Soil never goes bad just inactive. Recycle it forever and ever. Recharge it with some compost and soil amendments; keep it hydrated and it will be good to go for another cycle. Your soil actually gets better every time you do this. Add in worm castings, lime, and maybe some kelp meal (among many other inputs if desired) and let it set for a month to normalize the PH. You can also add in any plant trimmings or leaves from harvesting; cannabis plant material breaks down fast in active soil and contains everything a cannabis plant needs. Usually adding a lot of organic matter drops the ph slightly; letting it sit for awhile allows microbes in the compost to do their thing. Some call this "cooking" the soil.