Hortiscope

July 6, 2006

Hortiscope

Ronald C. Smith, Horticulturist
NDSU Extension Service

Q: I have a few varieties of weigela that have beautiful, deep burgundy foliage. Last season I noticed that the foliage started to fade and became a dreary color by the end of summer. I want to prevent that this season. Is it nitrogen deficiency? Is this common? What do you suggest? (Minneapolis, Minn.)

A: I suggest checking to be sure they are not planted too deeply or have too much mulch covering the roots. If that is not the case, then I would suggest a soil test. Check primarily for pH and soluble salt levels. If those are normal, then check to see if the plants are getting added reflected light from a building surface. This is all assuming that you have not observed any insect activity from aphids, scale or spider mites.

Q: I have a chokecherry tree in my yard and have noticed that the fallen berries from last year have started blossoming. How do I get rid of these little saplings? (e-mail reference)

A: I'll bet a nickel that those are suckers coming up from the roots and not new seedlings. You can check this out by tugging on a few. If they are seedlings, the suckers will pull up easily. If not, you will see that they are attached to a root. You can get a material known as "Sucker-Stopper RTU" at a garden store. After pruning off the suckers, spray those spots with this material. You should not see suckers again for the rest of the year.

Q: We had a landscaping company plant some tree rows for us. How often do the trees need to be watered? The trees are Ponderosa pine and ash. We also have a single row of lilacs running along the front yard. (e-mail reference)

A: Are you talking about a dozen trees or hundreds? The best way to water is by drip irrigation. As to frequency and duration, it depends on the water-holding capacity of the soil, exposure and if the plantings were mulched. The goal is to keep the root zone moist, but not wet. All three species of plants will not do well if their roots stay in saturated soil too long. If you are making reference to just a few trees and shrubs, then simple hand watering two to three times a week should be more than enough, even under the most severe heat conditions, unless they are planted in pure sand.

Q: We planted two honeycrisp apple trees last year. Both trees are blossoming this year. Should we allow them to bear fruit (assuming these blossoms turn into apples) or should we remove the apples when they form? (e-mail reference)

A: Let nature take its course. Most likely, the trees will bear only a few apples. Generally, trees that overproduce will self-abort the embryonic fruit that is about pea size after the flower petals drop. If by chance they come on heavy, then certainly pick off most of them because that much weight can be physically and physiologically damaging.

Q: I read your answers to questions about pruning crab trees. I just want to be sure I understand your answer about the timing. You said early spring, so that means before flowering. Will the trimmed branches blossom? (e-mail reference)

A: You are correct. Early spring means before the trees bloom or leaf out. The remaining branches should produce a nice show of flowers, unless the pruning was very severe.

Q: My garlic and sweet red onions are always very hot! I don't mind the heat in my garlic, but would like to grow a sweet onion. Is it my soil or am I missing something? (e-mail reference)

A: It could be your soil, cultural practices, wrong cultivar of onion or location.

Q: I planted some petunias, but many of the flowers have lost their color. The flowers have white splotches and some seem almost completely bleached. Any thoughts? (e-mail reference)

A: It could be due to very high salts in the soil. Have the soil tested. If that is the problem, dilute it with generous amounts of sphagnum peat moss.

Q: A lady in our county is wondering what she can use to control worms in her onions and cabbage. With Diazinon off the market, can Malathion or Sevin be used on the cabbage to control worms? Can Dipel, Biotrol or Thuracide be used on the onion maggots? (e-mail reference)

A: Sevin is the better choice for onion maggots and can be used to control cabbage moth larvae. Dipel can be used on cabbage, but needs to be applied frequently and is slower acting.

Q: One of my irises developed root rot this spring. I have destroyed it, along with as much of the soil as I could. What should I put in the soil to prevent this from reaching other iris plants? They are planted 15 to 18 inches apart. I had this problem in a different part of the yard about 20 years ago. I think there was some sort of powder that I worked into the soil. I don't want to lose my iris plants because they are special plants that I spent a great deal of money on last year. I hope you can help me. (New Salem, N.D.)

A: You can use a fungicidal drench of Subdue, Terrachlor, Fore, Formec (mancozeb) and even Funginex. Powdered sulfur mixed into the soil also will help thwart root rot and other diseases.

