Why Is There Mold Growing In My Seedling Tray?

When starting seeds indoors, a humidity dome or plastic wrap can help maintain moisture and warmth, two elements that significantly help the germination process along. But what happens if you notice mold growing under the dome after only a few days?

Don’t panic, but the fungus growing on the seed starting mix is trying to tell you something.

The conditions are too wet, and if the situation isn’t controlled, your precious seedlings may eventually face the consequences.

How To Fix It

Increase air circulation to prevent the problem from going any further. Crack open the dome by an inch or two, or poke some holes in the top.

dampening off

If you decide to add a fan to the room, be sure that it’s on a very low setting. Too much air movement can damage brand new seedlings.

Don’t give your seedlings too much to drink; the soil should be damp, never soggy. Remember to always water from the bottom of the tray.

And while the white, fuzzy mold growing on the top of the soil isn’t going to hurt the seeds, it can mess with germination.

Try removing it by gently scratching the surface of the soil with a fork. Be extremely careful doing this if the seeds have already sprouted.

Beware Of Dampening Off

If humidity levels remain too high, fungal growth can cause dampening off, which kills plants at the base of the stem.

Unfortunately, once it starts, there’s nothing you can do to save the seedling. It’s all over but the crying.

dampening off

Avoid this horrid plant disease by practicing good sanitation techniques. Julie Thompson-Adolf, author of Starting and Saving Seeds: Grow The Perfect Vegetables, Fruits, Herbs, And Flowers For Your Garden, recommends the following:

  • Sterilize recycled containers in a solution of one-part bleach to nine parts water.
  • Rinse the containers with water after soaking.
  • Use only fresh seed-starting mix, not garden soil.
  • Offer seedlings plenty of air circulation and don’t water too much!

Remember, once the seeds have sprouted, immediately remove the dome or plastic wrap from the seedling tray.

Happy growing!

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Catherine Sherriffs

Editor at Garden Culture Magazine

Catherine is a Canadian award-winning journalist who worked as a reporter and news anchor in Montreal’s radio and television scene for 10 years. A graduate of Concordia University, she left the hustle and bustle of the business after starting a family. Now, she’s the editor and a writer for Garden Culture Magazine while also enjoying being a mom to her three young kids. Her interests include great food, gardening, fitness, animals, and anything outdoors.