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Ron Smith answers reader's questions about the world of plants and gardening.

By Ronald C. Smith, Horticulturist

NDSU Extension Service

Q: I bought a house with three large lilac bushes in back. The three are white, purple and reddish purple in color. They are beautiful, but I have severe allergies and asthma and believe they are aggravating my problems. How long do the blooms last? Can I remove them now? Can I prevent the blooms from coming back and still keep the bushes? (Denver, Colo.)

A: You can remove them now, with no harm to the plants. To keep them from blooming every spring, do an early spring pruning while the plants are dormant. If you do this, you will not get blooms that year.

Q: I bought a couple of Canada red rhubarb plants from a reliable source a few years ago. I deliberately chose Canada red rhubarb because I thought I would get rhubarb with red stalks. However, the stalks are green, not red. In the spring of 2006, I bought another Canada red rhubarb plant. I planted it in a raised bed and used a lot of organic material. The bed has good drainage and is in a location that gets morning sun and late afternoon shade. This plant also prospered and produced green stalks. I didn't remove any stalks last year, but I am cutting and using some stalks this year. I asked a plant specialist why I am getting green stalks, but he has no answer. (e-mail reference)

A: All I can guess is that the Canada red rhubarb is a clone that developed from a sport or chimera. When the grower divided the crowns for propagation and sale, the grower was unable to perpetuate the sport (the red stalks), so you end up with healthy, but green-stalked plants. Your best bet is to find someone who is growing red rhubarb and ask for a division. That way you are certain of getting the color you want.

Q: I am looking at purchasing two apple trees to put on our farm. Should we get the same trees (Haroldson) or get two different varieties? How far apart should they be? I do not have a green thumb. Thanks for your advice. (e-mail reference)

A: Planting two different types of apple trees is always better. How far apart you want to plant the trees is up to you. Bees will find the trees and do the work (I hope). The bees can do their pollinating work within a couple of hundred yards.

Q: Can you provide some advice on controlling tree suckers in my perennial flower beds? I'm constantly fighting tree suckers every year. I've attempted to be diligent and cut the suckers off below the surface, but I can't keep up. Is there something I can apply that will kill these little trees or woody plants and keep them from coming back? (e-mail reference)

A: The stuff I have used is called Sucker Stopper RTU. I have seen it at Cashman Nursery in Bismarck. The sucker is cut off, and then the material is sprayed on. It lasts for one growing season.

Q: What is the tree with the fragrant white flowers? They are growing all over in Grand Forks. I'd like to plant some myself someday, but don't know what they are. (e-mail reference)

A: The tree could be spring snow flowering crab, Juneberry or flowering pears. If you can pick a small branch from one of them and bring it to the Grand Forks County horticulturist for positive identification, you would know for sure what it is you want to purchase.

Q: I have a Haroldson apple tree that produces lots of apples. However, every year the apples are full of dents that look like small bugs of some sort. I never have had any good, clean apples from the tree. I did spray the tree last year, but it didn't make any difference. I waited until the apples had formed because I was afraid to spray while the tree was flowering. Was that wrong? Please help me. I love these apples and eat them anyway, but sure would like to have some clean, beautiful apples. (e-mail reference)

A: Spray the three with Sevin when the apple blossoms are just starting to fall and the bees are not active. Repeat the application about a week later. Pick up all the fallen apples from last year if you haven't done so.

Q: I have two peach trees here in Virginia. The past two seasons I've lost all of my fruit due to insects and borers in the tree and fruit. I've sprayed the trees with products provided by my local feed store. I've sprayed so much that last year the leaves turned brown and I almost lost the trees. This year the trees are loaded with peaches, so I don't want to loose this year's crop! I dug around both trees and found at least 20 black grubs near each tree. I also put down pine bark nuggets, which I was told would add acidity. I do not see signs of borers in the trees, but something is in the fruit. What do I need to do to eliminate both problems? (Southeastern, Virginia)

A: I strongly suggest that you make contact with the land-grant university in your state and seek out the horticulturist who specializes in fruit tree care or culture. If one is not available, the folks in the entomology department can get this problem resolved. You don't want to surrender those delicious peaches to those ravenous insects!

Q: We have wave petunias that are blooming and look ready to plant. The plants are in a small, farm greenhouse. We have noticed that some of the leaves are turning black, but have good texture. Thank you in advance for some help. (e-mail reference)

A: This sounds like a pythium fungus getting started. This is the same fungus that is related to seedling damping off. Increase the air circulation, avoid overhead watering and spray with a fungicide, such as Subdue, Maxx, Alude or Aliette. Hopefully, you've used sterile or pasteurized soil.

Q: I have an old cherry tree that has the best cherries I have ever eaten. The bark is peeling off in huge layers and the overall appearance of the skin is very rough. It has these gems on it that I've been told is the problem of whatever is going on. From talking to people locally and reading on the Web, I believe it is bacterial canker that has no known cure. These jewels are on the trunk of the tree, so pruning would mean cutting it down. Can you help me? Thanks. (Sacramento, Calif.)

A: If it is a bacterial canker on the main stem, then the tree is lost and you are better off cutting it down.

