How can I rid my greenhouse tomatoes and peppers of spider mites?


I have a small greenhouse and had spider mites on my tomatoes and peppers last year, both in individual pots and in the permanent bed. Should I empty the soil from the pots and bed, assuring that there will be no spider mites this year or will they not winter over? 


Jonathan Foster, Community Education Assistant

I’m sorry to hear about the spider mite issues–they can be quite a pain (I know from experience, though mine have mostly been houseplants).

Spider mites can definitely overwinter in the soil, depending on which species you’re dealing with. Because your greenhouse is a manageable size, I would advise at the very least replacing the soil in your containers, and giving the containers a good, thorough washing. If it’s a manageable task, you could also replace the top few inches of your in-ground bed, especially since you had them there last season. There are some methods of biological and organic control (read up more on spider mites in this bulletin from the Virginia Cooperative Extension, courtesy of the State of Maine’s website), as well as some best practices advice for how to avoid conditions conducive to spider mites, but chemical controls are difficult and can be ineffective. At your scale, a good washing of everything and some new soil may bring you quicker, better results. With spider mites, preventing them from getting started works better than treating them once they arrive.