Melocactus azureus - Blue melon cactus

Melocactus azureus, sometimes called the blue melon cactus, is a botanical species sought after for its blue-grey colour and for its cephalium; it develops a terminal pink to reddish felt when mature, from which the flowers and fruits emerge. This decorative indoor cactus species is well-characterised botanically. It thrives in very bright rooms, heated all year round, or in a warm temperate greenhouse. It is also interesting for its unique growth habit, very different from more common cacti.

Belonging to the Cactaceae family, Melocactus azureus is a species described in 1971, endemic to the state of Bahia in Brazil. It grows in the seasonally dry tropical biotic region of the Caatinga, on well-exposed rocky limestone outcrops. Botanical synonyms are reported in the literature, notably Melocactus krainzianus.
The plant forms a stem that is initially globose, becoming more or less cylindrical with age, 14 to 30 cm in height and 14 to 20 cm in diameter, sometimes more in older specimens. It has 9 to 10 deep midribs. The epidermis is frosted blue to blue-grey, or even slightly glaucous, depending on growing conditions. The robust thorns are initially reddish black, then take on a greyer hue as they age. On the mature stem, a pinkish-reddish terminal woolly and silky cephalium appears, which continues to grow while the body of the cactus changes little. The small, pink to magenta flowers measure about 1.5 to 2.3 cm in length. In the wild, they are followed by elongated, white to pale pink fruits. As with other Melocactus, the presence of the cephalium signals that the plant has entered its adult phase.

Indoors, this species requires very bright light, a few hours of direct sunlight, a constant temperature between 18 and 30 °C, and a dry or moderately humid atmosphere, around 40 to 60%. It tolerates cold poorly and proves more sensitive than many other cacti to temperature fluctuations and persistent humidity around the roots. It is therefore not the easiest cactus for beginners.

To accompany it, choose species that also enjoy strong light and a dry regime, for example, Gymnocalycium saglionis, Ferocactus glaucescens ‘Inermis’, Astrophytum myriostigma and Echinocactus grusonii.