June 19, 2003

Hortiscope

Ronald C. Smith, Horticulturist
NDSU Extension Service

Q: In the spring of 2000 we planted Siouxland cottonwoods which did very well but last spring (2002) we had 18 trees die. The rest did well last summer but this spring we had more die. The trees are at least 8 feet tall and are dying from about the one-foot level and up. We have been tilling the tree rows so there is no grass or insulation near the trees. Could they be dying because there is a lack of snow cover? Should I cut the dead branches off and see what happens? The main trunk seems dead except for branches near the bottom. The roots must be somewhat healthy to be keeping a few branches alive. (E-mail reference)

A: Go ahead and cut off the dead material and go lightly on the tilling. Too much too close will damage the roots and set the plant back. Siouxland is a poplar that has a whole encyclopedia of diseases that can debilitate it. Usually it doesn’t occur this early in a planting. Diseases mostly happen when they are just starting to be of value to the owner. Your dieback could be due to any number of problems, including the weather.

Q: I bought 20 Colorado blue spruce to plant at my new home on land which adjoins my current home. But after reading your column I'm thinking maybe I should have purchased Black Hills spruce instead. You don't explain in the article why you don't recommend blue spruce. Is there a high mortality for blue spruce? What can I do to help them survive? They're probably already shipped so I don't think I can change my order. What advice can you give me for growing healthy, fast-growing blue spruce? (Moorhead, Minn.)

A: It is partially a bias on my part and the fact that they have been grossly over-planted. Go ahead and plant them when they arrive and give them normal TLC and I am sure they will do very well. As a member of a landscape crew when I was a lot younger, I grew to hate those plants because of their hypodermic needles that pierced even long sleeved shirts. We were of course planting 6 foot tall specimens at the time not the small seedlings you will be getting.

Q: We have a 27-year-old Marc Michel lilac. It still blooms but only on top. Some of the main branches are dead and on many others the bark is split and drying and even dropping from the branches. Normally this variety blooms the standard mauve color but part of this tree blooms very light, almost white. There are very few leaves on many of the branches. Should we prune it severely? (E-mail reference)

A: Cut the old, dead branches out completely back to the ground. This should cause a surge of new growth which you can then fashion to your desire next year. Do this every year and you should have a perpetually young plant. If there is no response to this treatment, then it is time to replace the shrub.

Q: I have two spider plants which I neglected a little over the winter and now I'm trying to get them to come back to life. A lot of the leaves are bent. Would it be okay if I trimmed the leaves past their bent spots? (E-mail reference)

A: Be my guest is that it won't hurt them a bit. You might consider summering them outdoors to help revive them.

Q: I have an apple tree that is about 10 years old. I just got a dog and he is chained to the tree at times. To my surprise he has stripped most of the bark from around the trunk. I have wrapped it in plastic and stapled a wire mesh to it. Please let me know if it's too late or if I can do something to help it. (E-mail reference)

A: It is probably too late from what you’ve told me but you can never tell. If it is still holding leaves, you may be in luck, especially if it leafs out next spring. There’s not much more you can do except keep the dog away from it.

Q: I have three apricot trees about eight years old which started to bear fruit the last few years. Last year they bore fruit which grew to maturity but the apricots were covered with brownish black spots. What is it? Can I spray with anything to save the crop? Otherwise, the trees look healthy. Also, what can I spray for cedar apple rust? We have a couple of cedars with apples but it’s only the second time in 15 years. (Barnesville, Minn.)

A: The spots on the apricots are likely a fungal leaf spot. Clean up all the fallen leaves then next spring spray using a Bordeaux mixture to prevent the spores from developing. The best bet to control cedar apple rust is to remove one of the alternate hosts to control the rust cycles. The next best bet is to pick off the fruiting bodies on the junipers or the witch's broom. Lastly, spray them with a fungicide just as the gelatinous bodies are developing on the junipers.

Q: Last year I bought two maples which were supposed to be Norway maples however one came out green while the other is red. Can you tell me what the red one is? It was green last year. (E-mail reference)

A: It could be that the new growth is simply manifesting the red coloration which will change as the foliage matures. Or, you may have been given one of the red leaf cultivars such as Schwedler's or crimson king. If you did, lucky you!

Q: I just bought a house with a huge lilac bush right by the house. I would like to get it away from the house but it has a huge trunk. Can I get little lilac bushes even if there aren’t any growing from the ground, just a big trunk? Can you grow roots from branches? (E-mail reference)

A: Yes you can. It’s called asexual propagation via cuttings. You can also be assured that if you were to cut this shrub down, you would get a plethora of sprouts coming up from the root system. That may be the easiest thing to do. You can then dig up the desired sprouts next spring before they leaf out and plant them where you wish.

