The Q&A Archives: Controlling Fungus on Onion

Question: Onion plants die off when I start them in the greenhouse 8-10 weeks before putting them outside. For some reason I have had trouble the past 3 years (but no problems before then). I use soilless material to start them. Could it be a fungus? Lee Aegidius

Answer: It sounds like you're having trouble with "damping off". This is a fungal disease that attacks and kills seedling plants. Conditions that favor damping off are: Crowding of seedlings, high humidity, and lack of sufficient aeration. So keep seedlings thinned, and be sure to provide adequate ventilation. And try to keep the growing area relatively cool. Since the fungus enters the plant at the soil line, you can try this method: once the seeds are planted, but before they germinate, cover the soil with a fine layer of "play sand" -- this is sand that has been sterilized (you should be able to find it at a hardware store or lumberyard). This provides a sterile, dry -- and therefore unfavorable to the fungus -- surface at the point it usuallyenters the stem.

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