The Q&A Archives: Dubious Dreadful Dying Dieffenbachia

Question: I have a Dieffenbachia in my office which is not doing well. It sits in a sunny East window on the 7th floor of the buiding which is shaded by another building for about 4 hours mdday. For the first 9 months it's been VERY healthy and growing like crazy. About 8 weeks ago I noticed some problems: yellowing leaves, pale new growth and loss of lower leaves. I recently (6 weeks ago) replanted it in a 10 inch pot using Peter's all purpose house plant soil. I was very careful to only slightly loosten the roots, and did not densely pack the new soil. But, this hasn't stopped the problem. My concern then became that I was over-watering. Two weeks ago I cut down on the watering from every 5 to 7 days to 10 to 12 days. But, I am still getting the same symptoms. The roots don't seem particularly soft nor is the plant leaning over at all. I have fly strips out and have caught numerous gnat-like flys. Any suggestions would be greatly appreciated.

Answer: The gnats are probably fungus gnats, which in small numbers are not harmful, only annoying. The symptoms you describe could be due to a watering problem. These plants can usually withstand some drying, so I have a feeling the problem is overwatering. This is exacerbated by the fact that you've repotted--there's even more soil to hold excess water. If the plant gets at least some direct sun each day, and isn't in a very dark spot the rest of the time, it should be OK--but pale new growth is often a sign of lack of light, so if there's a brighter spot, I'd move it there for now. Remember, the less light the plant gets, the less water it needs. Also, air conditioning reduces the need for water if the temp. is set low. Check the soil before watering. Allow it to get dry down to an inch or so, then water thoroughly, and wait until the top inch is dry again. This will also help control the gnats.

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