As you know citrus plants and spider mites go together and are hard to get rid of. There are some factors you can control which will make them less susceptible:
- keep in bright diffuse light not in hot sun
- ensure the soil continues to provide iron and manganese micro nutrients. A citrus fertilizer and regular top dressing or putting fresh soil at the bottom of the pot will help.
They key to controlling spider mites is to understand their life cycle. As Wikipedia notes an egg can go from just laid to ready to lay more eggs in just five days.
This is why the key factor is timing. Whatever control agent you use such as dish soap or neem oil or a pyrethrin based solution you need to get complete coverage and to repeat every 5 days for as long as it takes.
Moving the plant to a shower and giving it a spray with dish soap and water then rinsing off after a few minutes is effective if you persist.
The no holds barred control option is to cut the plant back to remove all leaves and spray with dish soap and water every five days. Citrus will bud out from old wood but it takes a while before they look nice again.
Finally, make sure that there are no other plants that have spider mite in the same room. Adults can spin webs and float around to new plants.
