The Q&A Archives: Window Box Flowers

Question: I have a window box (in a sunny area in San Francisco) and I seem to keep losing whatever is planted there to a disease of some sort. It takes over the leaves with a matte whitish substance, like a mold or fungus? Any ideas?

Answer: Based on your description, I'd say the plants developed powdery mildew. This fungal disease occurs when plants are grown under conditions where humidity is high and days are warm but nights are cool. Some plants are more susceptible than others to powdery mildew. Try increasing the air circulation around the planter and providing plenty of room between plants. While not totally immune, these plants seem to resist powdery mildew: lobelia, dianthus, celosia, marigold, nasturtium, petunia, scabiosa and statice.

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