It’s a process that doesn’t guarantee good results, but that doesn’t mean you won’t get them either. It’s a risk because you don’t know exactly how many nutrients are still available in the soil and what you might need to add to balance it. I’d only do it if the previous grow was organic—otherwise, I wouldn’t risk it.
That being said, my Durban Poison actually grew in reused soil, and I didn’t have major issues, just a slight excess of CalMag in the early stage, which forced me to do a flush-style watering to balance the nutrients in the soil.
To reuse my soil, I stored it in a plastic container for a month, watering once a week with molasses to let it cook over time. I added some fresh soil, a bit of SuperSoil, worm humus, mycorrhizae, and leftover solid nutrients from previous grows, like silica, fish meal, blood meal, alfalfa, and dolomite.
That’s also why I took the risk—it was more about using up the leftover nutrients I had at home and avoiding the hassle of carrying old soil from my room to the garden. 🤣