April 24, 2003

Hortiscope

Ronald C. Smith, Horticulturist
NDSU Extension Service

Q: The leaves on my African violet are firm but are curling. Am I giving it too much water or sunlight? (E-mail reference)

A: Probably too much water. Be sure to water from the bottom, not the top and only about twice a week. African violets should never be put in direct sunlight -- bright indirect light, yes, but not direct sunlight. "Sun-burning" will occur. Check to see if there are any insects on the underside of the leaves. They can sometimes cause the symptoms you describe.

Q: I recently purchased a maiden’s blush lilac. The tag says it grows to be about 8-10 feet in height. I’m wondering how wide it will get because I'm trying to decide where to plant it. (E-mail reference)

A: It will get at least as wide as it does tall. Give it plenty of space. You've picked a beauty!

Q: Last year I asked you how and when to trim mugo pines but I lost the answer. I live in southeastern South Dakota. (E-mail reference)

A: Prune the new growth approximately 50 percent as it unfolds. If you want to reduce the size, then cut back to where there are still some needles or completely back to a lateral stem or branch.

Q: I have three blue arrow junipers approximately 10 feet tall and planted about six feet apart along the back side of a garage. How and when would be the best time to prune them? I would like to maintain their shape, but need to find a way to strengthen their trunks and maintain a manageable height. They are very susceptible to being whipped around by the wind; the tops sometimes droop and separate. (E-mail reference)

A: Try tying them up with cloth strips to give them support. Don't use wire or rope. Junipers respond well to pruning as long as it isn't overdone. However, you can prune the new growth almost all the way. Leave a wisp of green that parallels the branches you are removing. Whatever you do, never shear a juniper or arborvitae -- that literally ruins the natural form of these otherwise graceful plants.

Q: Is columnar buckthorn considered a host plant for soybean aphid? (Is it the same as other buckthorns?) We live on a farm and don't know if that’s a plant we should be using as an ornamental planting around the house, although we like it and have one nice established shrub. (E-mail reference)

A: Buckthorn is a host plant for soybean aphid so don't plant it unless you want to face the wrath of soybean farmers! It uses the buckthorn as an overwintering site in the egg stage.

Q: I am looking for information regarding my hoya plant. It is blooming right now. Sometimes it can have up to 16 blooms at a time. My daughter would like a cutting from this plant. When is the best time to take a snip and do I put it in water with a fertilizer or root starter or immediately plant it? Do I want to cut a stem that has flowered before? How long should I cut it? I have another hoya plant that has not bloomed. Both plants sit by a west window. The leaves on the one that flowers are quite faded and it looks like it may be root bound. On the one that doesn't flower, the leaves are dark green and it is not root bound. (E-mail reference)

A: Spring is the ideal time to take a cutting -- about 6-8 inches long -- from mature wood that is not currently flowering, and place it in a 50/50 sand/peat mix with no fertilizer. Keep it damp, not soggy wet. As long as the plant is producing flowers, I suggest leaving it alone. The same holds true for the one that is not flowering. Hoya should only be repotted when absolutely necessary.

Q: We heard or read there is a product that you can incorporate into the soil to control Colorado potato beetle. Is there such a product? Spraying is a labor intensive project and, in a large plot, time consuming. Also, what is Bt? (Ashley, N.D.)

A: Bt-bred potatoes are a thing of the past, thanks to the near maniacal hysteria over genetically bred food crops. They worked beautifully when we planted the Bt-enhanced potatoes next to the non-Bt potatoes. It was as if a wall existed between the two plantings. At first Bt potatoes were taken off the consumer market because they never really gained much of a market share. When the hue and cry reached a fever pitch, they were removed completely from any source - consumer, commercial, or research. Now we are back to the near stone age method of spraying or picking off beetles by hand. Bt or Dipel are the materials that you can now purchase to apply on the potatoes. They have the same effect as the bred-in material did, except that you must apply it repeatedly, every 10-14 days, to get control. They are safe for warm-blooded animals and environmentally friendly. Bt (Bacillus thuringiensis) is a naturally occurring bacterial disease of insects. Dipel as well as Bt, are the manufactured forms of this active ingredient. These materials are also very effective against leaf and needle chewing caterpillars and certain beetles. These products can be safely used on essentially all food crops.

