Golden Barrel Cactus problems — and how to fix them

The most common cause of death. A soft, mushy, discoloured base and a foul smell signal rot. Always let soil dry fully between waterings, use a gritty mix and a pot with drainage, and water far less in winter.

Insufficient light makes the body grow soft, elongated and pale, losing its tight globe shape. Move to the brightest possible window or supplement with a grow light; etiolated tissue will not revert.

Despite loving sun, an unacclimated plant moved suddenly into intense direct sun can develop yellow or brown scorched patches. Increase exposure gradually over a couple of weeks.

Watch for white cottony masses (mealybugs) or small shell-like bumps (scale) in the ribs and crown. Dab with a cotton swab dipped in 70% isopropyl alcohol, then treat with neem oil or insecticidal soap.

Brown-black marks form when water sits in the crown combined with cool, damp, stagnant air. Improve airflow and always water at the soil line rather than over the top of the plant.

Cold is only tolerated when the plant is dry. Wet soil plus cold causes collapse and rot. Keep it above 10C (50F) indoors and never let it sit in cold, soggy compost.