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Ron Smith answers questions about plants, trees and gardens.

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I have a green ash tree that has roots that seem to be taking over my yard. If I have it cut down, how can I be guaranteed that all of the roots will be destroyed? (e-mail reference)

A: I can assure you that you will not destroy all of the roots. Only the flare roots around the base of the tree will be destroyed. The long lateral roots will remain and continue to sprout. To control this sprouting, treat the roots as you would any broad-leafed weed with an appropriate herbicide, such as Trimec or any similar product available on the market.

Q: We planted a limber pine extra blue in 2007. Unfortunately, we noticed that during the winter, a rabbit (or other pests) ate the needles off the lower part of the tree, but the branches are still there. Will the branches produce more needles? We also have noticed that these pests have eaten some of our lilacs. Will they survive? (Bismarck, N.D.)

A: The bare branches will not produce more needles. Sorry! As for the other plants, it all depends on what you mean by eaten. Girdling or eaten from the top down to the snow line? If the former, the plants may be doomed. If it is the latter, they will come back. I'd suggest waiting until buds break this spring to see what, if any, growth you get. This fall, I would suggest that you get a varmint repellent product. Apply it before and during the winter months. In Fargo, this is a full-time battle, so you can't let your guard down one bit!

Q: I have a hedge of caraganas. I collected some of its seeds to start more. I have kept the seeds inside. Do they need to be frozen before planting the seeds in pots? If so, would a few days in my freezer do? (e-mail reference)

A: If the seeds were mature and viable when you harvested them, sow them in the soil outdoors. They should germinate. No cold treatment is necessary.

Q: My heritage birch tree received a little fire damage to its bark up one of the three main trunks. The damage was mostly on the loose, curling exterior portion of the bark. I don't think there was damage to the main bark. The tree’s exposure to the fire was less than two minutes. Parts of the trunk have turned dark, with a sort of mix of surface ash and nonburned loose bark. Will it live? Will it recover? (e-mail reference)

A: I would like to believe it will recover, but not without scarring. Wait to see what new growth there is this spring.

Q: A few years ago, I bought some Himalayan birch seeds and planted them. As I understand it, this type of birch should have white bark. However, the trees these seeds produced have a brown bark. Do you know if the white bark develops through time or is there something wrong? (e-mail reference)

A: You probably have nothing to worry about because many white bark birches have juvenile bark that is tan. As it matures, the bark turns a nice, chalky white. Be patient and see what develops. The Himalayan birch is a beauty, but not that common in landscapes.

Q: I heard that some trees grown from seed may not have the same characteristics of the parent tree, so I am worried. One of the trees I grew from seed is now about 8 feet tall, but still brown. Do you think this is normal? (e-mail reference)

A: While seedling variation does exist, unless there were other species of birch planted nearby, the variation would be minimal. You tree still is considered a juvenile, so the brown color is normal. It should start to whiten for you in a few more years.

Q: I just planted a winding willow tree in my backyard. I made sure to place it well away from the septic tank and drain field. I ran an irrigation system to it and buried two 1.5-inch PVC pipes drilled with holes in them to feed water down to a depth of 2.5 feet. I hope this encourages the roots to grow. I am wondering how much water it needs. I plan to water it every two days for an hour until it is established. Is this too much or too little water? When should I cut down on the watering? (Rio Rancho, N.M.)

A: I think you mean a weeping willow because I've never heard of a winding willow. Don't worry about overwatering the tree because it will take all that you give it. However, you do want the roots to expand so that the tree will become wind stabilized. Depending on the soil type and its ability to hold water, you may want to stretch the time between waterings by a day or two to allow the roots to follow the percolating water. Generally, after the initial year of getting the tree established, you should not need to provide any more water unless there is an extended period without rain or you are growing the tree in sandy soil.

Q: I have two flowering crabapple trees in my yard. I hit one of the trunks with the weed-eater and knocked some of the bark off. Will the tree die because of this? What should I do about it? (e-mail reference)

A: Put a ring of mulch around the trunk of the trees to keep you from nicking it with the string trimmer. The tree will recover on its own if it is vigorous enough. Other than cutting off any loose bark back to where it is attached, do nothing else.

