How to Prevent Damping Off

Did all of your seedlings start to wither and die? Or did your seeds never germinate? It might be that damping off is to blame.

Starting seeds yourself is a great way to save money, and when you start your own seeds, you usually have a greater number of plant varieties to choose from. Starting seeds indoors is usually fairly straightforward and simple, but the dreaded damping off diseases can derail your gardening efforts.

What is Damping Off, Anyway?

“Damping off” is a term that refers to several soilborne fungal diseases that affect seeds and young seedlings. It usually affects seeds started indoors, but it can also affect plants growing outdoors in cold, wet soil.

Sometimes the seeds never germinate, and rot in the ground. More often, though, the seedlings emerge and begin to grow vigorously. They appear healthy. Overnight, they might develop withered or pinched stems. The stems might fall over and the plant rapidly dies. You’ve just lost six to eight weeks of work in a few days time. Once damping off begins in a seed tray, it’s hard to stop. It’s likely that most, if not all, of the seedlings in your seed tray will eventually succumb to the disease. Hence, prevention is the best strategy for combating this frustrating problem.

Immaculate Conditions

The first step in preventing damping off is by starting with sterile conditions. Use a light, soil-less potting mix made with perlite or vermiculite. Don’t use regular garden soil, which is too heavy and often contains pathogens. Sterilize the potting mix by placing it in roasting bags or pans and baking it in an oven set at 200 degrees for 20 to 30 minutes.

You can microwave potting mix to sterilize it instead, if you prefer. Mix 1 cup water with 1 quart potting mix. Place the mixture in a microwave-safe bowl. Place a lid loosely over the bowl and heat on high for eight minutes. Remove the bowl from the microwave and secure the lid tightly. Let it steam an additional 12 minutes or so. Cooking potting soil in the oven or microwave does create an earthy odor, but it quickly fades.

Next, sterilize your tools and other equipment. If you’re reusing seed trays, wash them in soapy water to which you’ve added 2 tablespoons of chlorine bleach. Rinse and dry carefully.

Moist, Not Soggy

Seeds need moist soil to germinate, but it should never be wet or soggy. Mist the soil with water in a spray bottle every day or so, just so the soil feels slightly moist to the touch. Damping off is much more prevalent in wet conditions. Some gardeners water from the bottom of the trays instead, which also seems to minimize fungal diseases. Fill a sink or pan with water and place the tray in it. Leave the seed tray in place for about 15 minutes, or until the top soil feels slightly moist.

If you cover your seed trays with plastic wrap or a plastic dome, punch a few holes in these materials so air can circulate freely. Remove them as soon as the seedlings germinate. Avoid overplanting and thin seedlings out when they stand 2 inches tall. Good air circulation is essential to keeping plants healthy at any stage of development.

Make sure young seedlings have adequate light. In most cases, you’ll need a grow light or some other type of supplemental lighting. A heating pad under the tray can hasten germination, which also reduces problems. Remove and discard any trays as soon as you see symptoms of damping off so the disease doesn’t spread to other trays. Always wash your hands with soap and water after handling the plants or before moving onto another tray, since the disease can be passed on your hands.

Antifungal Measures

Commercial growers often use a commercial fungicide to combat damping off disease, but this measure is rarely necessary at home. Instead, try spraying young seedlings and the soil with a mixture of 1 tablespoon hydrogen peroxide with 1 quart of water. Cinnamon dusted on the soil after planting also acts as a natural fungicide, as does powdered charcoal.

Learn more information on keeping seedlings healthy.

Visit the following links:

Seedling Damp Off from the University of Vermont

Starting Seeds Indoors from Purdue University

Learn more about cinnamon and damping off at YouTube.

Julie Christensen learned about gardening on her grandfather’s farm and mother’s vegetable garden in southern Idaho. Today, she lives and gardens on the high plains of Colorado. When she’s not digging in the dirt, Julie writes about food, education, parenting and gardening.