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Hortiscope

Ron Smith answers questions about flowers, trees, gardens and shrubs.

By Ron Smith, Horticulturist

NDSU Extension Service

Q: We have three old plum trees (delicious plums) that seem healthy but are growing more and more little shoots from the root system. To mow the lawn, I have to cut back these shoots. We transported these trees from a previous residence and never had this issue. (e-mail reference)

A: Trees often do this when they are under some kind of stress from borers, cankers, root problems or soil compaction causing anaerobic conditions. There isn't much you can do about it that would be practical. There is a product on the market that is called Sucker Stopper RTU that is sprayed on the sucker after it is cut off. It will inhibit that particular sucker from developing again for the rest of the growing season. If there is a sucker or two or if they are confined to being just around the base below the graft union, this action is practical and easy. If there are dozens scattered throughout the lawn area, it becomes more impractical and difficult to control. I used to have plums in my yard, but gave them up because of their repetitive suckering. Somewhere along the line, your fruit-bearing (scion) wood is losing vigor, so the rootstock is taking over. It will be a slow and progressive process. Eventually, you will have to give up the fight and take the trees down. If you choose this removal option, consider doing it after the trees have leafed out and produced fruit. That way, there will be less energy left in the roots to send up that would produce a forest of sucker growth.

Q: I've been searching on the Internet for a solution to the problem I'm having with my mint plants. One thing that caught my eye was your answer on identifying a plant someone had that was described as being skunky. I think that is a good way to describe mine. My mint plants used to smell great. In the past year or more, all of mint plants, including any new plants from rooted cuttings, have developed this rank, rubber smell when I crush the leaves. They are still minty, but you can tell there is some other smell in there. I've been afraid to use the mint. Some of the plants are in Miracle-Gro Organic Choice soil, some have extra perlite and some are in other types of organic soil. All are outside on a north balcony. I recently started giving them water from my reverse osmosis drinking water system, thinking the chlorines or chloramines were doing something. If you have any ideas on what is happening or can point me in a better direction, I'd appreciate it. (e-mail reference)

A: I have never heard of mint going "skunky." What I am afraid of is that you really don't have mint plants. They could be look-alikes, such as penny royal, which have poisonous oil that can cause liver damage. I wouldn’t use anything that doesn't smell like 100 percent mint. If someone can come up with a better answer as to why mint may smell this way, I'd certainly welcome your input.

Q: I planted around 100 bulbs last fall that were beautiful this spring. I let all the foliage die, and now it's September and my house has sold. I would love to take them with me but am moving into an apartment this fall. Can I pull them up, dry them out and keep them in a cool place for storage? The bulbs would be in storage for more than a year. (e-mail reference)

A: You are better off just forgetting about these bulbs, but know that the new owners of your property will be delighted to see how beautifully they will show next spring. To attempt to bridge the time gap between now and next fall is close to impossible for a backyard gardener to accomplish. Chilling them sufficiently now would be a possibility in the north, but keeping them from growing next spring would be almost impossible. It isn't something I would attempt to do because I think the result would be a lot of frustration and nothing to show for your effort. Perhaps you could make a deal with the new owners to enjoy the flowering bulbs this spring, but you would dig them up at this time next year.

Q: I live next to a dike. When the dike was raised last spring, the city used junk dirt (lots of rocks and glass pieces). It was seeded by the city along with one side of our yard that was damaged during the flood of 2009. Consequently, our side yard has become a weed field. We have been busy pulling them and throwing them away, but the dike continues to sprout tons of weeds. When is the best time to lay grass seed this fall? What blend? We have some morning sun and lots of dappled shade in the afternoon. Someone told me to put down a pre-emergent first thing in the spring. Won't doing that stop the grass seed from sprouting? I know you're the expert who can help me. (e-mail reference)

A: At this late date, you need to get the existing weeds under control with a postemergent, such as Trimec Plus, that will take care of the most obnoxious weeds. Next spring, as the forsythia is blooming, get a pre-emergence herbicide down that contains Siduron (Tupersan) as the active ingredient. It will allow the cool-season grasses, such as Kentucky bluegrass or creeping red fescue, to germinate while keeping the annual grassy weeds, such as crabgrass, foxtail and barnyard grass, in check. For the seed mix, look for something labeled for shady lawns. It will be high in creeping red fescue cultivars that are adapted to shaded locations.

