The problem
Repotting often leaves you staring at a pile of old potting mix and wondering: “Should it go in the bin, the garden, or back into another pot?” Reusing soil feels thrifty and sustainable, but tired potting mix can contain compacted roots, harbour pests and be drained of nutrients. So how do you know when to refresh and when to replace?
The hack
Old soil isn’t always bad soil. Most potting mixes lose structure and nutrition over time, but they can often be revived with a bit of care. If the mix smells musty, contains mould or has signs of fungus gnats, it’s best to discard it. But if it’s dry, healthy and crumbly, you can usually bring it back to life.
The method
Tip the used soil into a clean container, break up any clumps, and remove old roots or debris. To refresh it, mix in around one-third new compost, plus a handful of perlite or coco coir, to increase aeration and drainage. For large tropical plants, add a slow-release fertiliser. If you’re unsure about pests, moisten the soil, place it on a tray, cover with foil, and bake it in an oven at 82-93C (180-200F) for 30 minutes to sterilise it.
The test
I used refreshed soil for repotting a pothos. My plant remained happy and sent out new growth within weeks.
The verdict
Refresh when you can, replace when you must. A little maintenance turns old soil from waste into a healthy base for new growth – good for your plants and the planet.
