Ask the Expert - Moldy Potting Mix

Daedre McGrath, our Trial Garden Manager, answers questions about using moldy potting mix.

Mold in your potting mix is generally not a reason for concern
Mold in your potting mix is generally not a reason for concern


I just potted a plant using some potting mix I store in a plastic container in my garage. As I was scooping it out, I noticed some mold on the wall of the container. Can I use it, or should I throw it away?
-Charlene P. from Spring Arbor


I would go ahead and use it! We go through hundreds of bags of potting mix each year. Technically the potting mix is supposed to be sterile, but we often find sheets of moss, mold, mycelium, and sometimes large mushrooms inside the bags. We have never had a problem with any kind of disease transferring from the potting mix to our plants. For the potting mix to actually be sterile, it would have to be heated up to kill off any insects, spores, bacteria, etc. The minute you expose the potting mix to air, or have it come in contact with your plant material, it’s no longer sterile anyhow.

Also note that potting mix is not the same thing as soil. Potting mix is usually a soil-free mixture of peat moss and perlite. Sometimes it can contain bark, coconut fiber, sand, or fertilizer granules. If you use actual soil or compost to pot up plants (which I do not recommend), there will definitely be a much higher chance of passing along undesirable pests and diseases.

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