Outside grow with spider mites ?? Now thats weird. 'Never seen a mite problem outdoors as natural predators eliminate them. If you've rotting vegetation around or near your plants, get rid of it, as well as anything else that might encourage these evil bastards. Indoors, despite what queenster says, mites are virtually impossible to get rid of, even using no-pest strips. You can control them by lowering temps. to 20 deg. c. or so and letting the humidity drift to 70% or so, enough so that you can get a decent harvest. I've had the problem myself many times. After the harvest I fumigate the growroom with burning sulphur. Kills bloody everything !
What exactly is your situation outdoors ? Are your plants in a patch with other vegetation close by ? Can bugs and birds and other wildlife have free access ? Spider mites outdoors are a new one on me. In fact I'm sure somebody told me once that ants chew them up, and you should see plenty of ants around farming the aphids that appear for their sweet dew.