July 13, 2006

Hortiscope

Ronald C. Smith, Horticulturist
NDSU Extension Service

Q: We have a weeping birch that was doing well. This spring, there was a large, dead branch that my husband cut off. Should the stump be sealed or tarred or is there anything else we should do? The tree has been treated for birch leaf miner. (e-mail reference)

A: There is nothing more to be done. I have an identical tree in my front yard. What killed the branch probably was bronze birch borer. Leaf miner seldom, if ever, is lethal to birch trees, but borers are. You might want to get the tree examined by an arborist to determine for sure that it was the borer that caused the death of the branch. If caught in time, treatments can be applied that will control the spread. You don't want to lose this very beautiful tree!

Q: I received a bright, pink-colored cyclamen, which did not do well initially. The flower wilted and the leaves yellowed, but these problems were rectified with less watering. The continuing problem is that the pink flowers turned white and the new buds also are white. Why has this occurred and is there anything I can do to bring back the vibrant color? (e-mail reference)

A: Not that I know of. This is likely a chimeral mutation that was lost, so it reverted back to its original color, which was white.

Q: I want to say that I enjoy reading your column. You seem to be helpful to a lot of people. I have a small orchard with 12 apple trees and a separate stand of four trees. I was careful to make sure I purchased the correct varieties in order to properly cross-pollinate. I fertilize the trees in spring and fall. I water them on a regular basis and prune every spring as needed. Some of these trees are as old as 12 and some as young as five. I have dwarf and standard trees. My problem is that none of these trees has ever blossomed. I tried stressing them, but that didn’t work. The trees are planted in very sandy soil in northern Wisconsin. I mixed some rich topsoil and compost with the sand when I planted them and occasionally put lime around the trees. Can you tell me why my trees aren't blossoming? I have crab apples and other wild fruit trees nearby that blossom every year. (e-mail reference)

A: Thanks for the nice comments. The apple trees may not be hardy for your zone. Flower blossoms have a lower hardiness level than vegetative buds. You may have overfertilized with a high-nitrogen fertilizer. The trees may be too young to blossom, but that wouldn’t hold true with the older trees. Other than that, I'm at a loss as to why they wouldn't at least bloom for you!

Q: I have a hosta that is looking really great, but I would like to move it. If I dig deep enough around and under the plant/bulb and place it in the same-sized hole, could it be moved without damaging it? It will remain in the same soil and flower bed.
(e-mail reference)

A: You should be able to move it successfully. Do it during the cooler evening hours and water it well after the move. Even if it does wilt, don't worry. In most instances, hosta will recover.

Q: We just bought a home with a lot of bushes along the side of the house. The branches were hitting our windows and were growing out of control. My husband trimmed a snowball bush. Since trimming, the growth is coming up from the bottom, but there is no growth on the original trunk. Can we fix the problem with additional trimming? When should we trim it? (e-mail reference)

A: Take out the original trunk or branch because it is probably dead or too old to send out new buds. Enjoy the flush of new growth coming from the base. The bush should flower next year.

Q: I have an old, large jade that I would like to prune. I have read your material, but I just don't get how to prune. Through the years, I’ve had great success repotting any leaf or small stem that has been cut off or dropped. After starting a new plant, what determines what size pot the plant should be put in? With existing plants, how can you tell if they are in the right sized pot? Is there a formula for figuring out pot size? Also, how do I get a copy of your “Home Propagation Techniques” publication? (e-mail reference)

A: The "Home Propagation Techniques" publication can be downloaded at
www.ext.nodak.edu/extpubs/plantsci/landscap/h1257.pdf. Regarding pot size to plant size, I'm sure someone in the horticulture world has come up with a formula, but I don't know what it is. We typically use that rare commodity called "common sense" in transplanting. If the plant is too large for the pot, it will appear unbalanced and very likely may be subject to tumbling over. If the water runs out of the bottom of the container when the plant is watered, then the plant needs transplanting. As the buffering capacity of the soil is lost or used up, you have close to 90 percent rootball mass and very little soil to hold the water. We generally recommend going up to the next nominal size pot when repotting, unless you don't want the plant to get larger in size. For example, you would move a plant from a 4-inch pot to a 5-inch size, but not from a 4-inch to a 12-inch pot. While on this subject, clay pots have different watering requirements than plastic pots. If you have been successful with one type, be aware of that fact if you change pot types.

