March 30, 2006

Hortiscope

Ronald C. Smith, Horticulturist
NDSU Extension Service

Q: I bought a house with at least 10 hydrangea plants. Approximately 70 percent bloomed last summer. I think some are old-growth and some are new-growth blooms. How do I know for sure what is old or new growth? I'd like to prune the new-growth varieties, but don't want to risk losing the old-growth blooms. (e-mail reference)

A: When in doubt, strike a compromise. Prune half the branches and see what comes, flowers on the new growth or the old. Take notes and prune accordingly each year.

Q: I have a clover plant I love. I am having problems with aphids and white bugs. What can I do to get rid of this problem? Would using a soap-and-water spray work? I have tried using Schultz bug spray, but it seems to kill the plant. (e-mail reference)

A: Try an insecticidal soap. It has the right formulation to kill bugs on houseplants, but will not damage the plant.

Q: I have a large caliper crabapple tree that I planted last summer. Rabbits have removed the bark from approximately two-thirds of the height of the trunk. What are the chances the tree will survive? What can I do to save the tree? Should I graft or paint? (e-mail reference)

A: Start a national campaign on the health benefits of eating rabbit meat! From your description, the tree is a goner. You can attempt what is known as bridge grafting, but from the damage you describe, I sincerely think it would be a waste of time and effort. Rabbits can be controlled a number of ways. Wrap the trunk as high as possible and spray the remaining bare branches with Hinder, Liquid Fence or a hot pepper spray.

Q: This weekend our boys had over some friends who have a snowmobile. The boys ran over one of my lilac bushes. It snapped off at the base of the plant. Can the bush be rerooted? The roots are still in the ground. Will a new bush start to grow? Any information you can give me would be great. (e-mail reference)

A: Most likely, no serious harm was done, so you can let them out of the dungeon. Plants probably will sprout from the roots, but will not flower this year. The plants should flower next year, assuming the boys don't do the same thing again!

Q: I live on a farm with a large flower bed that is not well protected from the wind and gets a lot of direct sunlight. I would like to know your opinion about mulch. What is the best mulch to use that is readily available, doesn't have a lot of side effects and is relatively inexpensive? I have access to wood chips, but am concerned about the pros and cons of using wood chips. I also would like information on ornamental evergreens and conifers. I have seen several in seed catalogs that are weeping and some that are more blue or golden, but I do not always trust the information given in these catalogs. Also, I like the unusual look of the walking stick and the curly willow in the winter, but understand that both are not that great to look at in the summer. Is there anything that looks great throughout the year? I look forward to your column every week and appreciate any advice I can get from you. (Jamestown, N.D.)

A: Thanks for being a faithful reader of the column! You can use wood chip mulch without adverse side effects if the mulch has had a chance to cure or compost for at least one season. The exception might be black walnut chips if you are going to grow tomatoes or other members of this family. Just don't exceed 3 inches in depth. The evergreens that are common in our area are the Colorado blue spruce. I would encourage you to steer clear of that species and look into something else, such as Black Hills spruce, ponderosa or Swiss stone pine. For anything to look great throughout the year is a tall order. How many humans do you know who can make that claim? However, the river birch looks great throughout the year, as does the copper curls pekin lilac. The exfoliating bark on both plants is an attraction throughout the year.

Q: When choosing between Colorado or Black Hills spruce, what do you suggest? When selecting height of the conifer, is there a maximum that you would recommend for transplanting? We would like to go as large as possible without significantly decreasing our success rate. (e-mail reference)

A: I favor Black Hills spruce because of its softer needles, uniqueness in landscapes for the area and its uncharacteristic growth into maturity. Balled-in-burlap plants about 5 to 6 feet tall have, in my experience, turned out to be the easiest to establish. Coming from a nursery, the plants should have been root-pruned (check this out to be sure) every year before being harvested. That way, most of the roots the trees developed would be present at transplanting.

Q: I bought a Christmas cactus plant that I water when it is dry on top. Lately I have noticed little, black, gnat-looking bugs on the plant. What is a safe way to get rid of them without killing my cactus? (e-mail reference)

A: I would suggest repotting with fresh potting soil that is pasteurized. These are likely fungus gnats that are feeding on the organic matter in the soil mix, which was probably not a pasteurized mix to begin with.

