Orthene is biodegradable. BobZ is right and it would work very well for both aphids and mites. No fuss no mess and your stress level will reduce significantly. Just because there are those who prefer to avoid chemicals doesn't mean there is no place for them. Merit might be more readily available by you and you might want to try that in lieu of orthene. Maybe your neighbors have a little they might be willing to share with you. Anyway, if you use orthene or Merit... I don't believe you would need to worry about nuking the medium. Both should take care of the aphids as well as the nymphs and it should last long enough to kill any eggs in the soil.
"To eliminate the aphids you will need to, at least partly, understand their life cycle. In the early spring the first aphids appear from eggs laid in your soil the previous fall and these climb up your plants and start to produce live nymphs. Since the total life cycle of an aphid is about 25 days you can see they don't have time to do much more than eat and produce. People have sprayed them off their plants and found more the next day and decided that the ones they sprayed off had returned, not true. Those are the nymphs maturing and taking the place of the ones washed off and since you can easily have 5 generations on your plants with many more coming you can begin to see the problem."
It was my understanding aphids will feed on roots. Some aphids also bore through stems.
http://www.hort.wisc.edu/masterg....ids.htm
Interesting tidbit for anyone who has ants out and about who ends up with an infestation of aphids this coming summer on their outside plants-
"Ants will protect aphids from predators, move them from plant to plant when necessary and even protect them in the ants’ nest in many cases over winter. This mutualism has been observed since ancient times and is well-documented by many research scientists. In addition, ants will feed on plant nectars produced at nectaries in flowers and interfloral nectaries."
John Warner, PhD qualified entomologist
University of Florida
Fort Lauderdale Research and Education Center, Ant Lab
I saw a special on ants and aphids once on tv and I was spellbound. Didn't hurt that the photography was so wonderfully entrancing either.