When starting seeds indoors you do not have to worry about the weather, insects or the myriad of plant diseases and fungi that can affect your outdoor vegetables, trees or flowers, but there is one disease that you must be concerned with when starting seedlings in the house or greenhouse and directly in the garden, called damping-off. Damping-off can quickly turn the initial joy of seeing your young seedlings poke through the soil and start to grow into a complete crop failure almost overnight. Not only can damping-off can wipe out your seedlings very quickly but can also set your indoor gardening schedule back by weeks.
Damping-off can be caused by any one of the many types of soil fungus. There are two types of damping-off and both types can occur in young crops indoors or outdoors. Pre-emergence damping-off occurs when the sprouted seeds rot in the soil, shortly after they germinate. The seedling never emerges from the soil and the gardener doesn’t know what happened and just chocks it up to poor seed quality. If you have purchased or collected high quality seed, it is usually damping-off that has destroyed your seedlings, not poor germination. The other type of damping-off is post-emergence damping-off. This form of damping-off occurs either as the seedlings emerge, or shortly after they emerge from the soil and show signs of wilt or a rot-infested spot on the stem. The seedling then wilts, collapses and quickly dies because the fungus has girdled the stem with infection, preventing the seedlings from being able to draw the required nutrients and water it needs to grow. Damping-off can affect almost any seedlings but is most common with lettuce varieties, spinach, beans and other vine plants (cucumber, squash, etc.) cabbage, eggplant, peppers, tomatoes, onions, corn, beets, carrots and flowers like petunias and snapdragons.
No matter what you are planting indoors, I always emphasize that you must use a high quality sterilized soil or soil-less mix. Taking this point to heart is certainly one of the best ways to prevent damping-off. Another method of preventing damping-off is to use seed that has been treated with a fungicide. If the seed has been treated it will be indicated on the seed package and the seed will have a coloured coating on it.
Just like the tips I give for preventing moulds and fungal infections in your outdoor plants, good housekeeping comes into play here as well. First of all, ensure all of your pots, planting trays and containers are clean and sanitized if being reused, by using last week’s tip of cleaning with a bleach solution (1/4 cup of bleach per 1 gallon of warm water). Once ready to plant, use only plump, healthy and crack-free seed. Do not over water or fertilize the seedlings excessively, especially when they are first emerging from the seed and soil. Do not let the potting mix dry out but do not let the soil remain soggy. Adding water to the bottom of the tray or with a fine sprinkling of watering can help you control the amount of water added. Also, don’t let the condensation get too thick on the clear cover of the planting tray or container. If you see mould or an over abundance of condensation developing, remove the cover and wipe dry before replacing. Make sure seedlings receive adequate light, good air circulation and are never overcrowded. Seedlings that receive too much heat or light can grow quickly and become leggy, while not enough light makes a pale and week seedling, making the seedling more susceptible to damping-off. Good air circulation can help keep the climate of the house more favourable for the seedlings by regulating the temperature and allowing for the evaporation of excess moisture. You can improve air circulation by using a fan on low near the seedlings, just don’t put the fan so close that you create a strong wind for fragile seedlings. Make sure the seedlings are evenly spaced and are not over-crowded to ensure good circulation.
Now that you understand what damping-off is and how it can be prevented you can certainly proceed with confidence and get those seedlings started and you won’t have to let damping-off put a damper on your gardening experience.