Damping-Off. What is it? How to avoid it.
The most common disease of seedlings started indoors is called damping-off. Damping-off is a general term for diseases that attack seedlings in the early stages of their development. It causes the seedlings to collapse or, in some cases, can even cause the seed to die before emergence. Several fungi cause damping off. The methods of prevention are the same for all of them. By practicing the following guidelines, damping-off is seldom a problem and you will produce nice, healthy seedlings.
1. Any containers used for seed starting should be thoroughly washed with soap and water. Then wipe the surfaces with a solution of water containing about 10% bleach.
2. Use a sterile seed-starting mix. We like Jiffy Mix, but you can also use a mix of fine-grade vermiculite and milled sphagnum moss.
3. Don't crowd seeds when sowing. If seedlings are crowded, remove some of them so each plant has good air circulation.
4. Avoid overwatering. Use only containers with drainage holes and don't leave the containers standing in water for any length of time. Allow the surface of the seed starting mix to dry a little between waterings. Remove plastic covers from seed trays after germination to lower humidity levels around seedlings.
5. When transplanting seedlings, handle them only by the leaves and not the stem. Injured stems are more susceptible to damping-off.
6. Grow seedlings in a well-ventilated, brightly lit area. Weak, leggy seedlings will result if plants are grown in poor light at very warm temperatures. Seedlings grown in bright light at cooler temperatures will be stocky and healthy.
7. Visually, infected seedlings will show constriction and discoloration of the plant stem at the soil line. Should you see any infected seedlings, discard them immediately to avoid spreading of the infection. If you want to try to save the remainder of the plants in the flat, make sure to move the flat to another location in an open area away from other seedlings. Don't try to transplant as you'll just transfer the disease to the new soil. If you wish to reuse the flat, be sure to wash and disinfect it thoroughly.