Ron Smith answers questions about flowers, trees, gardens and shrubs.
Q: Is there a proper time to cut down large poplars to reduce the suckering? I have heard that there is a certain time of year that is best. Also, is it better to fight the suckers the year after taking the trees down or treat the stumps to reduce suckering? (email reference)A: Take the poplars down right after the trees have fully leafed out in the spring because their food reserves are at the lowest at that time and would tend to produce fewer suckers. I’d suggest treating the stumps and going after any suckers that will be coming up from the far reaches of the root systems.Q: My Christmas tree is sprouting new needles that are 6 to 7 inches long toward the top and shorter at the bottom. The tree did take a lot of water. I thought it would start some roots but one guy told me that won't happen. I have been told that the tree won’t start roots because it did not go dormant. The grower where I bought it had never heard of this before. What do you think? (email reference)A: The tree apparently had a sufficient cold period to come out of dormancy in your home environment. However, because there was no bacterial formation in the vessels conducting the water, the tree was able to transport water throughout the tree's canopy and get the buds to flush out new growth. It will not form roots, so don't get your hopes up for that. This is not a common occurrence. During my lifetime, I have heard or seen this happen less than a half-dozen times. Enjoy!Q: I have some large silver maples that are in need of pruning because of damage from storms last summer. Many of the branches that need pruning are large. With no leaves on the trees, it is easy to see where the cuts should be made. I have read that maples should be pruned in mid-June. However, because we have so little snow, it would be easy to get at them now. I was wondering if it would do any damage to the trees if I prune them in February or March. (email reference)A: Pruning now will not damage the trees if the pruning is done properly. You will get sap flow from those cuts this spring as the weather warms up, but don't allow that to stress you. The trees will not bleed to death. The sap flow will stop after the trees have leafed out. Callus tissue will begin forming to seal off the cut areas. Do not apply any wound dressings.Q: I've been reading your articles for several years. I enjoy your expertise and answers very much. Do you have any thoughts about the newest U.S. Department of Agriculture plant hardiness zones and the movement northward? (email reference)A: Thank you for being a loyal reader of the articles. Also, thanks for the good question. Yes, I have plenty of thoughts about the new hardiness zones. The new zones are good in many ways. However, a precaution has to be included before we become too complacent about weather extremes. I’ve lived long enough to have a somewhat jaded view of the “everything is easier to grow now.” Avid gardeners are notorious for pushing the envelope of hardiness limitations. I don’t think these gardeners will change their attitude anytime soon. There is nothing wrong with that. I do the same thing and am happy when I can “get away with it.” My friend and colleague Adnan Akyuz, who is North Dakota’s state climatologist, and I have put our heads together on this very subject and are in total agreement as to taking a precautionary approach in pushing the hardiness optimism too far. That’s because minus 25 degree temperatures can show up at any time and kill plants. That is especially true this year because we hardly have any snow cover. Akyuz generated a graph for me that displays the frequency of minus 25 degree days since 1881. I would love it if we could grow peaches in the warmest parts of our state, but I’m afraid they would go the way of apricots. The apricot tree might not produce any fruit for several years, but then produce for a few years followed by the tree getting killed by the cold weather. Sorry for such a long answer. I just wanted you to realize the full impact of what has the potential to take place with the new hardiness zones. The most predictable thing about our weather system is its unpredictability, especially for the long term. Averages are dangerous data to make hard and fast decisions on but that is exactly what the new hardiness zone map reflects.Q: If you could give me advice about my box elder, I would really appreciate it. I live in Pretoria, South Africa. We moved into our home three years ago. There is a wonderful box elder in our yard. However, it seems to be in a bit of turmoil. Some of the branches are breaking off and there seems to be a large area of rot. In the rotted area, the bark is soft and I can tear it off with my hands. I'm not sure how old my tree is. Maybe you can guess from the photos I’m sending. What should I do? I was thinking of cutting off the branches that are having problems. Is this the beginning of the end of the tree? (email reference)A: Thanks for the excellent photos. The problem branches are a significant part of the tree's trunk system. It appears the tree is being killed by a canker disease. A lab analysis is needed to identify the type of canker disease. However, the lab analysis would do little good because the tree is doomed and should be removed professionally before parts of it collapse and cause property damage or personal injury. Sorry for the bad news.Q: A friend of ours has a hibiscus plant that she's had for several years. In the last year or two, she brought another hibiscus plant that she purchased while visiting in Arizona. After a time, some white flies suddenly appeared. She has tried about everything to get rid of the flies. So far, the flies are winning. Do you have any suggestions? (email reference)A: The flies are difficult to get rid of once they start propagating. Get some yellow sticky traps and hang them around the plants. The flies are attracted to the yellow color, so they fly to the trap, get stuck and their lives end there. Traps are about as effective as anything else that I could recommend and traps don’t put poison into the environment. These traps should be available at any major garden center in your area.Q: We have a Cortland apple tree in our backyard. It is starting to drop in apple production. I'm not asking how to fix the tree because it is old and probably has some disease. However, I love the taste of the apples. I have some red delicious seeds, so I am wondering if it is possible to graft a Cortland bud into the red delicious so they taste the same. (email reference)A: A Cortland to red delicious grafting is possible if the red delicious is hardy in your growing area. If it is, go for it.Q: I have been reading through your website to gather some good, basic information. I want to plant a couple of apple trees to provide a large quantity of fruit. I have a limited amount of space, so productivity is important. I prefer really crisp apples that have a tart flavor. Lastly, I am concerned about survivability of the tree through the cold winters here in Baltimore. What species of apple tree would you suggest? (email reference)A: Maryland is a great producer of very tasty apples. There are more than 200 orchards on more than 2,000 acres in your state. I strongly advise you to visit a local nursery or garden center to make your selection and to get professional advice. Empire is a cross between a McIntosh and red delicious. The apples are crisp and excellent for hand eating and in salads. The Fuji is firm and sweet and has red and green stripes. The Rome apples are firm and slightly tart. They are excellent for baking and all cooking purposes. York apples are crisp, firm and tart. They are good for hand eating and all cooking purposes.
By Ron Smith, Horticulturist, NDSU Extension Service