October 19, 2006

Hortiscope

Ronald C. Smith, Horticulturist
NDSU Extension Service

Q: I read your article about digging out plants and then using Roundup to get rid of unwanted mint. Does that mean I have to dig up everything, including my rose bushes? (e-mail reference)

A: Mint is very vulnerable to Roundup. You can approach your problem a few different ways. Protect the plants you want to save by placing a plastic bag over them when you are spraying with Roundup or remove the plants you want to keep that are above the soil surface and spray the Roundup to your heart's content. Since Roundup is not soil active, it will not affect the bulbs as long as there is no green foliage showing.

Q: We have 11 potentilla plants in one section of our landscape. I think the plants are too close to each other because they are growing together to form a triangular hedge. My wife wants me to remove about four of them and space the others. Is this possible without killing them? (e-mail reference)

A: Wait until they go dormant after a couple of good killing frosts. You can do it this fall or early next spring before the buds break.

Q: I have a co-worker who is battling voles in her yard. Does the master gardener have any suggestions on what to do? She's resorting to what I term voodoo measures (pinwheels in the burrow holes), so she would welcome any suggestions you might have. Thanks for your great advice on just about any topic! (Turtle Lake, N.D.)

A: It’s not voodoo or black magic, just basic science! I have several scenarios you can choose from. Habitat manipulation means keeping the grass mowed, especially around trees. Remove brush piles or piles of unwanted yard or construction material where they can hide. The lack of cover will make them vulnerable to raptors, such as hawks and owls. Poisons, such as zinc phosphide and other commercially produced anticoagulants, are available. The poison comes as bait and is most effective when used in the fall and again in early spring. As with any poison, handle it carefully and follow label directions. You also can use live traps. Place the traps in the voles’ runways and cover with a piece of cardboard. Peanut butter is an excellent attractant. Release them as far away from your home as possible, at least 1/2 mile.

Q: We have a hedge of dogwoods that are overgrown, so we need to prune them to the ground. Can we do it this fall or should we wait until spring? Also, I need to move some rhubarb. Can I do that this fall or is it advisable to wait until spring? What kind of soil amendments should we use? I have a morden sunset rose that had a bad case of black spot this summer and now has very few leaves. Can I cut all the canes down to about 6 inches and clean up all the mulch and leaves or is it a lost cause? (Cooperstown, N.D.)

A: You can cut the hedge back in late fall or early spring, but before new growth begins. Fall usually is preferred because the working conditions are better. The same holds true for rhubarb. Always add sphagnum peat moss because it will never hurt and always helps. For your rose, do the cleanup and next year use a systemic fungicide to control black spot.

Q: What is the difference between a water plant and its landlocked cousin? As an example, I purchased water canna and then was told that standard canna could be used in a pond the same as water canna. Is this true and can it also be said of calla lily and iris, or do you have to purchase the specific water calla lily or water iris? (e-mail reference)

A: First, I'll have to admit that I am not an expert on aquatic plants, but I doubt that the same canna that is used in landscaping can be used as a pond plant. The same goes for the other two you mentioned.

Q: I have a few birch clumps that are dying on top. They could be river or paper birch trees. Last year we cut a portion of the top off on one tree in an effort to save the tree. That tree in the clump seems OK this year, but the top on the other is looking a bit thin and has smaller leaves. Any treatment you can share with me or is this the slow death of a birch tree? We did spot some holes around the girth of the tree. Is this the borer we have read so much about? (Carrington, N.D.)

A: Unfortunately, it is borers. You can attempt to save the tree by applying the Bayer product that has been promoted on the market. It is a systemic that moves through the vascular system and kills the borers as they feed. It is too late for this year, but you might be able to save the tree next year with an application. It has to be a judgment call on your part. If the damage has been too extensive, you might be better off taking the tree out.

Q: I enjoy your gardening column. I have received a lot of good information, but as yet no one has asked about how to get rid of horseradish. We have kept it at one end of the garden, but it has spread across the whole end. We’re thinking of getting rid of it, but we’re not sure it’s possible. We keep digging it up, but it just keeps coming back. We seem to be breaking the roots, but not getting them all. Do you know of a way to get rid of it? Thank you so much. (Lisbon, N.D.)

A: Other than digging out as much of the root as possible and scalp mowing anything that emerges in the next couple of seasons, all I can suggest is the use of a chemical weed killer, such as Trimec or Roundup.

