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Hortiscope: 55-year-old dieffenbachia needs a fan to move the air

Q: I have dieffenbachia plants that are very healthy. However, I can't keep them growing upright. They start to get top-heavy and then bend and curl. The parts that grow from the stumps after making a cutting seem the most susceptible. My place only gets sun from one direction. I should add that these plants are descendants of a plant my uncle bought for my aunt 55 years ago.

A: Research three to four decades ago found that houseplants that were not subjected to forced movement from a breeze or other mechanical means grew fast but were weak and spindly. The majestic plants that one sees indoors are getting movement from fans that build "stress cells." I would suggest that you take a cutting again, but this time put a circulating fan in operation for about 12 hours a day as it grows. Supplement it with extra light if necessary.

Q: I have had spider plants for decades. In the last 18 months, something strange has been happening to the plants. One by one, the lower leaves are rotting from the inside. This goes on until the plant dies. The roots seem fine.

While the leaves are browning, there is new growth and the rest of the plant seems fine. It started with one plant and gradually spread from room to room. At the moment, only the bathroom plant seems OK. I tried baby plantlets, but the same thing happened. I will be extremely grateful for any light you can shed on this problem.

A: This sounds like the soil or media has some kind of fungal pathogen in it. Are you using sterilized or pasteurized media in growing these plants? I would suggest repotting any surviving plants in new or well-cleaned containers. Use a soil media that is known to be pasteurized or sterilized. Be sure to cut off anything that appears to be dead or decaying.

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