Q: I saw your column and am hoping you can shed some light on my poplar tree problem. We have an old poplar tree in our backyard here in Oklahoma. About 40 percent of the branches have leaves on them. The rest of the branches are bare and appear to be dead. The branches with leaves are at the bottom of the tree. One tree service has recommended we cut the tree down. It said poplar trees are prone to disease and insect infestation. Is there any truth to this? Is there a common disease or insect problem that would cause the tree to exhibit these characteristics? (e-mail reference)

A: Your local arborist is right about poplar trees. There is a text devoted to the problems these trees have. Just a few of the problems are borers, bark beetles, stem cankers, fungal leaf spots and vascular disease. Have it cut down and used for firewood.

Q: We planted a cotoneaster hedge 29 years ago. It got so rotten that we cut it down and put up a fence for privacy. We are wondering how to kill the trees that keep growing back. We keep cutting them off, but there must be an easier way. Please let me know if you have any helpful hints. (e-mail reference)

A: Roundup is perhaps the easiest way to control the new growth.

Q: I have two Medora and two Wichita junipers. They are doing very well. I think they are doing well because they are growing next to my house. I was considering a row of Medora junipers on the north side of my property. I would like to use it for privacy and a windbreak, so I would like a tight grouping, but still healthy. What kind of spacing would you recommend? (West Fargo, N.D.)

A: These native junipers would be the perfect choice for what you want. I would suggest 3-foot spacing for a tight fit.

Q: There is a large cottonwood tree on the vacant property next door. The owner of the lot cannot be located. I have a very large root growing in my yard and it is starting to compromise my pool. Is there a way to kill the tree from the root in my yard? (e-mail reference)

A: Rather than do that, I would encourage you to contact the city forester to see if there is a legal and safe way to have the tree removed. Perhaps you can get an "abandonment of property" declaration to get it done. If that is not an option, then get a contractor or arborist to cut the root back to the property line and then install a root barrier at that point.

Q: I live in central Scotland. My grandma moved here from the Scottish Highlands in the 1950s. She brought with her a cutting from her mother's lilac bush and planted it in her garden. It flowered beautifully until about 15 years ago. Unfortunately, my grandma passed away last year. In her memory, I would like to grow a lilac bush in my garden from a cutting taken from her lilac. Will it grow even though the original bush has not flowered in years? What is the best way to go about growing it? Thanks and best wishes! (e-mail reference)

A: Lilac cuttings easily root if taken in mid-June. The cuttings should be 8 to 10 inches long. Dip the cuttings in a rooting hormone and then stick them in a sand medium under mist. Lilacs characteristically develop a nice mass of roots.

Q: I am in college and just purchased a croton. A friend told me to only water it when the soil is dry, but the leaves look waxy and dirty and one of the leaves has a dry patch on it. Is there a way I won't kill it? (e-mail reference)

A: If there is such a thing as a tough houseplant, the croton is it! Your friend is correct in saying that you should water it only when the soil is dry. When you do water, make sure it is sufficient enough so that water flows out of the base of the pot. Allow it to drain for about 30 minutes before dumping the water out of the saucer. You can wash the leaves in the shower every now and then or you can wipe them with a wet cloth.

Q: I stumbled upon your Web site today as I was searching for information on maintaining Concord grapes. We just moved into our house. There are two fantastic grapevines in our yard that have to be at least 20 years old, but have not been maintained. We are brand new to grape growing, so we are hoping that you may be able to give us some advice on fertilizing, pruning and bird protection. We would appreciate any assistance! (Wakefield, Mass.)

A: Pruning vines on an annual basis is enough of a challenge, but yours is in the impossible area after looking at the photos you sent! I have no idea how to tell you where to begin. They are survivors, so probably anything you do will not kill the vines. All I can advise is to prune anything that is inconvenient for you or your movement around the property. After looking at the photos, you don't need to fertilize. Netting and scare balloons seem to work best to keep the birds away.

Q: It was very hot in San Francisco this week. Because of the hot weather, half of a large jade plant in the backyard collapsed. The day before, I noticed that the leaves were turning away from the sun. It was shaded by a tree that was pruned back, so the jade is in full sun. It is watered four times a week using an irrigation system. The fog has returned, so it probably won't see any sun for a few days. Any suggestions would be great. (e-mail reference)

A: My only suggestion is to wait and allow the jade time to adapt to the change in the environment. It may look terrible for a period of time and lose more leaves, but it should recover and return to vigorous growth.

Q: We purchased an autumn blaze maple from a tree farmer and had it professionally installed. Can I put up a retaining-type wall around the tree to use as a planter? How far do I have to stay away from the trunk? How high can I go? Your help would be greatly appreciated. (e-mail reference)

A: Forget the retaining wall and piling soil around the trunk because it eventually would kill the tree. You can plant under the tree's canopy without any problems, but if you bring in more than just a few inches of soil over the root system, you will have trouble.

Q: My grandma has had a problem with her tomatoes getting black spots and rotting a day after they are picked. Most of the tomatoes can't be eaten. She said she is rotating the plants. She also grows pepper plants. They are always good. She doesn't water with a hose or sprinkler. She uses a bucket and waters with a pan, so there is no splashing. (Springfield, Ohio)

A: It sounds like your grandma is using seed she saved from the previous year. If so, she should purchase fresh seed each year because many diseases can be carried over in the seed of infected tomatoes. If that isn't the case, then tell her to get hybrid tomatoes with the letters VFHNT after their names. These are tomatoes bred for resistance to the most common bacterial, fungal and virus diseases.

NDSU Agriculture Communication

Source:Ron Smith, (701) 231-8161,
Editor:Rich Mattern, (701) 231-6136,
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