidji, Minn.)

A: What you are describing sounds fairly normal. The tree will have bark exfoliate at the base as it grows and matures; the leaves are frequently attacked early in the spring by mites or small insects that lay eggs in the unfolding leaf tissue that causes gall growth, which is often noticed at this time of year. These are typically nothing to worry about, and they go in cycles, without harming the tree. No action is warranted, and would be useless at this time anyway.

Q: Any advice on why the acorns on our oak are falling in early July? The nuts are premature, barely formed inside the caps, but they're dropping by the dozen each day. (E-mail reference)

A: If you open up one of those acorns, you will probably find a small white grub, or evidence of past presence via the exit holes, that are or have been feeding on the acorn meat. If the nuts appear sound and are not hollowed out by this borer, then it could be just superfluous nut drop from too heavy a crop. In either case, there is nothing you can do about the situation at this time.

Q: I am a long way from your location (southeast Texas), but I hope you can give me some advice about a problem I am having with my red oak trees. Recently I have noticed patches of the bark change color, usually in areas of about 10 inches by 10 inches. I can pull the bark off by hand and underneath I find what I think is hard wood. I don't think that the bark is growing back where it has come off, because the color is more like weathered wood and does not have the thickness of the original bark. I have been in this house for over 20 years and I have never seen the trees do this. Should I fertilize the trees? If so, what should I fertilize them with? Should I spray them with a fungicide? The trees are about 60 years old and have well established branches. (E-mail reference, Texas)
A: I'm willing to bet that the oak you are making reference to in your part of the country is the live oak -- Quercus virginiana. It is characteristic of this tree to develop a platy, alligator-type bark with age that fits your description. Some exfoliation is common with fluctuations of moisture and temperature. Generally the leaf color and density is a good indicator of any fertilizer need. If the internode growth (the area between the buds or leaves) is shrinking, or the foliage is appearing chlorotic, then some fertilization may be called for. If there are no symptoms of disease or insect problems, I'd suggest not spraying, as to do so without overwhelming evidence would only throw nature out of balance and open the door for parasites to move in.

Q: While at the Minnesota Zoo last summer I picked up what appears to be an acorn from the trees growing at the zoo. I would like to plant it here in South Dakota. Do I crack the shell and plant only the seed inside? How deep? Does it require a lot of water? Will it grow in South Dakota? (E-mail reference, S.D.)

A: There are some two or three dozen oak species that could be growing in the Minnesota Zoo. If the oak seed is still viable, I suggest getting some unmilled sphagnum moss, soaking it completely, then wringing it out and wrapping it around the seed (acorn). Place that in the vegetable crisper in your refrigerator, and when spring finally arrives in April, check it to see if a root has begun to emerge. If so, plant it carefully, about 3 inches deep where you want the tree to be when it matures -- so give it a lot of space! If nothing has emerged by this spring, then throw it away, as it likely not a viable (living) seed.

Q: I have a bur oak that I picked up in Bemidji, Minn., about 12 years ago. This fall after the leaves fell, I noticed grape sized brown clusters (with an exit hole in each?) on a few of the branches. I am wondering if this is a concern and how to treat? (Jamestown, N.D., e-mail)

A: Thanks for the good description. Not a concern. This is one of the many galls that affect oak trees. They come and go, and are caused by mites or small wasps. Control is not necessary, and attempts are usually ineffective anyway. If their presence bothers you, I suggest pruning the clusters off early next spring before new growth begins.

Q: I have a cluster of four red oaks and a twin oak in my yard that are losing their leaves very fast. (Detroit Lakes, Minn.)

A: You have a couple of things going on. Most likely is a change in the water table. If it is coming up, that could cause the defoliation you are witnessing. And second, the leaf spots are a fungus known as Marssonina martini. Severe infections can also cause defoliation.

The best control is to practice good sanitation this fall by cleaning up all fallen leaves. It would be a good idea to spray the trees next spring before the leaves come out with lime-sulfur, as this is an excellent sanitizer.

Q: The fern peonies here in town have now begun to brown and fall down. Can they be cut to the ground yet? I know the leaves of dandelions that currently are growing freeze over the winter, but do new shoots come from the existing plant next spring? In other words, is it of value to spray and kill the current plants to ward off them reappearing again in the spring? I have red twig dogwoods that have exploded out of control this summer. Beautiful, but drooping with new growth making for difficulty mowing under them. How does one deal with such ambitious growth? It seems to me that certain oaks at the farm produce way more acorns than other oaks of the same size. I think that there are some oaks that produce no acorns, but I could be wrong about that. Any thoughts on this? (Fertile, Minn., e-mail)

A: Cut down your peonies. Spray your dandelions. As for dealing with your dogwoods, the best method is to cut them back to make mowing easier. Not to worry, they are completely winter hardy and will not suffer from a late summer pruning. The other way, tying them up, is a band-aid approach and not very effective or pretty.

