The mammillaria genus is one of the most numerous among the cacti, in fact it has about three hundred species of succulent plants, all originating in Mexico and South America; they are very particular and showy plants, and have over time obtained the approval of most of the succulent enthusiasts; in fact they are among the most widespread in cultivation, and can easily be found in any nursery, village fair, market stall. The name derives from the term udder, as the stem of the mammillaria does not have ribs, but is completely divided into small more or less elongated udders, with a conical or cylindrical shape; at the apex of each breast there is an areola, generally equipped with spines, erect or arched, often white, sometimes yellow; some species have a single further spine that rises from the center of the areola in the direction of breast growth, this spine is generally hooked in shape. The thorns of the mammillaries are very showy, organized in small combs or tufts, numerous or single, white or dark, often accompanied by a thick white or pink hair. Many mammillarias bloom in profusion in spring, with great ease; the flowers are produced in the youngest part, that is the apical part, and bloom in the axilla which forms at the base of the breasts. Mammillary flowers are usually pinkish, but there are species with white, green, yellow, red and striped flowers; the flowers are followed by a small fruit containing the fertile seeds. Some species have a short period of vegetative rest in August, which is often followed by a second flowering, less abundant than the spring one.
Most species of mammillaria it is small in size, with a round, or briefly columnar, stem which remains below 9-10 cm in height; some can reach 25-30 cm in height, and can develop solitary, branch or sometimes even stick.
The mammillaria originate from areas of the globe characterized by stony and porous soils and by a dry climate, therefore in general they behave like most of the cacti. They should be planted in well-luminous areas, with at least a few hours of direct sun every day, but it is good to avoid the hottest hours or the completely sunny areas, especially in summer, when the direct sun could ruin the epidermis of the plants by burning it; a semi-sunny exposure is therefore chosen, with a veiled shadow in the central hours of the day. The watering will be sporadic and not very generous, to be carried out only when the weather is warm, therefore from April to September; in the months of the year when the climate is cool and the days are short it is advisable to water the mammillaria very little, or even for nothing if the plant is grown in a cold greenhouse, or in any case in a cold place, without heating. In any case, even in the growing season, we water only when the soil is dry, considering that a small earthenware pot left in the June sun may need watering every other day, or every three days approximately; every 15-20 days mix a fertilizer rich in potassium and low in nitrogen to the irrigating water.
The ideal containers for the mammillaria are earthenware pots, of small size, in which we will place a compound consisting of universal potting soil, mixed with pozzolana, lapillus or pumice stone, in equal parts, so as to obtain a well-permeable substrate, free of stagnations. water, harmful to the plant.
These plants, like many cacti, can withstand winter temperatures even close to zero ° C, provided they are kept in a well-dry, moisture-free area, especially in the soil; therefore if in September-October we stop watering the plants, we can try to leave them also on the terrace, on a shelf, or in a cold greenhouse, in a place where they are not in any case reached by the weather water; if we do not have any kind of shelter it is convenient to keep them indoors, possibly in an unheated room, such as a stairwell, where plants receive lots of light and a cool climate; in fact, as happens for most of the cacti, these plants tend to bloom with greater probability if in winter they can enjoy a period of vegetative rest, which is precluded if they live all winter in the apartment, with about 20 ° C of temperature throughout the day.
Some species of mammillaria go through a period of semi-vegetative rest even in summer, in August, a period in which it is best to avoid watering them; they often bloom again when the cool weather arrives at the end of August.