Succulents and cacti: sun, grit, soak and dry

Succulents and cacti store water in fleshy leaves or stems. That makes them tough in drought and fragile in wet. The Royal Horticultural Society's advice comes down to three things.

Sun: most want the brightest spot you have, such as a sunny windowsill or balcony. Too little light gives pale, stretched growth. Forest cacti such as the Christmas cactus are an exception and prefer softer light.

Grit: use a free-draining, gritty mix, for example two parts potting compost to one part horticultural grit or sharp sand. Choose a pot that just fits; an oversized pot holds wet mix for too long, the same lesson from unit 4, and matters even more here.

Soak and dry: in the growing season, water thoroughly once the surface is dry, let the excess drain away, and never leave the pot standing in water. In temperate winters, the RHS advises watering only enough to stop the plant shrivelling, with cool nights, which also helps many cacti flower. Overwatering can damage roots and cause rot, while underwatering causes shrivelling, so aim for a thorough soak followed by a dry spell.

Handle spiny cacti with folded newspaper or thick gloves when repotting.