Q: I have two fern peonies. Every year they keep cutting them off at ground level at the cemetery. Does that hurt the bark for next year? (Langford, S.D.)

A: If the foliage is removed early in the growing season, it will weaken the plants and reduce their flowering ability.

Q: I am always fighting grass growing in my irises. What can I use to kill the grass and not destroy the irises, and where can I get the product? (Ada, Minn.)

A: Look for a grass control product that contains sethoxydim. There are several on the market. If label directions are followed, the product will selectively take out the grass without harming the iris.

Q: I have a Haralson apple tree. I usually wait until after a light frost to pick the apples. Now I hear from some people that you should not wait that long. When should I pick the apples? (e-mail reference)

A: Pick them when they taste good to you. Waiting for a frost is not necessary.

Q: We want to establish a hedge/windbreak on the east side of our property. Can you suggest something that would produce berries for the birds and be trimmed to form a nice hedge? Is there something we can plant that will produce fruit that people can eat? (Napoleon, N.D.)

A: If it is edible for people, it definitely will be edible for birds as well. You might as well forget getting anything for yourself. A few suggestions are cotoneaster, honeysuckle and viburnums.

Q: I have box elder bugs on my flowers. How can I kill them? I have been using Malathion Plus, but it seems like there are the same number of bugs the next time I look. I have tried spraying on the house, but the bugs still come in. I also have lady bugs or bean bugs and stripped flies. (Nome N.D.)

A: You are better off hiring a professional pest control company. The Malathion should be doing the job, but the company can lay something down that will last longer.

Q: I am having a problem with some of my house plants. I noticed one of my spider plants started getting a little wilted and then started dying. Even though I didn’t see any bugs, I sprayed it with Safer Soap. It kept dying, so I put it outside for a couple of days. It showed no signs of improvement, so I dug up one of the rotted roots. I found tiny, almost translucent worms. Is there anything that will kill the worms quickly before there is no plant left to save? Any help you can give me would be appreciated! (e-mail reference)

A: Wash all the soil off the roots and dispose of those that are not functional. Repot with fresh potting soil that is marked as sterilized or pasteurized media. Repot in a container that is free-draining. If there is any hope, this should save the plant.

Q: You mentioned that a good fertilizer combination for grass is 20-8-3-6. Where do you purchase this combination? I have called green houses and other places, but have not had any luck. (e-mail reference)

A: That was just an example, not a real fertilizer analysis. There are plenty of good winterizer materials out there, such as 22-3-14, 22-4-11 and 15-5-15. Call one of the major outlets to find out if they have anything approaching that ratio.

Q: I have a question about buttercup squash that I grew in my garden this season. I live in the northwest part of North Dakota. My garden is under an irrigation pivot in the corner of an alfalfa field. The buttercup squash grew beside two other types of squash, spaghetti and acorn. My squash has white, raised spots that resemble seeds on the outside skin. The water that we irrigate with is high in sodium. What caused these spots? Is this squash safe to eat? Do I need to do anything special to the squash in order to make it safe to eat? (e-mail reference)

A: Those are corky lesions on the skin of the squash, which are nothing to worry about. The lesions will not affect the eating or storage quality of the vegetable. This comes mostly from physical damage, such as insects, hail or wind-blown dirt.

Q: I was given some black walnut seeds. I would like to learn how to propagate some of them. Do you have a bulletin that you can provide by e-mail or regular mail? (e-mail reference)

A: Sorry, we don't. You can allow Mother Nature to do the work for you by planting them about 6 inches deep this fall before freeze-up. The viable ones will show growth next spring, if the squirrels don't see you planting them and harvest them for food. These are difficult trees to transplant, due to their strong taproot development. I recommend planting the seed (for the most part) where you want the trees to grow. They take off fast in their youth and then produce slow to moderate growth as they enter maturity.

Q: I have a small orange tree in a pot. It is covered with small, reddish brown circular spots that can be wiped off easily. What sort of pest is this? The oranges the tree produces are green, not orange. Could this be related to the pest? (e-mail reference)

A: Those spots sound like scale insects, so keep wiping them off. As far as the oranges, you probably have a species that requires coloration through ethylene gas. This can be accomplished by harvesting mature, but green oranges and placing them in a bag of apples. Apples are good producers of ethylene. Do this at room temperature and the oranges should turn color in a few days.

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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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