Damping Off - When Seedlings Fail
Copyright © 2011 McGroarty Enterprises Inc.

One of the most heartbreaking moments for any gardener may occur in early spring when their carefully-tended seedlings suddenly keel over and die, seemingly for no apparent reason. This occurs most often in seedlings that have been started early indoors, and the cause is typically one of several soil-borne plant diseases collectively known as damping off.

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The various fungi that cause damping off are all found naturally in soil, and although damping off can also occur in the garden, it is more often a problem in indoor-planted seedlings. The fungi make their way into the indoor germination area by riding along on gardening tools that were used in infected soil, or by planting in infected soil or by planting infected seeds. Some damping off fungi will also reside in plant debris, and it can even survive on gardening gloves that were worn in the previous season's garden.

Damping off symptoms vary slightly depending on the specific fungus that created the problem. It is not necessary to know the names of the various fungi that cause damping off, but it is important to recognize the symptoms they cause. It is also important to understand that once seedling are infected with damping off fungi, they are goners, dead, kaput and they cannot be revived. Therefore, the best way to deal with damping off is to prevent it from infecting your baby plants.

Seedlings that have been infected with damping off will quickly fail. One day they look just fine, and the next day they are withered, fallen over and dead as doornails. Seedlings may discolor or wilt suddenly, their stems may develop dark lesions or become slimy or they become water-soaked, thin and weak near the soil surface, or the roots may rot and blacken. Some damping off fungi cause the seedlings to develop a white or gray mold. Pre-emergence damping off can also cause seeds to rot in the soil just as they begin to germinate.

Losing seedlings to damping off doesn't mean you're a failure at gardening. It's just an indication that you need to refine your seed-starting techniques. It can be very discouraging to lose seedlings to damping off, but this very common problem can be prevented.

A sterile, clean environment for seedlings is the key to preventing damping off. Do not use soil from the garden for starting seeds indoors. Not only is garden soil often infected with fungi that cause damping off, but it is also likely to compact too much for delicate seedlings. Always use a sterile soilless mixture for starting seeds. Coarse sand, milled sphagnum moss or even fine, clean aquarium gravel can be used as a seed-starting medium. Garden centers offer a variety of sterile soilless mixes that are made just for starting seeds.

No matter what medium is used for starting seeds, it should drain well and have a fairly low pH. Mixes with a pH of 6.4 or less are not as susceptible to damping off as those with a higher pH. 

To prevent damping off, tap water should not be used on seedlings. Tap water can be alkaline in many cases and it will gradually increase the pH in the planting medium. Instead, use distilled water. If you know that your water is alkaline, you may also add a tablespoon of white vinegar to a gallon of filtered tap water and use that for watering your seedlings.

The planting medium should be kept moist but should never be soggy. Damping off fungi thrive in conditions that are too wet. Ideally, the medium should be watered from the bottom, rather than the top. To water from the bottom, simply place the flats or pots of seedlings in a shallow container of water until the planting medium has absorbed enough water to moisten it. Do not allow the flats or pots to remain in the water until the medium becomes waterlogged. 

Good air circulation around the seedlings will also help to prevent damping off. Keep a fan running on low speed in the room with the seedlings at all times. The fan should not be blowing directly on the seedlings, it is only necessary to keep the air moving and circulating in the room.

Any gardening tools that are to be used when planting or caring for the seedlings need to be disinfected if they have also been used outdoors in the garden. Tools can be disinfected in a solution made with one part bleach and four parts water, or wipe them down with rubbing alcohol. 

A fungicide may be applied to the seedlings, either as a soil drench if using a liquid fungicide, or a powdered fungicide can be mixed into the planting medium before planting the seeds. Some gardeners have found that damping off can be prevented by sprinkling ordinary powdered cinnamon on the surface of the planting medium, while others swear by the preventative effects of chamomile tea. Hydrogen peroxide has also been used to prevent damping off. Use ordinary 3% hydrogen peroxide, the kind you can buy at a pharmacy or supermarket, mixing one cup with a gallon of distilled water, then mist the seedlings with this mixture.

Once your little seedlings have germinated, emerged and survived any threat of damping off, they should be placed under grow lights or in a bright, sunny window where they can begin to grow big and strong. If the seedlings become spindly or they start to lean toward the light, they are trying their best to tell you that they need more light. If you're using grow lights, move the lights closer to the seedlings. If the seedlings are in a sunny window, they will need to be turned daily to give them adequate light, or they may need supplemental light.