Seedlings are often attacked by a variety of fungi known as "damping-off" diseases. To prevent that from happening, here are some steps you can take:
- Purchase disease free seeds from a reputable dealer. Some seeds come with fungicidal coatings on them which will be direct sown out doors in cold soils, such as corn and peas. Seed borne disease can also be avoided by soaking the seeds for 15 minutes in a bleach soak (one teaspoon per quart of water) prior to sowing.
- Sterilize your pots or trays in a water/bleach solution (10:1 ratio).
- Use sterile well drained soil mediums.
- If you sow your seeds indoors in a germination room like I do, mist seedlings in communal pots or flats once or twice per day with water containing an anti-fungal agent such as Captan (what I use). You can also use chamomile tea, or clove tea. A fungicide misting is especially important if you're sowing seeds in a damp or humid basement.
- Provide constant air movement 24 hours per day, but not directly aimed at the plants. I use a table top fan that's not tied in with the light timer's outlet. This helps the seedlings to aspirate, and excess soil moisture to wick. If you do everything else right but do not provide plenty of air movement, you can still get damping-off.
Hope this is helpful.