About the genus
The first Mammillaria was described in 1753 and today there are more than 200 accepted species. Over the years hundreds more have been named, only to be discarded as being not sufficiently different from existing species.
The great majority of Mammillaria are found in Mexico and in Texas and south-western USA. There are some outliers in the Caribbean and in northern South America. Habitats range from sea-level up to about 3,000 metres.
Mammillaria are relatively small cacti and many different forms are to be found. Some are globular and remain solitary all their lives, miniatures barely reaching 5cm diameter, and others, still solitary, can reach 25cm.
Many species will quickly form multi-headed clumps but remain globular. Other species whether solitary or clumping will become cylindrical.
There are great differences in the spines, some so tiny that one needs a lens to confirm that they actually are spines while other species have spines up to 4cm long. Spines may be straight or hooked. The flowers appear in a ring near the crown of the plant.
How to grow them
Mammillaria are happy growing in a mixture of two parts John Innes compost and one part grit, or one part John Innes, one part multi -purpose compost and one part grit. Proprietary brands of cactus composts are fine, too, as one would expect, but are rather expensive in small quantities. The occasional use of commercial cactus fertiliser or general high potash preparations is beneficial.
Plants should be watered from spring to autumn, and a rough guide used by some growers is to start when the clocks go forward and stop when they go back. Some new-comers are disappointed that a watering frequency is not specified but so much depends on the weather, pot size and the compost mixture. The best guideline is that if you go to water a plant and it is still wet, then come back another day.
The plants do well on a windowsill, in a porch or in a greenhouse. A minimum winter temperature of 3°C is satisfactory for the majority. Notable exceptions are the Caribbean plants which need 10°C.
The great majority of Mammillaria flower during May to August, tailing off as autumn progresses. There are some species, e.g. M. plumosa and M. hernandezii, that may flower in December, and the flowering year can begin in March with the likes of M. picta, M. densispina and M. sanchez-mejoradae vying for first place.
Mammillaria are readily grown from seed and a windowsill is fine for this. Seed should be sown on the surface, not buried and the pot enclosed in a polythene bag. Recyclable plastic containers can also be used. Some species will flower in little more than two years.
Popular plants for new growers:
M. moelleriana: usually remains as a single head,
M. surculosa: scented flowers,
M. elongata: clumps readily,
M. marksiana: a popular and easily-obtainable plant,
M. laui subsp. dasyacantha: can flower when only 2cm in diameter and grows quickly.
The great variety in form and convenient size contribute to their popularity. Many species are easy to grow but there are also some that seriously challenge the most expert of growers.
Text and photos: Alasdair Glen
No part of this article may be reproduced without permission. Copyright BCSS and the Author 2019