By Melanie Mathieson
The Gardening Guru
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 you must be concerned with when starting seedlings in the house or greenhouse, and directly in the garden, called damping-off—and it quickly can 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 wipe out your seedlings very quickly, it also can set your indoor gardening schedule back by weeks.
This column will give you a better understanding of damping-off, and how it occurs, so you can proceed confidently to get those seedlings started successfully in the house, greenhouse, or directly in the garden—and keep your crops right on schedule.
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 usually is damping-off that has destroyed your seedlings, not poor germination.
The other type of damping-off is post-emergence. This form 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 seedling, 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 certainly is 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.
Never eat treated seed, or use it as food for birds or animals, as it is very poisonous.
You can make your own treated seed by mixing powdered benomyl fungicide or Captan (a pinch of powder in each seed packet and shaken well to mix) with the seed just before planting.
Using treated seed is most important when sowing directly into the garden early in the growing season, but can be used indoors, as well.
With the unpredictability of early spring weather, and a good chance the soil will stay wet for extended periods of time, treated seed will help to reduce the development of fungi on your seed and seedlings.
You can make your own liquid fungicide by using benomyl fungicide (one-half tablespoon per gallon of warm water) or a liquid product called No-Damp™ (mixed with water according to directions) to water the potting mix right after the seeds have been planted.
If you see mould or any first signs of damping-off appearing, you may have to repeat the treatment by watering with the fungicide solution again, following the directions carefully.
Just like the tips I give for preventing moulds and fungal infections in your outdoor plants, good housekeeping comes into play here, too.
First of all, make sure all of your pots, planting trays, and containers are clean and sanitized if being reused by cleaning with a bleach solution (one-quarter cup of bleach per one gallon of warm water).
When pre-wetting peat pellets or peat pots, use the water solution with fungicide as mentioned above.
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 weak seedling, making it 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).
And make sure the seedlings are evenly-spaced and are not overcrowded to ensure good circulation.
If you have to thin small seedlings, trim the seedling you wish to remove right at soil level with scissors. This prevents over-plucking and disturbing the soil around the other seedlings.
Now that you understand what damping-off is and how it can be prevented, you certainly can proceed with confidence and get those seedlings started.
I even may have solved the mysteries of some of your past crop failures.
Now you won’t have to let damping-off put a damper on your gardening experience.