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Hortiscope

Ron Smith answers questions about the world of plants, trees and gardens.

By Ron Smith, Horticulturist

NDSU Extension Service

Q: Do rabbits or squirrels like eating marigold flowers? If so, is there something I can do or spray on them to deter this? (e-mail reference)

A: Get some pepper spray. It will stop them from going beyond the first nibble.

Q: How do you prevent a rose of Sharon bush from dropping its seeds? I have about 100-plus new bushes coming up, but I don't know why. (e-mail reference)

A: This is a problem with this species of shrub. Self-sowing is a common, annoying problem. Unfortunately, there is not much you can do to prevent it. They easily are controlled with shallow cultivation or selective treatment with RTU Roundup.

Q: I have no idea who to ask about this because the nursery that I got a weeping willow tree from seems to know very little about them. I got it late last year. The leaves turned yellow and eventually fell off. So far this year, it has not done much. I would love to plant it outside, but I read on your Web site that the roots are very invasive. Will it live if I keep it in the house? I really like it, but I don't want any waterline or foundation problems. Any advice? (Ontario, Canada)

A: It will not last as a houseplant. It needs to go through the seasonal changes to amount to anything, so plant it outside. If you don’t have any leaks in your foundation, water or sewer line, it will not be a problem.

Q: Our dog tore or ate the bark off our beautiful crab tree last week. The dog removed the entire bottom around the base of the tree up to the branches. We have been told by several older folks that we probably will lose the tree. However, we are hoping you might have some insight to help us save it. It gives us many delicious apples each year. Any advice you can give us would be great. (e-mail reference)

A: If the bark is removed all the way around the tree, the tree essentially is dead. The older folks delivering the message are correct. Sorry, there is nothing you can do.

Q: When harvesting rhubarb, do you cut with a knife near the soil or do you pull firmly at the soil level? Are we both right? (e-mail reference)

A: It is accepted to simply twist and pull the stalks or cut them. It boils down to nothing more than whatever is most convenient for the harvester. I've done both. Our rhubarb patch has not suffered one iota from either procedure.

Q: I’m so glad I found your Web site. I hope you can help me. Not knowing that a common lilac bush sends out hundreds of suckers, I planted two blueberry bushes about 5 feet in front of the lilac bush. Now there are too many lilac suckers for me to yank out every month. It’s back breaking! After reading other posts, can I spray a broadleaf herbicide on the lilac suckers around the base of the blueberry bushes or would that hurt the blueberry bushes and poison the berries? Four years ago, I inserted a plastic wall into the soil. I was hoping to prevent the suckers from going toward the bushes. It didn’t work because the suckers went below it. My next option is to kill the lilac bush, but I’ve heard that wouldn’t stop the suckers! I’m desperate to save my blueberries and hope you can help. (e-mail reference)

A: You've made it clear that you want to save the blueberries, so the lilac has to go. Get a chainsaw and cut it out while it is still in leaf and has just finished blooming. This will help minimize future sucker growth. When they do come up, spot spray them with Roundup to kill them. Any material that hits the soil is immediately deactivated and will not harm the blueberries.

Q: I have a white birch tree in my backyard that I transplanted there. It was doing well until last year, when it started losing its leaves. The tree did not produce any leaves this year. It looks dead. I have a couple of other birch trees that are growing, but some of the branches do not have leaves. I am concerned that these trees will follow the path of the one that looks dead. The soil in my backyard is a foot or so deep, with clay under that. I am wondering if that is my problem. Perhaps there is not enough good soil there for trees to prosper. (e-mail reference)

A: Borers immediately come to mind. However, it takes a few years for the borers to kill a tree. I would suggest trying to locate a tree expert who is competent in diagnosing plant problems. The expert can determine what caused this mature tree to decline so quickly. It is important to get that determination made so the other trees can be saved.

Q: I would like to plant a row of trees that will produce a privacy screen. I'd also like something that will be effective in the winter. I was thinking of some sort of arborvitae, but I'm not sure what kind would be best for my soil conditions or our winters. I was wondering if you had any suggestions. (Fargo, N.D.)

A: Arborvitae purchased from a local nursery or garden center is what you want. It will have the right species for our winters and soil conditions. There are several to choose from, but I hesitate to make any suggestions in case the nursery or garden center happens to be sold out of that particular one. Just don't plant them too deeply and don't overwater.

Q: I planted cannas lilies on the south side of my house last year. The plants get full sunshine. They did great! After they were touched by frost last fall, I cut them down a lot and let them overwinter like that. However, I still haven't seen them sprout this year. Are they slow to return due to our cooler weather? Did I kill them? Thanks for your advice! (e-mail reference)

A: Don't be so quick to accept the blame. Everyone who does exactly what you did will have some kind of attrition during the long winter. They probably dried to the point of it being lethal. Generally, they are removed from storage about a month or two before being repotted and watered to get some size on them prior to summer's arrival.

