Persistent Deadly Mildew
Answered by: Inge Poot
Question from: Margaret Kapounek
Posted on: April 15, 2004

I have a problem that I’ve been struggling with for about 3 years. I began growing herbs indoors, annuals and perennials, some of which would be transplanted outdoors in the spring and the rest would remain in the house. The first year was fantastic. The herbs were beautiful and I encountered no problems with them. The second year however, I began noticing white mildew on the peat pots, the soil and the plants themselves. In time green mold also began to grow. I tried many cures but none worked. The plants all died. I had 120 herbs and many houseplants at the time. I had never previously encountered this problem in all the years that I’ve grown plants. I have many books about plants and checked everything I might have been doing wrong -- over watering, insufficient light source, overcrowding the pots, etc. I threw out all the plants and the peat pots they were in. I scrubbed everything that I would have used for the plants and disinfected everything with bleach. I began again. This time I chose terracotta pots and carefully watched the plants. Within about two weeks, the white mildew was again covering everything and the plants began to die. I made one more attempt, throwing everything out that might have been contaminated and this time using only plastic pots that I sterilized. Sure enough the mildew and mold returned. I gave up trying to grow indoor herbs. I cannot figure out what is causing this unless the mold and mildew have spores that are dormant until I start growing plants. If this is the case, what can I do about it? Im really frustrated with this because I recently purchased seeds from your catalogue but I’m afraid to try them because I don’t want them to die off like the others.

This fungus must like your conditions really well to be so successful. You will have to change your growing conditions to foil the fungus. The other problem is going to be to find the reservoir of spores. Did you scrub the windows? The condensation encourages all sorts of mold to grow. Floors and even the walls could hold millions of spores that gradually move around on air currents and settle on the plants, etc. You also have not mentioned air movement. Get a fan and have it blow over, not on the plants, to keep the plants dry so that spores can neither settle nor find the moisture required to germinate. Keep the pots on the dry side. Boil your water before using it on the plants -- just in case it is the reservoir of spores. Also, be sure to sterilize the soil before use - do not believe the label on the bag from the store -- it has sat around the store long enough to be anything but sterile. To sterilize the soil (actually there is no such thing as sterilized soil, it is just sort of pasturized, with the most virulent fungi killed off, but it does not get anywhere near all the resting spores), let it dry out and then rehydrate it with boiling water. Sow as soon as the soil has cooled. Experiment with a baking soda and soap spray -- it will make the soil alkaline and may not be good for all plants, but the fungus may not like it either. Since you do not have the problem out of doors, use some of the soil from your garden to start the seeds. Garden soil usually has many competing micro-organisms in it that keep each other in check. If you can sow direct in the garden without damp-off, then that soil should be fine for indoors too -- try some without sterilizing even -- in another room, so that if it fails it does not saturate your growing area with spores.

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