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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: When we moved into our home six years ago, there was a beautiful plum tree in the yard. It didn’t produce fruit, but it did have lovely blossoms in the spring. After the tree started to decline, we were told that it had developed pests and was dying, so we had it removed. Is it OK to plant another plum tree in that same location? I seem to remember that the original person who diagnosed it said it was best not to plant the same tree there because the other tree did not do well in that spot. Is this true? The tree trimmer said plum trees don’t live very long and suggested planting a birch tree. We already have one but it looks skimpy compared with the plum tree. There also is a very large and shady sycamore tree nearby, so maybe the lack of sun will be an issue for any new tree. (e-mail reference)

A: Since you mention a sycamore tree in your note, I know that you are not writing from North Dakota. The person who removed the plum tree is correct that it is not a good idea to replant the same species in the same location, especially when the previous tree was diseased. It also is true that plum trees don’t live that long. Decent-looking plum trees after 25 years are becoming more of an exception rather than the rule. A birch tree should do OK unless the large sycamore is densely shading the new planting. I would suggest considering a flowering dogwood planting if they grow in your region. However, if you can grow sycamores, you should be able to grow flowering dogwoods. The only stopper there would be the soil being too high in pH alkalinity or too brutal of an exposure to the elements. Generally, flowering dogwoods do well as a subcanopy tree, so the shade from the sycamore shouldn't be an issue.

Q: I received a Christmas cactus more than a year ago. At that time, it had three leaves. Since then, it has grown two more leaves and has a couple more just starting to grow. How big does the plant have to be before it begins to bloom? I understand that I need to give it a rest period to encourage blooming. I just found your website and am thoroughly enjoying the information you provide. Keep up the good work! (e-mail reference)

A: As far as size goes for blooming, I don't know that there is any size determination to consider. Small plants will give you few blooms, while large plants should have many blooms. Try giving the plant a little stress by reducing the watering and temperature a little. Start giving the cactus 13 to 14 hours of total darkness every day to see if that sets up some flower buds. If you've read my responses to Christmas cactus questions, you've likely seen the ones where people don't do any fussing over the plant but it blooms profusely. Others follow a strict schedule but don’t get any results. Our former department chair got his Christmas cactus plants to bloom even though all he did was give the plants water. Be patient with the plant and observe how it responds to what you do. I don't think you'll be disappointed

Q: I grew a sweet potato vine in a large pot this summer. When I took the vine out of the pot, there were two tubers in the dirt. Are the tubers edible? (e-mail reference)

A: They are edible. If they taste good is something you'll have to decide. Brussels sprouts also are supposed to be edible, but to me they aren’t!

Q: I live on Maui and have a mock orange hedge that is covered with whiteflies. I doused the hedge with detergent spray, so the flies are gone. However, now all the leaves are dropping. They are falling off even though the leaves are green and healthy looking. (e-mail reference)

A: As long as the plant's cambium wasn’t burned from the detergent, it should recover unless you really doused it enough to poison the soil, which I doubt. So hang in there and be a little patient. Depending on the growing cycles where you live, the plant should be back in full leaf eventually.

Q: I've had a wonderful curly spider plant for a couple of years. It produces tons of babies and is extremely healthy. However, I thought the new growth would curl, but it doesn’t look like it will. Any idea why the new growth won’t curl? In addition, this new growth is solid green, not variegated like the old growth. (e-mail reference)

A: You have discovered a chimera! This periclinal or sectoral chimera is reverting to the original character of the plant. Without boring you with too many details, chimeras are the result of cell mutation at or near the apical meristem of the plant. This mutation may be spontaneous or induced by irradiation or treatment with chemical mutagens. If the cell that mutates is near the crest of the apical dome, then all the other cells that are produced by division from it also will be mutated. The result will be cells of different genotypes growing adjacent to each other in the plant’s tissue, which is the definition of a chimera. The variegation of plant leaf tissue is one of the most common horticultural forms of chimeras. You're witnessing it in your spider plant. It also occurs in other plants, such as the variegated snake plant, thornless blackberry and many African violet cultivars. Doing something to prevent this from continuing would require you to follow where the green leaves are originating from on the crown of the plant the next time you repot. You then would need to cut away that part of the crown and leave just the part that is producing the admired chimera.

Q: I would like to start a bunch of new walnut trees in pots because it is easier to keep the seeds in pots until they are bigger and then transplant them. Can I keep the walnut seeds through the winter and plant them next spring? How do I store the seeds through the winter to prevent them from freezing? (e-mail reference)

A: Black walnut seeds need to be subjected to freezing temperatures. I'd suggest getting them in containers and set them outdoors where they can get snow cover. Any viable seeds should break dormancy next spring and grow nicely. Their first season of growth is phenomenal! Enjoy.

Q: Are poinsettia plants poisonous to children or pets? (e-mail reference)

A: They are not poisonous to the extent of killing a child or pet. However, because it is a euphorbia species, some people are sensitive to the milky sap the plant produces. Some folks classify it as poisonous because of that sensitivity, while others don't. Either way, it is not a good idea to ingest it. I'm told that the taste is repugnant enough that one couldn't eat much of it anyway.

Q: Do you have a suggestion on how to get rid of what looks like white mold on the red blooms of my poinsettia plant? (e-mail reference)

A: The white mold likely is cottony cushion scale. It would be very unusual to have white mold on a poinsettia grown as a houseplant because the air inside during the winter usually is too dry to have it develop. Dip a cotton swab in rubbing alcohol and rub it over the spots you are calling white mold. If I am incorrect and you do have a low-grade fungus, it probably is powdery mildew. In either case, you are better off dumping the plant than trying to correct the problem.

Q: I received several amaryllis plants four years ago. They all bloomed the first year, but only four bloomed the next year. Last year, two plants bloomed and only one this year. I cut off the bloom stem each time they bloomed. I set them on the back porch when the danger of frost is gone. They sit in an area that does not get direct sun. I stop watering them in August when the foliage dies. I put them in a cool basement for about three months. Why do I get nice green foliage and no blooms? (e-mail reference)

A: You are doing better than average at getting these bulbs to bloom! Go to to read my information on amaryllis plants. I have had mixed luck with getting them to rebloom, so I gave up after a couple of years. Get another plant because it saves a lot of aggravation.

Q: I got a cyclamen plant about a week ago. It started losing flowers, and the leaves are turning yellow. I wrote to a place that has experts on cyclamen. I was told that I was overwatering the plant, so I stopped watering it as often. I also was told that if it gets too wet, the roots would rot. I read on another website that my problem is not watering enough, so I began giving it a little more water. So far, there hasn’t been any improvement. Does the plant need more or less water? Have the roots rotted? I’d really appreciate any information about cyclamen care you could give me. I got the plant for a special occasion and it means a lot to me. (e-mail reference)

A: The wilting can be caused by too little or too much water. In the latter case, it is caused by anaerobic conditions existing from saturated soil and possibly rotting or rotted roots unable to take up water. Cyclamen plants are very fussy. They should not be watered from above. Water by immersing the pot in tepid water and then allowing the excess to drain. On the other hand, the plant should not be allowed to dry completely. Keep the plant in bright, indirect light and try to keep it in a location where the temperature stays around 60 degrees.

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

NDSU Agriculture Communication – Dec. 28, 2010

Source:Ron Smith, (701) 231-7123,
Editor:Rich Mattern, (701) 231-6136,
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