Q: This year, I grew some white pumpkins, but I don’t know when they will be ready to be picked. (e-mail reference)

A: Pick them when they have colored completely. Being nonclimacteric fruits, they will not ripen any further once harvested. If in doubt, wait at least until a light frost kills the foliage.

Q: I planted a vegetable garden this year for the first time. I planted some asparagus crowns in June. They all have come up and have stalks with feathery fingers. What do I need to do to prepare them for winter? Do they need to be trimmed back? If so, how much do I trim? Do they need to be mulched or fertilized? Also, there are some volunteer asparagus plants in and around my garden. Can these be transplanted now to be placed with my new plants? Also, one of these plants has small red berries on it. Is that asparagus or an imitation of sorts? A second question has to do with some mature lilacs on this property. I did not get them trimmed back this spring after blooming took place. Is it too late to trim them now or should I just wait until after next spring's bloom? Thank you for your help and your interesting column. (e-mail reference)

A: Allow the asparagus ferns to remain for the winter. The ferns will trap snow, which will act as an insulator against severe low temperatures and be a source of moisture next spring. Remove the fern growth when the snow is gone and before new spears appear. With transplanting, do that next spring while they are dormant. The plants you see with the red berries are the female plants making seed. As for your second question, pruning your lilacs this late in the year is not recommended due to the probability of the plants not healing before winter closes in. Pruning after next season's flowering is a better alternative.

Q: I would like to know when to prune my three crape myrtles. I have cut them back once in 10 years, so they have become very tall with long limbs. My grass is now shaded too much. The blooms have started to fall, but some are still present. Can I cut them back now or do I need to wait? (e-mail reference)

A: The first thing you should know about crape myrtles is that they are different from most trees and shrubs because they bloom on what's called new wood or new growth. Other trees have flowers coming from the growth that was made the previous year. Therefore, anything that you can do to make the crape myrtle grow once it leafs out in the spring will result in more flowers this coming year. Crape myrtles thrive on water and fertilizer. If you fertilize on a regular basis, you will have more flowers than you know what to do with. However, don't use lawn fertilizers. Lawn fertilizers have nitrogen content that is too high, which will result in weak, leggy growth. Look for a flowering shrub or rose fertilizer. Despite the common practice of heavily topping crape myrtles, the plants will look and perform better with just light pruning. Since pruning encourages new growth, pruning in late summer or early fall will result in tender shoots just in time to be nipped by cold weather. In other words, at this time in September is not a good time. If you prune too late in the spring, you will remove the flowering stems and the plant won’t bloom. That’s why late winter or early spring is the ideal time to prune crape myrtles because they will produce vigorous shoots at just the right time. For routine, light pruning, remove the branches that are crossing or rubbing, as well as any dead, spindly or broken branches. Older crape myrtles produce an abundance of suckers, which also should be removed.

Q: I have two hibiscus acetosella plants in pots that I plan to keep through the winter. They have not bloomed, but I do enjoy the foliage. They are rather spindly, so I’m wondering if I can I cut them back. If so, how far back? Should I fertilize the plants after bringing them inside? I plan to have them under a grow light. Other years, I've planted them in the ground, where they grew huge, and then just left them outside to die. (e-mail reference)

A: You can cut them back to 4- to 6-inch stubs. No fertilization is needed until new growth after the pruning takes place. Even though you will provide adequate light energy for growth using grow lights, keep in mind that it will not be anywhere near equal to what the plant would receive on a typical summer day, so only use half the amount of fertilizer that is recommended.

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 ronald.smith@ndsu.edu.


NDSU Agriculture Communication

Source:Ron Smith, (701) 231-7123, ronald.smith@ndsu.edu
Editor:Rich Mattern, (701) 231-6136, richard.mattern@ndsu.edu
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