New plants = new soil.
Trying to save a few dollars by reusing soil is really quite pointless, the build up of fertilizer salts, pathogens and other crap just means your plants are behind the eight ball from day one. Give them the best chance to perform.... this means fresh, clean and healthy soil each time.
Considering the entire cost, time and effort to grow plants, soil is only a minor outlay, skimping here just leads to second rate results.