Watermelon Damping Off Info – What Makes Watermelon Seedlings Die

By: Liz Baessler

Damping off is a problem that can affect many different species of plants. Specifically affecting seedlings, it causes the stem near the base of the plant to become weak and withered. The plant usually topples over and dies because of this. Damping off can be a particular problem with watermelons that are planted under certain conditions. Keep reading to learn more about what makes watermelon seedlings die and how to prevent damping off in watermelon plants.

Help, My Watermelon Seedlings are Dying

Watermelon damping off has a set of recognizable symptoms. It affects young seedlings, which wilt and often fall over. The lower part of the stem becomes waterlogged and girdled near the soil line. If pulled out the ground, the plant’s roots will be discolored and stunted.

These problems can be directly traced to Pythium, a family of fungi that lives in the soil. There are several species of Pythium that can lead to damping off in watermelon plants. They tend to strike in cool, moist environments.

How to Prevent Watermelon Damping Off

Since the Pythium fungus thrives in the cold and the wet, it can often be prevented by keeping seedlings warm and on the dry side. It tends to be a real problem with watermelon seeds that are sown directly in the ground. Instead, start seeds in pots that can be kept warm and dry. Don’t plant the seedlings out until they have at least one set of true leaves.

Often this is enough to prevent damping off, but Pythium has been known to strike in warm soils as well. If your seedlings are already showing signs, remove the plants that are affected. Apply fungicides containing mefenoxam and azoxystrobin to the soil. Be sure to read the instructions – only a certain amount of mefenoxam can be safely applied to plants each year. This should kill the fungus and give the remaining seedlings a chance to thrive.

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Some quick tips for making sure your seedlings flourish!

  • Once your seedlings have 2-3 sets of leaves, the most important thing to do at this point is to supplement them with nutrients! Most seed starting mixes have very little nutrition if any at all. We suggest using ¼ to ½ strength liquid fish/seaweed fertilizer every other watering for your seedlings to be at their happiest!
  • Using a soilless seed starting mix to start seeds is very important. Soilless seed starting mix is light, fluffy, and perfect for your seedlings to grow strong, sturdy roots! Garden soil or potting soil is often far too heavy and lacking in drainage, making it hard on the delicate root systems of the young seedlings.

What are your favorite tips and tricks for seed starting?

17 Responses


I had those little gnats this year. It’s bad news if you have them! They lay eggs and the larva are in the soil and eat the roots. I had 6 inch plants that should have had a large root system hardly had anything. I tried treating the soil and plants (above the soil) with non toxic dish soap suds, and even watering the plants with the soapy water, then flushing out the soap after 15 minutes or so. It seemed to really take care of the problem.

Chris Hunt-Lex.,NC

My seeds did great and are already producing, won’t be long before we have to freeze and can, thanks for the article….


This was helpful in that I believe I need to fertilize, going by the suggestions. I see the person writing this has been gardening for 20 years. That’s commendable! I have been gardening for 45 years—-still learning! I used to be able to start my seeds in my growing medium and not worry, not any more. The new mediums out there just don’t have the nutrients my old one did. At least that’s how it seems to me. Thanks for the article. It was helpful.

Sara Clay

At first sign of damping off, water from top with chamomile even if they don’t need water, drain well and do not rewater til soil is on the dry side. Has worked for me to save most of the damping off seedlings!

I start all my seeds in pure compost from my piles, screened through 1/4” hardware cloth, with a sprinkle of bone meal mixed in. If snow melt here in Vermont is late and even raised beds are too wet to work, they get weekly fish emulsion to keep them vigorously growing, or even potting up for those that like warm soil. So I take care not to start seed too early since younger vigorous transplants do better than older root-bound ones.

No need to buy that expensive sterile nutrient-less starting mix that dries out so fast if you have compost that stays so nicely moist and is forgiving if neglected for a day or three. I bring in several 5 gallon buckets full each fall and store in cool cellar with an old dinner plate on top so it has a bit of air around the edges and stays damp but not moldy. The worms (and no doubt the beneficial bacteria and fungi) are still living when I start my seeds in spring. I put the worms in kitchen compost and dump them into the outdoor pile.

Only had damping off 2 years out of almost 30 here, and the chamomile tea did the trick for most of the seedlings.

Linda Paulson

Potting soil also causes little flying bugs similar to fruit flys

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