And, it is true that some oak trees are more fruitful than others. Sometimes the fruiting is related to the stress the trees are under, as well as the age. Older, stressed trees will tend to fruit heavier, while younger (but still mature enough) less stressed trees will go fruitless or bear very little fruit. Another reason could be hardiness. The flower bud is less hardy than the leaf bud. Hence, the oak that is marginal in hardiness may get caught in a late spring freeze that kills the flower bud, but doesn't harm the leaf bud.

Q: My oak tree is showing symptoms of stress with the leaves browning and dying at the ends of the branches that have worm tunnels. There are several trees in the community showing this stress condition. (Fergus Falls, Minn.)

A: Judging by the size of the boring hole, the culprit appears to be the carpenterworm. The grub stage is the destructive phase in the life cycle. The adult is a moth. If possible, cut back the branches infested with the borer and burn. This will require the services of a professional arborist because of the size of the trees. Next, spray the trees with methoxychlor or chlorpyrifos in spring and summer. Do all you can to maintain tree health and vigor--fertilize, water, prune etc. Once begun, borers are not easily controlled!

Q: All the oaks in Lisbon seem to have the same problem that my 5-year-old oak is having. Please let me know how to fix it. (Lisbon, N.D., e-mail)

A: You have nothing to worry about concerning the galls you see on the bur oak foliage. These galls are caused by a nonstinging miniature wasp laying eggs in the unfolding foliage in the early spring. The actual galls are believed to be caused by plant growth regulating chemicals that are produced by the insect. These and other galls are so commonly associated with oaks that people regard them as typical structures of the plant--that is, considered "normal."

Yours is called the "jumping oak gall," caused by Neuroterus saltatorius. After the larvae hatch they move so violently they actually cause the gall to move or jump. At the stage you are now noticing them, the insect inside the gall has already departed. So what you are seeing is the "former home" of the young.

No action is suggested or warranted. Just your normal care of the tree is all that is needed. Keep in mind that these characters evolved together eons before mankind ever realized their existence!

Q: There are "balls" growing on my oak tree. What are they? (Galesburg, N.D.)

A: Your sample was of the oak bullet gall wasp—Disholocaspis quercusmammor. Their damage is cosmetic, not lethal. No control is necessary or practical.

Q: Can you tell me why the leaves on my global arborvitae are turning brown? I also have been trying to start a bur oak from acorns, but I haven't had any luck. Can you explain why? (Gettysburg, S.D.)

A: The global arborvitae is suffering from winter desiccation. Protect it in the fall by spraying it with Wilt-Pruf. This keeps the foliage from drying out. Respray again with the first late winter thaw to keep the spring winds from drying the foliage. 

Bur oak need about 40 days of stratification with day temperature at 86 F and nights at 68 F. Under these conditions, the germination rate ranges from 28 to 85 percent, for an average of 45 percent. For every 10 seeds or acorns set out, on average, four to five would germinate. This requires lots of patience!

Q: Following is a technique for the person who was asking about transplanting bur oaks.

One of the easiest ways is to collect the acorns or nuts right after they have dropped to the ground and sow them a few inches deep at points where you want that kind of tree. Drive a stick or marker at each point to aid in finding the seedlings the following spring. Acorns with small worm holes probably won't germinate.

The Soil Conservation districts have been successfully planting bur oak seedlings in shelterbelts. I have several started that way. As I understand the technique, the young seedlings are root-pruned in the nursery row and may be replanted one or more times.

In 1960 I planted nursery-grown bur oaks. Years later a man hired a firm with a tree moving machine to move several kinds of my trees to his business place. One of these was a bur oak. There was complete success. Later four new bur oak whips came up from the removed oak and have developed into a very attractive group.

A: Thanks for the information on transplanting and seedling establishment. It will make interesting reading and good information to our readers.

Q: What is the secret for transplanting bur oak? I have tried three in the last two years without success. (Rugby, N.D.)

A: The secret is that bur oaks don't transplant! Their taproot system is literally destroyed when they are dug up. Try gathering acorns and planting them where you want them. They need no fertilizer.

