Growing cottontop cactus in a pot

Cottontop Cactus can be grown in a container while young, but it reaches about 5 m, so a pot is a medium-term home rather than a permanent one. Start it in a 40-60 cm (16-24 in) across planter, expect to pot on as it grows, and accept that container life will keep it smaller than it would be in open ground — which is often exactly what people want.

Aim for a container 40-60 cm (16-24 in) across. Pot on when roots show through the drainage holes or growth slows noticeably — usually every 1-2 years for a plant this size. Move up one pot size only; jumping several sizes leaves wet compost the roots cannot reach, and that is what rots them.

Use a quality peat-free compost with a handful of perlite for air, and make sure the pot has drainage holes. Compost in containers compacts over time, which suffocates roots — that is the main reason potted plants decline.

Containers dry far faster than open ground, so cottontop cactus in a pot needs checking more often than the general guidance of "Every 3–5 weeks in summer; completely dry in winter" — especially in summer, wind, or a heated room. Check the top few centimetres with a finger rather than watering on a fixed day.