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Ron Smith answers questions about flowers, trees, gardens and shrubs.

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I have two rows of arborvitaes that vary in height. Some are leaning and some bent almost at a 90-degree angle. Some of the stems are bent about halfway down. Unfortunately, there isn't room to stake them up because of a parking lot a few feet from the trees. Any ideas how we could save these trees? Would it help to trim them or take some of the bent tops off? Could we tie some together? (e-mail reference)

A: Yes to all of your questions. Tying them up should be a temporary treatment until new growth begins this spring. However, don't use twine or rope to do it as it may cut and girdle the stems. Check the stems to be sure there are no breaks where they are bent. This often happens and the tree usually does a poor job of healing if that is the case. If you are unsure of what exactly to do, I encourage you to contact a competent tree care service to do the job. Look for an International Society of Arboriculture certified arborist when considering what tree company to hire.

Q: I would like to build my own greenhouse or purchase one. If I purchase a greenhouse, would 4 mil be thick enough for the walls or would double walls be better? If I built one, I was wondering if the panels that you see on top of buildings that are white and let light in would work for the walls and ceiling. I am not sure if the panels would let in enough light and heat to grow plants. Also, do you know where to find the seeds on a geranium plant? (e-mail reference)

A: In greenhouse construction in this part of the country, double walls would be best. The white panels are acceptable for the noncommercial growing of plants. Clear would allow in more light, which we sometimes desperately need during the year. It all depends on what it is you intend to grow. Geranium seeds can be found at the base of the spent geranium flower.

Q: We just bought a flowering Robinson crab tree. What is a good fertilizer for it? Do we fertilize at first planting? Do we use an acid fertilizer? (Zimmerman, Minn.)

A: No fertilizer! Plant the tree at the right depth, water in well and stand back to let nature take its course. If your soil supports weed growth, it will support the growth of this tree without any outside input other than water to get it off to a good start.

Q: We have mature lilac bushes that were damaged by cattle this winter. We are snowbirds and returned to find our neighbor’s cattle had gotten into our yard and eaten the small branches and broken most of the larger branches. They also rubbed their horns on the stems and removed the bark from a lot of them. They look pretty sick right now. I am seeking advice about how to salvage the bushes. The tops of the bushes are undamaged. (Thompson, N.D.)

A: The best thing you can do is to cut the damaged branches back to as low as possible. This will encourage new growth from the crown of the plants. If you allow the damaged branches to remain, they may or may not recover. This would leave the damaged branches vulnerable to cankers and other diseases that could become a bigger problem. If there are healthy branches left where the damage occurred, then prune back to that level.

Q: I have a small orange tree that is about four or five years old. Two years ago, it had beautiful flowers. At the time, I didn't know about shaking the pollen onto the pistil. After finding that out, I waited until the next year, but it hasn't bloomed since then. Last year, it lost most of its leaves until I put it outside when the weather got warm enough. Does that have anything to do with why it hasn't flowered in two years? (e-mail reference)

A: As a houseplant, orange trees tend to be somewhat fickle. Sometimes they flower but don't set fruit. Sometimes they don't flower but do grow rampantly. Basically, one has to select a variety that is known to set fruit indoors. You might be overfertilizing with too high of a nitrogen source. If so, I suggest not fertilizing for a while. Definitely summer the plant outdoors and bring it in during the winter months. A refoliation is normal when the plant is moved outdoors. During the winter months, you probably had the plant in a draft of cold air or it was impacted by a forced-air system. The tree also could be responding to the extremely dry indoor air that is a characteristic of homes during the winter months.

Q: I have a problem with my hollyhocks. Each spring, they look fine and then something causes the leaves to begin to look like lace. Some master gardeners did not have an answer for me. Would insecticidal soap be worth a try? I don't see any aphids, spider mites or anything else on the leaves. (e-mail reference)

A: This sounds like the activity of hollyhock weevil larvae. The adults have a long snout that is characteristic of weevils. The hollyhock weevil is related to the cotton weevil. They feed by inserting their snout into the unopened flower buds. They can have several generations in a single growing season. They often reside on the underside of the leaf so they can eat in relative quiet and safety. To control this pest, I would suggest using a systemic insecticide that contains Imidacloprid. There are several versions on the market. Be sure to follow the label directions.

Q: I bought a house last year with a not very well maintained apple tree. I was attempting to prune it when I noticed that it had quite a few branches with cracked bark. Some branches have lost most of their bark. I began to remove these branches when I discovered what appeared to be a codling moth caterpillar inside one of the branches. However, I think it must be too early for them because the tree hasn’t budded yet. The only other idea I can come up with is that it might be a borer of some sort. The caterpillar produces silk, which is why I don’t think it is a round-headed apple borer. (e-mail reference)

A: It definitely is not the round-headed apple tree borer. The tree is in pretty bad shape judging from what you describe, so I bring to question the wisdom of attempting to save it. When I've come across trees in that kind of shape, I advise complete removal and replanting with a new cultivar so you will know what kind of fruit it will produce. Getting rid of entrenched borers like this would involve using very toxic insecticides.

Q: I'm having trouble with my tomato plants. They are turning rotten on the bottom as soon as they start to grow. What am I doing wrong? Can you help me? (e-mail reference)

A: The tomato plants have blossom end rot. This is a common problem on the first tomatoes to ripen. The subsequent crops will or should be mostly free of this malady. It is caused by a shortage of calcium in the developing cell walls at the blossom end. It is brought on by fluctuations in watering or rain patterns and the fast growth on an underdeveloped root system.

Q: We have several walnut trees that are more than 50 years old. We get lots of walnuts but they have had worms the last few years. Do you have a solution? (Iowa)

A: These worms are the larval stage of a small fly known as the walnut husk fly. Several species exist but their damage and control is the same. You should clean up and destroy any fallen fruit and foliage. Place some pheromone and sticky traps to monitor the arrival of the pest. Contact the Entomology Department at Iowa State University to get specific information on how to control the problem. Spray the trees with Malathion insecticide after blossom drop. Do so when the temperatures are going to be below the mid-80s for a few days to avoid spray damage. Repeat the spraying in 10 to 14 days.

To contact Ron Smith for answers to your questions, write to Ron Smith, NDSU Department of Plant Sciences, Dept. 7670, Box 6050, Fargo, ND 58108-6050 or e-mail

NDSU Agriculture Communication

Source:Ron Smith, (701) 231-8161,
Editor:Rich Mattern, (701) 231-6136,
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