Q: Can you tell me if the plant in the picture is an azalea? In your column you are always saying that they are hard to grow, but mine is doing beautifully! Can you also give me some information on growing oak trees from acorns? A few years ago I threw some out and now I have a beautiful tree, but I haven't had any luck since. (Wilton, N.D.)

A: Of coursetry to grow something and it won'ttreat it with indifference and it will! Actually you are likely running into one or both of the following problems: the acorns are either immature or an acorn borer has hollowed out the "meat" inside. Basically, you are doing the right thingplanting the seeds in the fall, and looking for something to emerge next spring. Keep a wary eye out for squirrels too!

Yes, that is an azaleathe Indica type. Whatever you are doing keep it up! You've got a beauty!

Q. Help! What is happening to our majestic oak trees? Here are samples from two trees in the yard in different locations. Some branches are bare and very dead. Can you detect the  problem and provide a solution?

I've gleaned a lot of helpful info from your column. Others write in about their problem (and sometimes mine) and there's the answer. I like that. Keep on enlightening all of us!  Thank you.

I should mention all the evergreens are dying from Rhizosphaera needle cast. Any connection? (Fosston, Minn.)

A. Thank you for the very kind words!

I'm sorry, but I have bad news. Your majestic oaks are infected with a fungus known as Oak wilt, a degenerative, vascular pathogen, that essentially shuts down the functional   vessels of the sapwood. The only course of action open to you is to turn them into firewood.

The Rhizosphaera needle cast on your evergreens is not connection to the problem with your oaks.

Q. I look forward to your column every week. Thanks for the great information!

I am wanting to plant a couple of trees in our front yard (south side), such as a spruce or pine. However, I don't want them to get more than 7 to 8 feet tall. I also want ones that will not winter burn (I've had bad luck with this as my two dwarf Alberta spruces are beyond saving).Can you recommend a good, hardy, not-too-tall tree that will survive our tough winters?

Also, we planted an oak tree from a sapling about eight years ago. It is now about 10 feet tall, but there are actually three trees coming up from the ground. We are now realizing that we should have removed the other two long ago, and are wondering can we still do this? Will the largest one branch out to fill in where the others were?

Your help is much appreciated. (Moorhead, Minn.)

A. Thank you for the compliment about the column.

Sorry, but there are no guarantees on our evergreens surviving without winter burn in our part of the country. Even the toughest will be subject to some injury--sometime.

The best suggestion I can come up with is a Siberian Arborvitae, Thuja occidentalis `Wareana.' This will get about 10 to 18 feet tall, as close as I can come to your height request. It is commonly used in shelterbelt plantings, so it has to be tough.

Why not leave your "oak tree cluster" as is and have something different? There are "clump birches," why not "clump oaks"? Could be you would start a new trend. Honestly though, you are likely to cause more problems at this stage with an attempted removal of the other two trees--to the point of possibly losing the one you want.

Stay with what you have and work on creating an attractive landscape specimen.

Thanks for writing.

Q: We have an oak tree in our yard that is about 20 feet tall. We have raised it from an acorn and have had no concerns about it until recently. During the spring, we started to notice that the bark was gone on the main trunk, right under where branches go out of it. Just recently I have noticed that a great deal of bark has apparently been removed due to pecking. We have never seen any birds doing it, but suspect that is what is happening. We do have woodpeckers at our suet feeder daily, so they are certainly around. It is there anything we can do to protect the tree? With so much bark missing, I am concerned about its survival. (e-mail)

A: Woodpeckers and sapsuckers can be visually destructive to some trees when they are actively setting up territories or attempting to attract mates. It is the males who are "showing off" to attract a female. Typical, right? First of all, these birds are protected under federal and state law, so they cannot be legally shot. Next, a little annoyance or scare tactic will usually discourage most. Hanging aluminum pie tins or aluminum strips around where they are actively drumming will discourage them. Also, a material used to trap the female cankerworm--Tanglefoot--will make the area so sticky that they unlikely to come back. A final method is to discourage the drumming sound by wrapping some insulation around the area they frequent. Being songless birds, they need to find a surface on which to make their drumming sound, and with soft insulation covering the surface, their efforts will be thwarted.

Q: For some time now I have been trying to grow oak trees from the seeds they drop. Is there some secret that I don't know? (Pollock, S.D.)

