Yes, you can sometimes reuse old potting soil, but only if the soil was previously healthy and free from pests or disease. Over time, potting mixes lose structure and nutrients as plants absorb minerals and organic materials break down. This can leave the soil compacted and less effective for supporting healthy roots.
If the previous plant showed no signs of pests, fungus gnats, root rot, or mites, you can refresh the soil by mixing in fresh potting mix or soil amendments. This helps restore structure, aeration, and nutrients so the soil can support new growth.
However, if the old soil had pest infestations or plant disease, it is usually safer to discard it or sterilise it before reuse. Reusing contaminated soil can easily spread problems to new plants.
Adding amendments such as Ecothrive Life-Cycle can help rebuild soil fertility and improve microbial activity.
For more information about plant nutrition and soil health, see Houseplant Fertilisers 101: Understanding NPK.