Most people toss old potting soil and buy new bags every time they replant—but you really don’t need to. Nature never replaces soil; it recycles it. When a plant finishes its life cycle, the old roots become food for microbes and the next generation of plants. Your pots and raised beds can work the same way. Soil is a bank: if you don’t make deposits, it eventually runs out.
When you’re ready to reuse soil, remove the old plant itself, but you can leave the root system in place. You can break the soil up if you want to, but you don’t have to—especially in raised beds. Those leftover roots become organic matter the biology will break down.
Add worm castings (no more than about 20% of your total volume) to bring biology back into the mix. Then add your favorite organic amendments—alfalfa meal for nitrogen, kelp meal for potassium and trace minerals, and fish bone meal for phosphorus. Moisten the soil, cover it with a lid or tarp, and let it sit for 2–4 weeks. This resting period lets microbes wake up, digest the old roots, and stabilize the nutrients.
After that, you’ve got refreshed, living soil—ready to plant again without buying more.