Origin and Habitat: Melocactus ferreophilus is a narrowly endemic species restricted to a very small area less than 100 km2 in central Bahia, Brazil.
Habitat: The species grows on raised, exposed limestone outcrops in caatinga forest. It is critically endangered, occuring at a single location, with four subpopulations, two of them are probably extinct, and there is continuing decline in the number of mature individuals and subpopulations, mainly from excavation for stone. Major threats are mining, road construction and the impact of collectors.

Melocactus azureus subs. ferreophilus is one of the rarest of the Brazilian melocacti that distingushes from the standard Melocactus azureus for its green epidermis (never frosty blue) with white wool (never brown) and conspicuous reddish bristles that protrude noticeably from the cephalia.

Cultivation and Propagation: These tropical cacti are not the easiest things to grow and aren’t plants for beginners.
Growth rate: It is a relatively rapidly growing given the best conditions.
Soils: It likes very porous standard cactus mix soil.
Repotting: The root system is weak and generally resents being repotted and can take a long time to re-establish. Use pot with good drainage.
Light: They preferes very bright light, not as much as the most arid growing cacti, but plenty nonetheless. Tends to bronze in strong light, which encourages flowering and heavy spine production.
Watering: Melocacti grow from April to October and cannot endure long stretches of total dryness, and also too much water will rot them, as their weak root systems tends to be inefficient at sucking up water from wet soil. Nonetheless, again as a result of their tropical origins, they need a fair amount of water, but allow the soil to dry quite a bit before watering again.
Hardiness: Melocactus rest from October to April but can’t stand cold, or even fairly cool temperatures, so is indispensable to keep them above 8-12°C at all times, severe damage or death occurring at temperatures that the great majority of cacti wouldn’t mind in the least and prefer more frequent water in winter than other cacti, say once a month. (but hardy to 4 C ° C for short periods). However warmth throughout the year will increase the grower's success ( minimumum12° to 20° C during rest season). In the rest period no high atmospheric humidity!! (Temperature Zone: USDA 10-12)

Some of the information in this description has been found at desert-tropicals.com, llifle.com and cactus-art.biz