Q: We're growing some tomato and pepper transplants. Some of the tomatoes are showing strong purpling of the leaves with the veins remaining green. They are growing in small 1 1/4 inch size plug trays. Their about 6-7 inches tall. Would adding some Miracle-Gro help? Should we transplant them into something larger? How about the temperature? The temperature they are being kept at is around 60 degrees. (Cando, N.D.)

A: The temperature is too low, there is not enough soil mass, and they are suffering from lack of nutrients. Raise the temperature to about 70-72 F., repot into larger containers or packs and fertilize every two weeks with a complete fertilizer.

Q: I don't have a very green thumb, but I somehow manage not to kill most hardy plants. I've had a large, 4 foot, schefflera for about five months but lately it seems very sick. It originally got a lot of big brown spots, then the leaves started falling off, and now the leaves that are left are quite translucent. It's never been repotted and I don't use fertilizer. I've read that feeding a sick plant can be bad. (E-mail reference)

A: You didn't tell me where in the house you have the plant located. It sounds like it is suffering from too little light combined with some over watering. I would suggest you move it to an area with more light, cut it back and water only when the soil is dry. If it starts responding with new growth, then begin fertilizing every month. If nothing happens after six weeks, then dump it -- the poor thing's over the hill!

Q: I have some wave petunias that I am growing under flourescent light. They are about six weeks old and are nice stocky-looking little plants. The light is on them about 15 1/2 hours a day and I fertilize about once a week. Recently some of the leaves started turning yellow. I had the same problem last year with my geraniums. I water them when the soil feels dry. (E-mail reference)

A: I suspect that the soil may be poorly drained or that you have them in containers that are not free-draining. I am assuming that you are using pasteurized soil media that you purchased at a local garden store. If you have done all of these things, then it could simply be mature leaf senescence.

Q: My husband and I planted six arborvitae last summer that looked great. This spring we have noticed that the bottom foliage has turned black. It almost looks like black spray paint or tar. It is on most of them and goes up the tree about 12 inches. They are planted right next to a field where corn and beans are planted and fertilizer is sprayed. I wouldn't think that would be the problem. (E-mail reference)

A: I would suggest taking a sample to a plant diagnostic lab at your local land grant university. There are just too many things that could be causing your problem for me to try to answer in this column.

Q: I have two beautiful apple trees in my backyard, however my husband does not like the mess they make every year. Is there a way that we can keep the trees and not have any apples grow on them? Is there a chemical or something we can put on the trees to stop the apples from growing? (E-mail reference)

A: I sympathize with your husband. Unfortunately, there is nothing that is dependable enough on the market to recommend.

Q: I have a dracaena marginata that is about 3 feet tall with a very thin cane. It appears to be healthy but it is not strong enough to stand upright alone. Should I use a stick to support it? (E-mail reference)

A: You can but I would look to the future and consider making that spindly cane into several propagules, which are called Ti trees. Cut the cane into 3 inch sections and insert the end closest to the roots into a rooting medium. Be sure to keep it moist. These pieces will eventually root, then you might get new, stronger growth coming from the mother plant. You might try providing that new growth with more light -- near an east or west window.

Q: We are planning on planting 100 feet of American arborvitae along our property line this year. How much growth can we expect each year? Can they survive in our area which is zone 3 in Canada? What is the best time of year to plant? ( Edmonton, Alberta, Canada)

A: The American arborvitae cultivars techny and Brandon are the hardiest, showing the most resistance to winter burn. They should do all right in your area, as long as you spray the foliage with an anti-desiccant prior to winter's arrival. Both are hardy down to -40 degrees F. (zone3).

Spring is best time to plant them -- whenever that arrives in your part of North America.

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