Q: I rescued four cactus plants a week ago. I’m pretty sure they are San Pedro cactus plants. I noticed that they have dry spots on some parts. What should I do? I also want to repot them, but in a single pot. Would that harm them? (e-mail reference)

A: The dry spots probably are some corky tissue that has developed in response to some injury, such as insects, weather or previous handling. The repotting in a single container should not be a problem, but be sure they are not overcrowded.

Q: We have a ring in our boulevard grass that grows darker and taller than the surrounding lawn. From my Web research, the ring appears to be what is known as a fairy ring, although we haven't noticed any mushrooms in the area. We wonder if this is likely to be the cause of it or if there are other problems. Also, is there anything we can do to get rid of it? (Fargo, N.D.)

A: That is indeed a fairy ring that you are describing. It shows up where there were older trees on the site at one time or construction debris left at the site. Another cause is excessive thatch. To control the problem, there are some basic maintenance practices you can perform. Core aerate the area. While you are at it, aerate your entire lawn, but do that area last. That will keep the fairy ring from spreading to other parts of your yard. Fertilize with a typical lawn fertilizer and keep it watered. The area might become hydrophobic (water repelling). If that happens, use a wetting agent to get the water to penetrate to the root system. There are at least three fairy ring fungi, but only one produces visible mushrooms as far as I know. The others simply show the darker color ring. Eventually, every lawn outgrows this fungus.

Q: Three years ago I received a bartzella yellow peony from my daughter in Green Bay. I get a lot of healthy foliage, but no blooms. What can I do to make it bloom? The people at the nursery where she bought it told her it might take a year or so to adjust to being planted, so I assumed that I would see blooms this year. (e-mail reference)

A: The lack of blooming peonies usually can be traced to a few causes. It could be planted too deeply or planted in too much shade. Some people apply too much fertilizer, which causes excessive vegetative growth at the expense of flower production.

Q: I live in a high, cold mountain valley in Utah. The elevation is about 5,500 feet. As near as I can figure, we're about a zone 4. A few times each winter, the temperature will fall to 25 degrees at night. I have a healthy sungold apricot, but the companion moongold apricot that was supposed to pollinate it died seven or eight years ago. The sungold gets lots of blossoms and tiny, pea-sized fruits, but the fruits shrivel and drop off. Two or three years ago, we got a few apricots after we took some blossom cuttings from a distant neighbor’s tree and hung them in my tree. The neighbor’s tree has since died and there are no other apricot trees in the area that I know of. I recently planted a Tilton apricot. Would it work as a pollinator? The information I found says it blooms in April, but my sungold bloomed this year about the first week of May until early June (a little later than most years because we had a late spring). (Herber Valley, Utah)

A: Sorry, I do not have more information! Sungold and moongold are the only two that supposedly can pollinate each other.

Q: I have one violet left after three plants died. I have repotted the remaining plant and placed it under a grow light for fear it wasn't getting enough sun. However, a whitish mold has formed on top of the soil. I am not sure what to do or what is causing the mold. Please help. (e-mail reference)

A: This mold is a saprophyte feeding on the dead organic matter in the soil. Scrape it off the top if it bothers you or appears to be smothering the plant. Generally, this dies out on its own in a few days or weeks. Try backing off on the watering somewhat.

Q: I have been pruning my two arborvitae bushes for 20 years. They always looked great. However, I overpruned the top and side of the bushes two years ago. They both have a bald spot now. Some regrowth occurred last summer, but there is no sign of more regrowth. Is there a fertilizer or something I can use to promote regrowth? I would hate to have to replace them. Thank you! (e-mail reference)

A: It almost never develops regrowth where all the foliage has been removed. You can wait a few more years to see if yours are an exception or just go ahead and replace them now.

Q: Your column is a very nice arrangement that people can ask questions that are a little specific and get a reliable answer. We are inexperienced gardeners, but we planted some bulbs, flowers, tomatoes and green peppers in a very little plot. Was it OK to plant canna, iris, morning glories and a heavenly bamboo bush with our veggies? Are any of these harmful to the tomatoes and peppers we hope to be eating? Thank you for your time and help in advance, (e-mail reference)

A: You have nothing to worry about, so enjoy!

Q: I have two maple trees that are growing small branches out of the bottom of the tree. Can I cut these branches off? Are they suckers? Also, my ash tree has small branches coming up right next to the tree. They have their own root system. Can I cut those off? I really enjoy your Web site because it is very informative and you always answer my questions in a reasonable time frame. (e-mail reference)

A: Go ahead and cut the branches off. After that, spray the cut ends with Sucker Stopper RTU. That will keep them in check for the rest of the season. Simply pruning them back is like cutting hair because regrowth will occur in a matter of weeks in both cases.

