Best Practices for Preventing Damping-Off and Other Fungal Diseases

Illustration of damping off Pythium sp. affecting tomato seedlings, by Margaret Senior

Damping off is a fungal disease that can cause germinating seeds to rot (called pre-emergence damping off) and young seedlings to shrivel and die (called post-emergence damping off). My first experience with damping off was textbook: I was growing cantaloupes from seeds, and one day, the seedlings looked pinched at the base, where the soil touched the growing stems. As happens with post-emergence damping off, the seedlings had begun to rot from the roots. Within a few hours, the stems of the infected seedlings turned brown, and the seedlings later collapsed on themselves. As is often the case, none of them were salvageable once the problem became apparent. 

Happily, damping off is preventable if you follow these best practices:
 

1. Start your seeds off in sterilized seed-starting mixes, not potting soil or dirt from your yard.

2. Don't get your seedlings soggy-wet. Make sure that whatever pot you're using has good drainage, and let the planting medium get fairly dry between waterings.

3. Make sure there's good air circulation in the room you're growing your seedlings in. You can ensure this by setting up a fan, just like a small-scale version of what commercial greenhouses do, which will provide the added benefit of helping your seedlings grow strong stems as they push back against the gentle air flow you've provided.

4. Don't sow your seeds too close together. You want air to circulate between your seedlings. 

5. Give your seedlings adequate light, preferably in the form of some grow lights. (I just use fluorescent grow lights that I bought at the local hardware store.)