Q: I have attempted to find information on how to prune a mock orange. We have a mock orange that was full of dead branches and twigs. The shrub also was outgrowing its space. It looked fine if you pruned it just right, otherwise you could see all the inner dead stuff. Last fall I hoped to return it to a lively looking shrub, so I tried to find information on how to prune. I should cut it to the ground as you have directed, but I very much appreciate the tree, so I didn’t want to kill it by overdoing it. I pruned the bush last fall after finding only one hint to cut it by thirds during a three-year period. This spring it looked awful. It was green on top with a lot of dead interior. It did have some sprigs from the bottom, but they were very unattractive. I read on your site to cut mock orange to the ground in early spring. Should I do this next year? I note you are in North Dakota, but I believe we are in a similar zone here in Saskatchewan. (e-mail reference)

A: We are in a similar zone. When plants get ugly, cutting them back to the ground will not hurt the plants if they are healthy and growing. Pruning in early spring, before growth begins, will force the stored carbohydrates from the previous season into the surging new growth. You won’t have flowers for a year, but you will have a handsome shrub. If flowering is an absolute necessity in your life, then allow what is there to flower. Prune the canes back to the ground immediately after flowering.

Q: I read about rust galls in your column. You mentioned that they were devastating to hosts, such as apples and Hawthorns. Do the galls have to come in contact with these trees to do harm? We have a new snowbird Hawthorn growing about 6 to 8 feet away from our low-lying juniper and a neighbor’s apple tree just across the driveway. Do you think we need to remove the rust galls? Also, will the galls affect an upright juniper? (e-mail reference)

A: Galls will use a juniper as an alternate host without causing any significant damage. Pick off the larger galls on the juniper and dispose of them. This interrupts their life cycle and protects trees, such as apples and hawthorns, from the more devastating form of the rust fungus.

Q: I purchased some lilac plants this weekend. Five are blue and two are white. I planted them about 2 1/2 feet apart. Is that far enough apart? I planted them to make a divider between my yard and that of my neighbors. My neighbors are very happy to have lilacs. I am, too, but I don't want them to look sloppy when they grow. (e-mail reference)

A: Two and half feet apart is a little too close because (assuming they are the common lilac) they can spread out to 8 or more feet. You might want to take out every other plant and transplant them somewhere else. You could leave the plants in place, but remove every other plant when they start to become crowded.

Q: What is the best solution for webworm problems? They are the insects that produce webs on trees and destroy the foliage. The person who called me had Sevin on hand, so I recommended that she try it. Is it a strong enough chemical to take care of the problem? (e-mail reference)

A: For the most part, Sevin will kill the webworms that are caught outside of the webbing. Malathion will do that as well, but it will leave a residual on the foliage that it covers. When the insect larvae eat the foliage, they will die. The best control is to spray trees that tend to become infested with dormant oil in the early spring before the leaf buds open.

Q: I have been told you cannot grow tomatoes and green/red peppers together. If so, how far apart should they be planted or should they not be in the same garden? (e-mail reference)

A: I haven't heard that and I've been growing them together for as long as I can remember with no dire consequences.

Q: I have a wild rose bush that is getting out of control in both width and height (12 or so feet high). How and when should I cut it back? Can I take my chainsaw and lop the whole thing down each spring or fall? Can I safely dig out some of the base of the plant? If so, could I possibly even replant the portions I dig out? (e-mail reference)

A: Go ahead and do some cutting on this monster. I promise it won't hurt anything. Every spring, cut it to the size you want and then some. Take into consideration the surge of new growth that will follow. Always cut just above a leaf or lateral branch.

Q: I had a lady call this morning with a peace lily problem. She has a brown ring on the leaf stems about an inch long and 1 to 1 1/2 inches away from the base of the leaf. (e-mail reference)

A: The lily is attempting to shut down after a winter of flowering and looking beautiful with the big, floppy leaves. Have her remove the affected leaves and back off on the watering until all the leaves are gone. Then barely keep the media moist for the next six to eight weeks or until new growth is observed. Resume the original watering cycle after new growth begins.

Q: My mom and brother have new plants that they want me to learn how to take care of. One is a sunflower and the other is a passion flower. How often should they be watered and how much water should I use? (e-mail reference)

A: If they are in containers, they will need different care than if they are planted outdoors.

Sunflowers, as the name implies, need full sun and about 18 to 24 inches of precipitation during the growing season, especially early on to get some growth started. Once sunflowers head out, the requirements for water are reduced. If you live in a temperate zone where freezing occurs in the fall and winter, the plant likely will be killed.

Passion flowers also like full sun, but cooler temperatures than sunflowers. This is more of a houseplant than an outdoor plant. For the summer, it would thrive outdoors in an eastern setting and the temperatures didn't get too high. It needs to be kept evenly moist during the active phase of growth, which usually lasts until early fall. Then back off on the water, but don't allow the rootball to dry completely.

Q: I was wondering if watering my tomatoes at night is OK. I also noticed that the following day my tomatoes start wilting again. Why? (e-mail reference)

A: Watering during the early morning hours is better. That way the plant can efficiently use the water with the warming sun and the chance for disease development is greatly reduced. The wilting during the day is a normal reaction as long as the soil is moist. The plants are probably getting full sun and/or reflected light off a light-colored surface. As long as the plants recover, you have nothing to worry about. The wilting will disappear as the plants mature.

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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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