If you start your own seeds, it is only a matter of time before you become familiar with damping-off, that indiscriminate killer of seedlings. The disease is caused by several species of fungi, and can infect young plants of all varieties, whether they are grown indoors or out.
Damping-off fungi can be transported in soil and on gardening tools. They thrive in cold, wet conditions.
- White fuzz growing on soil.
- Seeds rotting before germination.
- Stunted growth.
- Sudden wilting.
- Stems rotting at soil line.
- Seedling death.
Unfortunately, seedlings that already display symptoms of damping-off have a low survival rate. While careful nursing may be able to prolong their lives, destroying them is best to avoid the spread of disease. Throw away the soil that the affected seedlings were growing in, and sterilize the containers if you intend to reuse them.
Once damping-off has appeared in your seedling trays, all seedlings are at risk of the disease. To save the survivors, move them to a warmer room, and point a small fan at them to provide air flow. Make sure the surface of the soil dries out between waterings. Some gardeners have used seaweed extract and neem oil, pressed from the seeds and fruits of an Indian evergreen, with success.
Preventing damping-off starts with good plant hygiene:
- Disinfect seedling trays and containers after use.
- Store seedling trays and containers in a dry area to discourage fungal growth.
- Fill seedling containers with quality seed-starting mix, not garden soil.
- Practice crop rotation in your garden.
The next step is to avoid the buildup of excess soil moisture:
- Make sure seedlings are grown in a room with good airflow.
- Sprinkle sand, peat moss, or the mineral vermiculite on the surface of the soil.
- Let the surface of the soil dry out between waterings.
- Water the garden in the morning so that the surface of the soil is dry by nighttime.
- Sprinkle cinnamon on the surface of the soil to absorb moisture if you accidentally overwater.
Finally, take a few extra precautions:
- Use a soil thermometer to make sure that the temperature is ideal for the specific seed that you are planting.
- Plant seeds at the depth and spacing recommended on the packet.
- Wait to apply fertilizer until the seedlings are established, as excess nitrogen can increase a plant’s susceptibility to fungal infections.
“Soil Temperature Conditions for Vegetable Seed Germination”
Useful factsheet listing minimum, maximum, and optimum soil temperatures for starting common vegetables.