The Simple Mix That'll Help You Successfully Reuse Old Potting Soil

Whether you have a container garden or other potted plants on the patio, once any of those plants lives out its full life cycle, you're left with a pot full of old potting soil and possibly a twig or three. Even if you buy plants at a garden center, there's sometimes a little potting medium left in the nursery pots after you've transplanted the actual plant into the ground. In either scenario, with a little help, that leftover potting soil may still have some usefulness left in it. Mixing it with an equal amount of new potting soil replaces the nutrients that plants need. It aerates the mixture a bit and also saves money since you'll only have to buy half as much potting mix for your next round of potted plants. To save even more money when you're filling large plant pots, use leftover or broken bricks as plant-pot filler. The added weight also helps prevent pots from getting knocked or blown over.

It's worth noting that not all old potting soil is worth saving. If the previous plants occupying it were diseased or infested with pests, it's best not to reuse that old soil because these same problems could be present within it long after the old plants have died. If you see odd discoloration or mold, which may look white, orange, or even pink atop the old soil, it also shouldn't be reused, as you don't want to spread any issues to your new plants.  

Depending on how much old potting soil you have, either dump it into a plastic tub or atop a tarp; the tarp method could be a good option if you have numerous large containers full of old soil. Spread the soil out a bit, and remove any stems, old plant roots, and debris you find. Break up hard clumps as well, as old potting soil tends to get compacted over time. That old soil also becomes depleted of nutrients as plants use them and as water runs through the pots.

Add in an equal amount of new potting mix, and combine the two soils so they're thoroughly integrated. Mixing the two soils together ensures the soil has some nutritional value for the plants. When it's mixed together, it's also more porous than the old soil, allowing air and moisture to reach plant roots once you set your new plants in pots. It's also why you can reuse old potting soil to improve your garden's clay-heavy soil, making it porous and light enough to allow nutrients and water to reach the plant's roots more effectively. 

If you don't have a new potting mixture but do have some fresh compost, good news: Compost works, too. Just mix your old potting soil with an equal amount of fresh, nutrient-rich compost instead of adding new potting mix. The new soil will have all the nutrients and components needed to help your new plants flourish. You could also reuse old potting soil to help your raised garden beds thrive.