Q: I don't know if you can help, but I have a burr oak that has done well. However, this year, all of the new growth has small, brownish/gray fleshy balls that are slightly oblong. If you smash them, the inside has the consistency of the inside of a blackberry. It is stunting the growth and many shoots are breaking off the tree. I don't know if it is an insect or something else. I have sprayed with insecticides, but without success. I didn't see this condition noted in any of your questions under oak trees. Let me know if you can help. (e-mail reference)

A: These are galls that are formed when the buds are just beginning to open. It is caused by the stinging and egg-laying of a very small wasp. They usually do not damage the plant and often disappear in subsequent years. Spraying is possible, but the timing has to be perfect. It also may be unwarranted in many cases. I suggest snipping off as many as you can and disposing of them. You should be free of the problem in a few years. They are not lethal to the plant, but are decorative (or annoying) to look at.

Q: I have a question about a tree disease. I have a row of old chokecherry trees in my yard. Two years ago, I noticed that early in the summer, some of the leaves on one chokecherry tree started to turn brown on the outer edges. The browning progressed until the entire leaf was brown and it also caused the edge of the leaves to start to curl as they turned brown. The leaves usually would remain on the tree, but they would all be brown and curled. This usually happened in June. By early July, the leaves were all brown. The next year, many of the branches on that tree would show significant dieback and more and more branches would not produce leaves as time went on. One whole tree was affected one year. The next year, the tree appeared dead and did not leaf out at all. That tree ended up being removed. I am not sure what type of disease this is, but it has appeared in the middle of the row. I am seeing a few branches on some other nearby trees displaying similar symptoms this year. I have pruned out many of the affected branches to hopefully slow or stop the spread of whatever is causing this problem. Many young sucker chokecherry seedlings around the affected trees show symptoms also. Some of the leaves on the affected trees also have raised, yellow/green bumps on the leaves. This could be related or could be a secondary insect problem. I have attached some photos of some of the branches I pruned off. Hopefully that will help you identify the disease. (e-mail reference)

A: It looks like a combination of X-disease and some kind of gall-forming insect damage. Kasia Kinzer, NDSU's plant diagnostician, is getting a copy of your e-mail. Perhaps she can make a more positive identification from the photos. She also may request that you send her a sample or two so that a complete analysis can be carried out.

Q: I hope you can help us. We bought a home with young Norway spruce trees planted in a row in the backyard. We need to put up a fence for various reasons. The fence will need to be placed about 4 or 5 feet in front of the trees. The trees are too small to touch the fence right now, but I am concerned about what will happen in the future. I cannot change the position of the fence. Should I move the trees or will the trees adapt to having a fence on one side? Will I need to trim them in the future? Thank you for your help. (e-mail reference)

A: Put the fence up. When the spruce branches begin impacting the fence in a few years, cut them back to the main trunk. Problem solved and the spruce will be better for it.

Q: Hope you don’t mind the fact that I’m writing you from Michigan. I saw your Web site and it sounds like you are a big fan of Chinese elms like I am. My problem is I ordered a Chinese elm online about three years ago. However, I am suspicious it may be a Siberian elm. While the tree is young, how can I tell the difference? It is too young to exfoliate bark or to bear seeds. If it is a Siberian elm, I would like to get rid of it before it gets too large. (e-mail reference)

A: You can tell the difference easily. Chinese elms have a very slender stem and very small buds. Siberian elms have large, bulbous buds. The leaves are similar in description. However, the leaf base on the Chinese elm is unevenly rounded. The petiole is at least one-quarter inch long or longer. The buds are the big clue to zero in on. You probably have a Chinese elm because a Siberian elm would have had twig die-back by now. Glad to have another fan of this beautiful tree. Perhaps someday our climate in North Dakota will get mild enough for us to grow some here.

Q: We have two white lace cap hydrangea bushes that never have bloomed. They get some late-morning sun and some early afternoon sun. They seem to require a lot of water, which I forget to do a lot of times. Do I need to fertilize them? If so, when do I fertilize? (Williamsburg, Va.)

A: If you’ve had them for years in this location and they aren’t very tall, then you might be in a zone where the winter temperatures kill the flower buds. This species of hydrangea flowers on last season's growth. Lace cap hydrangeas fall into the category of being fussy to care for. They need watering on a regular basis. Also, a monthly application of Miracle-Gro fertilizer would help them get into more growth and possible flowering.

Q: Through the years, I have tried to establish an asparagus patch. I plant roots that are a year old. They come up fine the first year, but most do not come back the second year. I decided to try again this year. All 11 roots have emerged and are looking good. What can I do to help them come back next year? I have fertilized using a granular phosphorous blend. Do I cover them this fall with straw to protect the roots? (e-mail reference)

A: Allow the fern growth to remain so it can trap snow. It easily should be hardy to your part of the state. About the only thing I can think of that would kill it off is poor drainage. Generally, your area of the state is not plagued with poor-draining soil. With the price of asparagus these days, one could finance a college education with a half-acre of this vegetable!


NDSU Agriculture Communication

Source:Ron Smith, (701) 231-8161, ronald.smith@ndsu.edu
Editor:Rich Mattern, (701) 231-6136, richard.mattern@ndsu.edu
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