Q: We recently removed a wild cherry tree stump from our yard. We were told the remaining part of the stump would rot away. We also were told that we would not be able to plant flowers in this spot because the tree put something in the soil that would not allow flowers to grow. Is any of this true? (e-mail reference)

A: It’s not entirely true. If they left sawdust from the grinding, as some do, it could inhibit the growth of the flowers or vegetables because it ties up the available nitrogen by the soil microbes until it is "weathered" enough. To solve this problem, remove as much of the sawdust as possible and replace it with fresh soil from another part of your yard or with some you can purchase from a garden supply store.

Q: I purchased a subzero hibiscus. However, I’m not sure if this particular variety needs to be brought indoors during the winter months. I live in zone 6. (e-mail reference)

A: It is rather late to be asking this question. I would think so, but I never have heard of a subzero hibiscus. Zone 6 winters are so mild that I can't imagine that a plant dubbed "subzero" would be vulnerable to anything one of your winters could throw at it.

Q: I am looking for certain types of trees or bushes that will hold well on a hill and have a vigorous root system. The hill is somewhat steep and the trees or bushes will be used for support. Looks are not hugely important. I also am looking for something that will not require too much water. These plants will receive a lot of direct sunlight. (Omaha, Neb.)

A: The best species for covering slopes is Rhus spp., which commonly is known as fragrant or staghorn sumac. Both spread and fill in an area quickly. The fragrant sumac is the more sophisticated of the two. The staghorn is the more dramatic. I would interplant these with native prairie grasses, such as big bluestem or some ribbon grass. Both are rhizomatous and fast spreaders. Also, don't overlook the common lilac. While not as aggressive as the sumac in spreading, the common lilac does get quite an extensive and suckering root system that will help hold the soil. As for trees, consider those that are used in shelterbelt plantings, such as cherry, apricot, plum or whatever is available in your area. I don't know how large a slope you are talking about, but if it is at all extensive, you might want to contact the Soil Conservation Service to see if it has plant material available and more regional suggestions.

Q: I live in Bellevue, Wash. I bought a pot of red and white tulips. Should I water them every day? It is overcast most of the time, so should I keep them in the house close to a window or put the plants outdoors? They are drooping a little. (e-mail reference)

A: They probably are in a potting soil or gravel that has excellent drainage, so the tulips probably could tolerate a shot of water every day. Tulips are cold-hardy plants, so they can be placed outside at this time of year. I assume you purchased them to enjoy their visual beauty, so keep them where you can enjoy seeing them on a regular basis. To keep the flowers around longer, place them in the coolest place in or outside of your home at night when you go to bed. Bring them out again the following morning.

Q: I have a great little bunch of rock tulips that come up every year. They have great foliage and nice blooms, but each year the blooms are less and less red. This spring, they have lost almost all their color. What do they need? (e-mail reference)

A: Nothing that I know of. This occurs when the tulips acquire a virus or the color is a chimera that reverts to the original color. The only thing I can tell you is to appreciate what they have become or replace them with the color you want.

Q: My goldfish plant is quite large and old. It has runners that are up to a foot long and quite woody. We live in western Colorado where the climatic conditions are very desertlike. The plant blooms well in the summer and fall months. For the most part, its leaves are glossy and healthy. It was repotted two years ago and is free of insects. My concern is that the older runners are dropping many leaves. Some of them are almost void of foliage. The leaves that are dropping are mostly brown or pale green and soft, but some of them appear to be healthy. There is abundant, healthy new growth in the center of the plant and some of the woody, older runners have new growth. What should I be doing for this critter? Should I prune back the older growth? I have not let the potting soil dry during the winter months. Could this be part of the problem? I never have misted the plant, but it seemed to be doing OK without that. (e-mail reference)

A: I think your initial problem is in keeping the potting soil moist through the winter months. Like many tropical plants, this plant benefits from a drying down during the winter. Allow the soil to dry almost completely and then give it enough water to moisten the soil completely. Pruning also would help. While at it, use some of those healthy prunings to propagate new plants. You've probably gone beyond the normal life expectancy of this columnea as a houseplant. A normal range is three to four years. That’s why propagation is encouraged. Like humans, plants change as they age and often not for the better. When this is realized, some changes need to be made, such as repotting, adjusting the watering cycle, relocating or simply taking cuttings to perpetuate the plant.

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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