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Hortiscope: Roundup won't kill tree roots growing in sewer lines


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?

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?

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.

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?

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.

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