A: Acorns can be mined by weevils quite frequently. Generally, this mining is determined by a "float test," whereby the mined ones will float to the top in a pail of water while the sound ones will sink. Also, acorns need an overwintering or cooling treatment. What often happens is the acorns are collected, checked out for soundness and then planted. Squirrels or other nut-eating critters in the area find them. I've seen it happen many times. There are two basic categories of oaks: the white oak group with rounded leaf edges and the red oak group with the pointed leaves. The white oak group will germinate readily if they are sound, once they have dropped to the ground; the red oak group needs cold stratification for 90 days, generally, at a temperature of between 32 F and 41 F. If you are successful in collecting some sound acorns from the ground next fall, sow them in rows about 1 foot apart and cover with about 1 inch of firmed soil. Mulch the planting with leaves and hold them in place with hardware cloth, which also will keep the rodents at bay. After spring frosts are past, remove the mulch and the hardware cloth.

Q: I've read that there are new oak hybrids: Dakota Sunrise Bur Oak, and Mongolian Oak. Where can I buy such trees? I don't have the slightest idea who would sell them? Also, is there a book about the bur oak? I know these would be unlikely, but I have many in my area, and they are my favorite tree. (Hawley, Minn., e-mail)

A: When new hybrids like this are first released, they are often difficult to locate, but keep asking at locally owned garden centers, as they are most likely to be getting such stock shipped in. Perhaps someone can special order it for you. I know of no book dedicated specifically to the bur oak.

Q: We have a serious defoliation of oak trees this spring due to an oak tree worm that pupates in the leaves then rains down on webs to later become moths. Do you know about this phenomenon? (Southern California e-mail)

A: It sounds like you have a gypsy moth problem. These pests were imported into the United States from Europe in 1869 for possible use in silk production. Some escaped and have become entrenched as pests across the entire continent. Unfortunately, oaks are one of the favorites of these defoliators. Sex traps (pheromones) will take care of future generations, and a biological, Bacillus thuringensis (Bt) sprayed before the fourth instar larvae appear will be effective in controlling the present generation without harming any other biological life in the area. Foliar sprays are largely ineffective because of their ability to penetrate the tree canopy. If this is the first defoliation of the tree, don't worry, it will releaf again. But keep a vigil for these pests because repeated defoliations will kill the tree.

Q: We have a group of four red oaks ranging from 6 to 9 inches in diameter. Two have only about 10 percent of their leaves and the other two about 30 percent. The trees are in a low area and are not starved for moisture. We have many maple trees and a twin red oak up on higher ground that show no signs of trouble. Also, I have not noticed any sign of worms. What might be the problem? (Detroit Lakes, Minn.)

A: Most likely a change in the water table. Oaks do not like continuously moist root zone conditions, and will respond exactly the way you describe when that situation occurs. You need to find some way to lower the water table to get them to survive.

Q: The leaves on my pin oaks are curling up but not turning brown. I can see raised tunnels in the center of every leaf. What’s wrong? (e-mail reference)

A: A member of the red oak group, the pin oak is subject to gall damage, which in most cases is just cosmetic. It sounds like yours is the vein pocket gall. Generally, there is nothing one can do to control these galls. Unless other problems start to manifest themselves--premature leaf drop, discoloration or attack by other foliage destroying insects--you can sit back and enjoy one of the small wonders of mother nature. In the fall, rake up and destroy all the fallen leaf litter to help break the cycle of reinfestation.

Q: We are going to build a home at our lake place, which has a very old oak tree about 30 feet tall. Since our building space is very limited, we would like to get as close to this oak tree as possible and still not hurt the tree. How far away do we need to be when digging a foundation? The contractors estimate they may have to dig about 12 to 16 inches for the foundation. The oak’s drip line is about 17 feet. Do we need to stay out that far? (Minnesota e-mail)

A: The farther the better. I would say the drip line should be the minimum. Be sure that the contractors make clean cuts on the roots they need to remove. Many just rip them with either a backhoe or trencher, which opens the door to many problems. Equally important, avoid compaction around the root system as much as possible. To do this, have the contractors lay down 4x8 sheets of plywood or steel plating where they are going to be driving heavy equipment over the roots. If it is maltreated, the oak tree will not die right away but will gradually decline over several years, eventually dying three to five years after the construction is completed.

Q: I have a bur oak that is about 5 feet tall. All summer it has been covered with large ants. Will they hurt it and how can I get them off? (Tappen, N.D.)

A: The ants are "working the aphids," which are more difficult to detect. The aphids feed on the foliage and stem tissue, secreting a "honeydew" which the ants harvest for food. Nothing to worry about!

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