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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: In 2009, I planted some apple trees. I was told to paint the trunks so they wouldn't burn in the sun. I painted them with an oil-based enamel paint. Now I heard that I should have used a water- based paint. Have I killed my trees? (e-mail reference)

A: I don't think so, but the next few weeks will tell. Keep your fingers crossed.

Q: Our water has iron in it. Will this affect my houseplants? I seem to be able to grow ivy with no problem. I have a Christmas cactus that grows very slowly. I recently purchased some kalanchoe plants from a local grocery store. I was told that I could plant them in my flowerbeds in the spring. Is this true? My soil is sandy. The area I want to plant them in does not get a lot of sun. The tips of my other plants do turn yellow. Is this because of the water? If I boil my water, will it make a difference? (Toronto, Ontario)

A: Water that is classed as being high in iron also many times has a high total soluble salt content. Christmas cactus is a plant that lives under tree canopies in the Brazilian jungle, so it gets distilled water (rainwater) for sustenance. Your water that is high in iron content could be causing slow growth and yellowing of the foliage. Boiling the water will not make a difference because it will not take out the iron and other salts. If you want to invest in something, get a filter that can be attached to your faucet that will take out most of the salts and other contaminants in your water. What is good for you to drink also is good for your plants! The kalanchoe plants can be planted outdoors when the danger of frost is past. They need to be brought back in before the frosty weather arrives again in the fall.

Q: We received some tulips in a pot as a gift. After the tulips bloomed and faded, I put the entire pot in a dark closet with all the foliage on them to let them die down completely. Now what do I do? I would like to replant them toward the end of the year, but I don't know what to do with them in the meantime. (Venice Beach, Calif.)

A: You might have made a mistake. If the tulips were placed in the closet before the foliage had a chance to fade naturally in the sun, the bulbs probably are dead or close to it. What you should have done is allowed the flowers to fade and cut back the flower stalks but continued to water the bulbs as long as the foliage remained green. When they started to fade to yellow and you could pull the leaves off with a simple tug, the bulbs were dormant for the season. If you placed the bulbs in a refrigerator for about 60 to 90 days to allow for a sufficient chilling period to set the flower buds, you could bring them out into normal air temperatures and they would send up new growth and flowers. What you have done to these plants is kept them from manufacturing food to replenish what was used up for this season's growth. I suggest dumping them.

Q: I have a box elder tree that is in the wrong place at the wrong time! The tree is next to the house and sewer lines. It has gotten too big and has to be removed. I would like to leave most of the trunk for the decorative effects but stop the roots from going any further. Can I use Roundup for this and how should it be applied? (e-mail reference)

A: Roundup would be difficult to use on a tree this size, so Roundup wouldn't work to your satisfaction. I would suggest making contact with an International Society of Arboriculture certified arborist to see if the tree can be injected with something more effective that will kill the tree completely and quickly.

Q: I enjoy reading your seemingly infinite insights on trees. I have come to realize how much people care for their black walnut trees. I also am fond of the two I have in my backyard. However, I would love to have one that doesn't produce nuts. I'm talking huge crops every year! Has anyone ever figured out how to sterilize a black walnut tree? (Buffalo, Minn.)

A: Not to my knowledge! The tree contains male and female flowers. I think this makes it rather difficult to come up with a way to eliminate the messy nuts that these trees are large producers of. If the flowers were perfect (hermaphroditic), with both sexes present in one flower, such as an apple tree, then fruit reduction or elimination would be a good possibility.

Q: I have a question about a red maple tree. Last spring, I decided to get rubber mulch pads to put around the base of the tree. Within a few days, the majority of the leaves fell off the tree. I assume the ground got too hot. I decided to discard the mulch pads as a result. It took several months for the tree to produce more leaves. Shortly after, we had some cold spells and freezing temperatures, so all the leaves fell off again. Now it is late March and the tree hasn't produced any buds yet. Several people have the same tree and all have begun to bloom. The tips of the branches appear to be red, so I am sure it is still alive. What can I do to get the tree to produce leaves? (Jacksonville, Fla.)

A: Be patient. If the tree has any energy left, it will leaf out. From what you told me, the tree had its carbohydrate production cut down with the two defoliations. When the leaves drop prematurely, the amount of photosynthates that they produced are limited. If it happens twice in a season, it is akin to someone pushing a drowning person under water for the third time, which might be the death push! There is reason to be optimistic because the buds are red. Fertilizing will not help and don’t overwater. Maintain the tree as you normally would. If it is going to break dormancy, it should do so in a month or less.

Q: I've just moved into a house that has three jade plants growing in a sunny garden. Two plants were flowering when we moved in, but now the blooms have faded. Should I deadhead the clusters of brown, crispy flowers? Should I pinch them off or use garden shears? Is now a good time to fertilize the plants? (Los Angeles, Calif.)

A: I would suggest using sharp pinking shears to nip off the spent flowers. When the plants start to exhibit new growth, you can give them a little fertilizer. Use a liquid or granular fertilizer that you will lightly spread under the canopy of the plants.

Q: Last summer, I bought two Rocky Mountain hibiscus plants that were great. They bloomed once, but I’m wondering if there is some way to make them bloom more often. I live in an apartment. I hope to place them outside, but I am not sure when to do that. What temperatures do they need? During the winter, I let them die back and cut them way back. I actually thought they were dead, so I am glad I didn't throw them out! They came back with long stems, but I would like them to be more compact. They still are light green and starting to droop. I think this is because the stems cannot hold the leaves up. I have no idea what to do. They also have leaves turning yellow and dropping off. Some of them are burned on the edges. I water them when I remember. I don't think I over or underwater them. I think it would help if I moved them outside. (Colorado)

A: The problems you are having are indicative of the plants not getting enough light. You should have placed them outside after they finished blooming last summer to let them go into natural dormancy. Prior to winter's arrival, you should have plunged the plants, pot and all, into the ground in an inconspicuous spot on the property. The plants would have been able to respond to normal weather conditions and you would not be having the problem you are now experiencing. I would encourage you to get the plants outdoors in gradual increments during the next couple of weeks so they begin hardening off. If you place them outside without this process, the plants will be set back or killed due to the sudden shock of a different environment. When you do move the plants outdoors, put them in a protected location away from direct winds or reflective hot afternoon sunshine.

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

Source:Ron Smith, (701) 231-8161,
Editor:Rich Mattern, (701) 231-6136,
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