With all the previous worries about mold and trying to sterilize soil we have had in past posts, I just wanted to present my mold killing option. While neem oil can kill mold infections in a few days, prevention is much better. Neem oil can prevent mold too, but you can do one better by killing the source naturally and for free.

I used some badly infected moldy soil to repot my plants. Before I repotted, I took some advice about microwaving soil to steam it by placing the soil in a cheap microwaveable tupperware container with a lid. Add distilled water to the soil and just place the lid on without pressing it down (you don't want the container to blow up) then set it in the microwave for a minute at a time until it is hot to the touch and steamed. This helps to not only kill the mold, but to quickly hydrate the dry moss. Leave the container for a couple of minutes to steam, then pour the soil out on a surface to cool and it is ready to pot up. After that treatment, the soil is completely mold free even after a couple weeks of monitoring. No neem oil or chemicals needed. Just make sure the soil is back to room temperature before repotting the plants. The perlite will turn brownish or yellowish after a couple of days and continue to darken with the pigments in the moss, however; this is only a stain, not mold. That nasty yellow mold will grow up on perlite as a kind of sponge like mass that keeps getting bigger. Stains in the perlite are no worry.