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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: Can you tell me why my tomatoes crack? I water regularly and fertilize with tomato spikes. Otherwise, the plants look healthy. We had the same problem last year, so we changed the variety, but it didn’t help. I would appreciate if you could help me. (email reference)

A: Cracking on the stem end of the tomato is due to a surge of water coming in faster than the skin can stretch to absorb it to relieve internal pressure. As long as you are not growing tomatoes for showing off, the edibility and flavor of the fruit are not affected. While this can happen to any tomato variety, select those that are known to be more resistant to cracking. Select those tomato varieties that have elastic skin such as daybreak, early girl, Earl of Edgecombe, Heinz 1350, jet star, Juliet, mountain delight, mountain pride and valley girl. Also try to maintain a consistent watering schedule, and mulch the plants two to three weeks after planting to help maintain consistent soil moisture.

Q: How often should I be watering my silver maples? They are about 3 years old. Will too much watering cause their root systems to be too shallow? (email reference)

A: After being in a planting site for that many years, a silver maple should have a well-developed root system. In spite of that fact, it is still a good idea to provide water to the roots when no significant rainfall occurs for more than two weeks of extended drought and heat. Always water at and beyond the drip line to encourage the roots to follow the migrating water. If your soil is deep and well-drained, the roots will follow the percolating water through the soil profile. If the soil doesn’t drain well, the roots will tend to stay closer to the surface.

Q: I transplanted a few wild roses last year. Last fall, they seemed to go dormant early. This year, the roses came out with healthy-looking leaves but no blossoms. The leaves disappeared and then new, healthy-looking leaves emerged. Those leaves also are gone now. It looks like someone stripped them from the branches. Any ideas? (Crosby, Minn.)

A: There could be a number of reasons why your wild roses are behaving this way. Beetles can strip plants clean of foliage or a drought/flood cycle could do the same thing. The best thing going for you is that they are wild roses. Wild roses have a deep genetic well of survival resources. All I can tell you is to monitor the roses to see if you can detect anything going on that could be causing this flip-flopping behavior.

Q: If it is oak galls the residents at Red Willow Resort are dealing with, would their yard be covered with leaves and stems from their oak trees? One resident has picked up many garbage bags of leaves and small branches that have snapped off. (email reference)

A: Petiole galls would not cause that kind of destruction. The problem could be caused by squirrels, twig girdlers (beetles) or a combination of the two. Prior to chewing the limb off, the female beetle will make slits in the stem and lay eggs. The wind eventually blows these branches out of the tree and spreads the eggs around the area. The eggs hatch in the fall, and the small larvae burrow into the branch and lay dormant during the winter. In the spring, the beetle larvae will feed and develop rapidly in a tunnel inside the branch. Late in the summer, the adult beetles emerge and the cycle starts over. Chemical control is not effective or recommended. Collect the loose branches and burn them or place them in the trash to reduce the population for next year. While the damage can seem unsightly, very little damage actually is done to the tree. If this isn’t it, then I would need a detailed photo or two of what is going on.

Q: I was reading your Hortiscope from quite a few years ago where you mentioned that Siberian elms were hard to kill. Is there a chemical that can be sprayed to kill them? I had a producer ask me about what he could spray to kill a Chinese elm in his pasture. If you could help me out, I would greatly appreciate it. (email reference)

A: Siberian elms can be wiped out with any good vegetation killer. Ortho and Bonide come to mind. The problem is that the effect might be compromised when used this late in the season. I’m not familiar with the product labels but, if you checked, the labels would have the details that you could relate back to your client. My comments from years ago were in reference to the many maladies these trees get hit with, such as herbicide drift or migration. These trees get hit with an encyclopedia of diseases and a battalion of plant-destroying insects but they somehow survive!

Q: If you could, please tell me what is wrong with my impatiens garden. It is in a rather sunny spot, properly irrigated, and there is no evidence of wilt. However, they quit blooming. Could the problem be powdery mildew? (Minnesota)

A: It is impossible for me to determine what the problem is with your impatiens. I encourage you to contact the plant disease clinic at the University of Minnesota by going to The website will have instructions on where to send a properly prepared sample.

Q: My tomatoes are just starting to ripen. As they ripen, they are rotting on the blossom end. At this time in the growing season, is there anything that can be done to save the tomatoes? (email reference)

A: Cut off the rotted end and eat the rest of the tomato in a salad, salsa or soup. Future ripenings should be free of blossom-end rot. Try to keep the water supplied to the plants on a regular basis.

Q: I have a tiny cutting from a small-leaf linden that I believe has rooted. I have had it covered in plastic for five to six weeks. I am wondering if I should plant my tiny tree in the ground this fall or keep it indoors. I live in northeastern Ohio. Thank you for any advice. (email reference)

A: Plant it. Being a temperate-zone tree, it needs to go through the seasons to survive. I'd suggest setting it outdoors now if you haven't done so. Place the tree where it will get a northern or eastern exposure so it gets conditioned to the outdoor environment and goes through the seasonal changes. Be sure to protect it from rodents before the snow flies.

Q: I have several quaking aspens and Russian sages. Both are good at suckering. I can clip or pull them and get along with that. However, the aspen suckers are starting to show up in my neighbor’s yard. Is there a product I can use to stop the suckering? Do I apply it directly on the sucker? Can I spray the suckers with weed killer or will that harm the mature tree? (email reference)

A: There is a product called “Sucker Stopper RTU” that you should be able to get at any good garden supply outlet. You also can find it on the Web at It isn’t cheap but it works. Using a weed killer may end up causing harm to the tree.

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 email For answers to general horticultural questions, go to

NDSU Agriculture Communication – Aug. 29, 2012

Source:Ron Smith, (701) 231-7971,
Editor:Rich Mattern, (701) 231-6136,
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