When to refresh or replace used potting mix

Repotting often leaves you with a pile of old potting mix and a choice about whether to throw it away, put it in the garden or reuse it in another pot.

Old soil isn’t always bad soil: most potting mixes lose structure and nutrition over time but can often be revived. The mix should be discarded if it smells musty, contains mould or shows signs of fungus gnats; compacted roots and depleted nutrients are also problems that argue for replacement.

To refresh usable mix, tip it into a clean container, break up clumps and remove old roots or debris. Mix in around one-third new compost and a handful of perlite or coco coir to improve aeration and drainage, and add a slow-release fertiliser for large tropical plants. 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 writer said they used the refreshed soil to repot a pothos, which sent out new growth within weeks. The verdict given was to refresh when you can and replace when you must, with a little maintenance turning old soil into a healthy base for new growth, the piece added.

Key Topics

Culture, Potting Mix, Pothos, Compost, Perlite, Coco Coir