Q: You have often mentioned pruning lilacs back to ground or soil level. What does that mean? I have two lilac bushes in my back yard which seem to bloom much later than everyone else’s. They bloom but not for very long. Everyone says we should prune them back but I don’t have a green thumb. I haven’t the foggiest what pruning back means. I have always enjoyed the smell of lilacs and would love for these bushes to thrive. (E-mail reference)

A: Lilacs should be pruned back to ground level only if you want to rejuvenate the plant. Normally, to keep them to a manageable size, keep them pruned on a regular basis to suit your taste. Do it right after the flowers have faded but before July 1. I would suggest purchasing a couple of good books on gardening and horticulture from a local bookstore.

Q: I have a few thousand trees that I planted over the years. I plant a thousand or so each spring for deer habitat or cover on a couple of pieces of property that I have. I also have a number of trees in my yard as well. I get my fertilizer in bulk from the local grain terminal. A friend has used a handful of 30-10-10 for years which he seems to have good luck with so I use it too. I use a one ounce jar full per tree. I place it at the base of the trees which are covered by fabric. I’m not sure if this is hurting anything or not. I do it in the spring and sometimes in the fall. I also toss a couple of cups or more around the large spruce trees in my yard and one cup on my "B&B" trees. I have lost some trees in my yard but I believe fertilizer is not the problem. I have lost some to tree protectors, damage by a weed eater and because I have tried to grow zone 5 trees in zone 4. I won't try that again! Also I have a number of maples that have had plastic protectors on for a couple of years. I took them off this spring to find that some had lost a few feet of bark on one side. Did I leave them on too long?

A: Fertilizer placed at the base of a tree does little good. Your fertilization efforts, in all likelihood, are not benefitting the trees and, most certainly, they do not need the fertilization regime you are following. Tree roots are uncanny miners of nutrients from the soil. Fertilization is recommended, in most cases, only when deficiencies are suspected and can be confirmed with a soil or leaf tissue test. If fertilization is then called for, it is calculated by the spread of the tree. A precise amount is either spread under the canopy or injected into the soil at root depth near the feeder roots but not near the trunk where the roots are functioning as a prop for the trees. The fertilizer you are using is more suited for turfgrass than for trees. A lower level of nitrogen is recommended (10-10-10) so that leaching beyond the root zone doesn't take place or the tree isn't overstimulated into excessive foliar growth.

Q: I have a lot of spiderettes so I’m wondering if they could be put outside in hanging pots for the summer. Would direct sunlight be too much? (E-mail reference)

A: I would encourage you to put them outside under an overhang or in the canopy of a yard tree. Direct sunlight, depending on where you live, for six or more hours might be a little too much - at least all at once.

Q: Can you tell me how to determine if some rhubarb growing on the edge of my lawn is safe to eat? (E-mail reference)

A: If it looks normal in every way, where it is growing should not make any difference.

Q: I have a weeping birch that is about 17 years old and 50 to 60 feet tall. It’s a very nice tree and we enjoy it very much. This spring it leafed out very nicely but about a week ago I noticed that, about 10 feet from the top, the leaves had turned brown and were dying. What happened? I hope it doesn't continue down the tree. Anything I can or should do? (Carrington N.D.)

A: The same thing that is happening to my 18-year-old weeping birch. You have bronze birch borer damage. About the only thing you can do is hire an arborist to come out and trim it back to fresh wood. If licensed, have the arborist inject some insecticide into the trunk and hope that you got to it in time. I hope I can milk a few more years out of mine. The one arborist in Fargo that was servicing the tree is now out of business or moved. I hate the thought of losing this beautiful tree but it was worth enjoying it over the years that it thrived.

Q: I have a Lonicera x Brownii 'Dropmore Scarlet Trumpet'. It is 2-years-old and more than 5 feet tall with several blooms. Recently I noticed that something has eaten nearly all the blooms leaving the tips slightly black. Quite a few of the leaves have holes and some are stripped of all but the leading vein down the leaf. I have looked carefully at the leaves but can’t find any bugs or eggs. It leads me to think the problem isn’t aphids but I’m at a loss as to how to protect my plant. I would prefer using a natural method to control the problem since I don’t use chemicals. (Moorhead, Minn.)

A: I suspect slugs are your problem. Tonight, to see if you can catch some, set out empty tuna cans full of beer with the edge just above ground level. Any saucer will do if you don't have a supply of empty tuna cans laying around. You can't get more natural than beer!

Q: I would like to know if the hackberry tree, its bark or leaves are poisonous to horses? (E-mail reference)

A: It’s not according to my references.

Do you have a gardening or houseplant question? Write to Hortiscope, Box 5051, NDSU Extension Service, Fargo, ND 58105 or e-mail to Ron Smith at ronsmith@ndsuext.nodak.edu. Note to e-mail correspondents: please identify your location (city and state) for most accurate recommendations.

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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