Q: I have an apple tree (honey crisp) that is seven to eight years old. The first year it produced fruit was two years ago. Last summer it did not flower, but I was told that apple trees only produce every other year. Is this correct? I am wondering if I should plant another apple tree in the yard. If so, what kind? Last year I had a severe infestation of grub worms. In fact, the worms destroyed about 25 percent of my yard. Last fall I had the bare spots rototilled to a depth of about 4 inches and then planted grass seed. Should I apply some type of chemical on these spots or was this infestation a one-time thing? None of my neighbors had worm problems. Why me? Also, I have a green ash tree. For the past few years, it has developed what look like clusters of grapes on the branches. I thought when it froze they would die and fall off. Instead, the grapelike clusters stay on the tree and turn black. The problem does not seem to have hurt the tree. What should I do? (e-mail reference)

A: You can plant any apple or crabapple tree you want. The cross-pollination will work. Alternate bearing is something that usually takes place if there is a particularly heavy fruit set one year, which is followed by a lighter one the following season. Have a lawn company come in this spring and apply a soil insecticide. There are many types of lawn grubs, depending on what the adult beetle species was, that could lead to a year or two cycle of grub feeding. The grubs then emerge as adults, feed on the surrounding foliage and lay eggs in the soil. Your problem with the ash tree is ash flower gall. It is caused by the feeding of a mite on the flower clusters. The damage is cosmetic and will not hurt the tree. Sprays can control the mites, but the timing is extremely critical. Spraying is not worth the frustration of trying to get the timing right along with the expense and environmental impact. If you can reach the clusters with a pole pruner without climbing a ladder, you might be able to cut them out.

Q: We have hundreds of beautiful irises, but we are moving. In a panic the last warm winter day (March 3), I dug up a bunch of them. Is it OK to store the plants in crates until I am ready to replant in late summer? My concern is that there are some green stalks and leaves. Could I temporarily store them in some sort of soil mixture? (e-mail reference)

A: Pot the irises for the time being. Once they get started, it is hard to stop the forces of nature.

Q: I received a cyclamen plant last October that had beautiful flowers. I noticed the pot was getting too small, so I repotted the plant. It has not flowered since then. The plant grows many leaves that are hearty and strong, but no flowers. The plant receives plenty of sunlight during the day and is cool at night (65 degrees). I have been watering it once a week. (e-mail reference)

A: My best advice is to be patient. The plant will get around to flowering because you appear to have it in the right growing conditions and giving it the care it needs.

Q: I have an old willow tree in my yard. This year there were many dead limbs and the bark was peeling off. We pulled off the bark and found many little bugs that we call pill or roly-poly bugs. When you touch the bugs, they curl up in a little ball. The bugs look like they have sectional bodies. What can I do to keep these bugs away? (e-mail reference)

A: Get rid of the rotting willow! The bugs are detritus feeders that eat decaying organic matter. The willow apparently has an abundance of decaying matter. If the tree is important to you, have an International Society of Arboriculture certified arborist inspect the tree to determine if the tree can be saved and look for other possible insect and disease problems.

Q: Bishop’s weed is taking over the edges of my garden. I've heard the weed is unstoppable and undeterred by Roundup. Any suggestions? (e-mail reference)

A: Let this be a lesson to all who read this column. Bishop's weed, Aegepodium podgaria, also known as goutweed, is an invasive, herbaceous perennial that creeps through rhizomes. Through aggressive competition, the weed eliminates other species of plants. The best control is probably glyphosate (Roundup), which should be applied with a sticker-spreader material to make sure it translocates through the plant. You also can try any dicamba-based herbicides, such as Trimec, which is selective to broadleaf plants. It will be a long and tedious battle no matter what methods of control or elimination you try. Don't purchase the RTU version of Roundup. Get the straight chemical and make your own mixture following label directions. It will be more potent.

Q: My students are trying to research chokecherries. We are trying to find out if they are native to North Dakota. How far back can chokecherries be traced in North Dakota history? Could you provide some information or direct me to where I could have the students do some research? (e-mail reference)

A: Chokecherries, Prunus virginiana, are native to most of the eastern U.S. and Canada and extend west into the northern Great Plains, which includes North Dakota. Chokecherries were a source of food for the colonists. American Indians introduced the settlers to the tart fruit. A thesis probably could be written about this small tree, so I would suggest the students do a Google search on the plant and see what pops up!

Q: While mowing the grass this past summer at the New Rockford golf course, a hydraulic line burst. It left a trail of hot hydraulic oil on the grass and killed it. Can I plant new seed or do I have to dig out the contaminated dirt, backfill and then reseed? How far down should I dig? (e-mail reference)

A: You have to dig out the contaminated soil. Sorry! I would dig down at least as far as there is evidence of oil penetration and then some. There is no point in leaving any residue because it will kill your grass later on as the roots penetrate the soil.

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Source: Ron Smith, (701) 231-8161, ronsmith@ndsuext.nodak.edu
Editor: Rich Mattern, (701) 231-6136, richard.mattern@ndsu.nodak.edu

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