Repotting Calculator

The clearest sign is roots growing out of the drainage holes or circling the surface of the soil. Other signs include: the plant drying out very quickly after watering (the root mass has displaced most of the soil), a pot that's cracking under root pressure, or a plant that hasn't grown despite regular fertilising during the growing season. Most plants need repotting every 1–2 years.

Go up by 2–5cm (1–2 inches) in diameter — not more. A pot that's too large holds excess moisture around roots before they can absorb it, leading to root rot. The exception is very slow-growing plants like succulents and cacti, which prefer to be slightly pot-bound and often only need the same-size pot with fresh soil.

Spring is by far the best time to repot most houseplants. Plants are entering their active growing season, which means they'll quickly establish new roots in the fresh soil. Early summer also works well. Avoid repotting in autumn and winter when plants are dormant — the disturbed roots won't recover quickly and may rot in slow-draining cold soil.

This depends entirely on your plant type. Succulents and cacti need very fast-draining soil with added perlite or coarse sand. Tropical plants do well in a general potting mix with some added perlite for drainage. Orchids need specialist orchid bark, not soil at all. Ferns and moisture-loving plants prefer a peat-free mix with added moisture-retaining materials.

Water lightly 1–2 days before repotting — moist soil holds its structure and protects roots during removal. After repotting, water thoroughly to settle the new soil around the roots and eliminate air pockets. Then wait until the top 2–3cm of soil is dry before watering again. Don't fertilise for 4–6 weeks after repotting as the fresh mix usually contains enough nutrients and the disturbed roots can't absorb fertiliser efficiently.