Answer: Two groups of mites account for most of the plant-damaging species of mites. The tetranychid family includes the webspinning spider mites, the red mites and the broun mites. The eriophyid family include the rust, bud, and blister mites. One other mite family, the tarsonemids, contains the cyclamen mite which is a serious pest of strawberries.
If Spider mites are feeding on deciduous plants, females will overwinter under the bark or in the soil after the leaves fall. This is also true of brown mites, which live in organic litter and on decaying twigs, and of the cyclamen mite which overwinters in the crowns of plants.
So, it's possible that there were mites in your potting soil by virtue of the fact that it's mostly organic matter. It's also possible that mites began their journey into the root area of your plants by invading the crowns of the plants and moving down into the soil when there was nothing else for them to consume.
You might take another soil sample to the Extension Office and ask them to send it along to the Puyallup Plant Clinic for soil specialist Craig Cogger to take a look at.
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