The Q&A Archives: Mold With Starting Seeds

Question: I tried to start tomato seeds on a propagation mat this year and the soil got some mold on the top. How can I prevent this? I had the trays covered and as moist as I normally do when starting other seeds. Do I need less moisture or should I not cover the trays when using a heating mat?

Answer: Usually, mold is a sign that the soil is too moist and that temperatures are either too hot or too cold. The soil should be barely damp, the pot covered with plastic wrap, and the soil temperature ideally between about 75 and 80 degrees. Be alert and remove the cover as soon as the seeds germinate, also be careful to start with scrupulously clean equipment and fresh sterile potting mix. I hope this helps.

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