Melocactus maxonii ‘Inermis’ – Spineless Turk’s Cap Cactus

Known for its clean, smooth body and distinctive woolly crown, Melocactus maxonii ‘Inermis’ is a striking cactus that stands out in any collection. Unlike other cacti, this species stops growing taller once it reaches maturity and begins forming a cephalium – a woolly, reddish tuft that produces delicate pink flowers. The ‘Inermis’ form has reduced or absent spines, giving it a neat, sculptural look.

Scientific Name
Melocactus maxonii ‘Inermis’ (named after botanist William Ralph Maxon; ‘inermis’ = unarmed or spineless)

Synonyms
None widely used, but occasionally referred to informally as spineless forms of Melocactus curvispinus

Common Name
Spineless Turk’s Cap Cactus, Melon Cactus

Origin
Native to Cuba and other parts of the Caribbean

Light
Bright indirect to direct light is best. A few hours of morning or late afternoon sun will keep it compact and healthy. Avoid intense midday sun, especially when newly moved.

Water
Water only when the soil is completely dry. In summer, this may be every 2–3 weeks. Reduce to once a month or less in winter. Avoid getting water on the cephalium.

Humidity
Prefers low humidity and good airflow. Avoid placing it in enclosed or damp spaces.

Soil
Use a sharply-draining cactus mix. Add extra grit, pumice, or perlite for fast drainage. Avoid organic-rich soils.

Food
Feed monthly in spring and summer with a diluted cactus fertiliser. Do not feed in winter.

Temperature
Thrives between 18–30°C. Keep above 12°C at all times. Cephalium is sensitive to cold and excess moisture.

Pet-safe
No – mildly toxic if ingested. Keep away from pets and children.

Sprouts Top Tips
Once the cephalium forms, avoid repotting – Melocactus dislike root disturbance once mature.

Extras
The cephalium grows slowly but can last for many years, producing tiny flowers and sometimes fruit.

Did You Know?
Unlike most cacti, Melocactus stop producing new body growth once the cephalium appears – all energy goes into flower production instead!