Q: I have consulted a reputable mail order nursery house about the name of an invasive weed creeping in my lawn, but it could not help me. This weed is shaped like a shamrock and very dark green in color. The weed killer I applied in early spring didn’t work. Can you tell me what product I can use to get rid of it? (e-mail reference)

A: The weed is oxalis, which is a very persistent weed! It can be taken out with Trimec. Try to locate some at a garden center and follow label directions.

Q: I am a teacher and give the babies from my spider plant to my students for good effort in the classroom. They love it. I am moving to an elementary library position next year and do not have a window for my plant. Is there a way I can keep my spider plant alive in the library? (e-mail reference)

A: Keeping the fluorescent light bulbs fresh each year is a good start. Also, you can get plant lights that can be directed at the plant for about 14 hours a day (use a timer). That should keep the plant producing new offshoots.

Q: I've had a question about Russian sage. I'm not that familiar with the plant other than what it looks like. Can it be trimmed and when is the best time to do it? (LaMoure, N.D.)

A: Russian sage should be cut back in early spring. Leave 3 to 4 inches of growth.

Q: After the snow storm we had at the end of April, a lot of trees were left with broken branches. Should something be put on the wounds to prevent insects and diseases? Also, I have a tree shelterbelt. I’m having problems with the spruce trees. I had the soil tested and everything checked out OK. Some of the trees grow to a certain height and then topple over. Years ago there was a pig barn near the site. Could it be that the runoff from the barn has affected the soil? It seems to me that when the tree gets older and the roots reach a certain depth, something is getting to them. (Bowman, N.D.)

A: You do not need to put anything on the tree wounds. The trees should heal on their own, but be sure to make the proper cuts back to the trunk. The spruce trees may have a disease. Check the needles for spores. You may have to look at the needles under a microscope. If the trees are Colorado blue spruce, they are very susceptible to disease.

Q: My family purchased two honeycrisp apple trees for me on Mother's Day. We have not planted them. Where is the best place in the yard to plant them? We have no trees in the backyard. Can we plant two honeycrisp or do we need a different variety for pollination? Our neighbor has two apple trees of a different variety. How far apart can trees be planted and still be able to pollinate each other? We have a crab tree in the front yard. Is that too far away from the honeycrisp? Do you have any suggestions on how to prepare the soil? (e-mail reference)

A: Plant the trees where they will get full sunshine. With the neighbors having different cultivars of apples, you can plant as many honeycrisp apples as you want. Dig the hole wider than deep. Don't plant too deeply, just get the crown covered. Water the trees in well and keep the soil moist through the summer.

Q: I read your column religiously. Would you recommend using Ponderosa pine needles as mulch in perennial beds? Last summer I visited the botanical gardens in Cheyenne, Wyo., and observed they used pine needles as mulch. Also, when dandelions are sprayed or mowed, the blossoms still appear to go to seed. Are those seeds viable? I hope not. (Carrington, N.D.)

A: Using pine needles as mulch is a very acceptable practice. Unfortunately, dandelion seeds are very viable. Thanks for being a regular reader!

Q: I have extremely hard water. I’ve heard that when watering my trees and shrubs, I should never get the leaves wet. Is this true? (e-mail reference)

A: Hard water will leave a deposit that is unsightly, but not lethal to the plant. If built up too much, the deposits can inhibit photosynthesis, which may result in plant stress or growth reduction. Other than that, watering outdoor plants with hard water should not be a problem.

Q: Is there anything I can do if my tomatoes have too much nitrogen? I have blossom drop. (e-mail reference)

A: Nitrogen is leachable, so double water a few times to see if that helps. Flower drop also is caused by extremes in watering regimes, temperature swings or root damage.

Q: I’ve got a pest problem. I have pepper plants that have lost leaves from the bottom up. I know we have rabbits (we have a dog that usually scares them away), but I’m surprised that such small nips have been taken and so low to the ground. I thought rabbits decimated plants. Up until today, the plants were being eaten from the bottom up, but I noticed that one of the top shoots on a plant had been eaten. I haven’t noticed any other pests and my tomatoes haven’t been touched. (e-mail reference)

A: The problem could be caused by cutworm activity or possibly slugs. The photo you sent of a plant prostrate on the ground is a good indication of cutworm feeding.

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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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