The bishop's cap; Astrophytums
Cactacea of Mexican origin, to the genus astrophytum belong few species, but given the beauty of these cacti, over time they have been selected hybrids and cultivars, with a particular or even bizarre appearance. They have a globular shape, only large specimens become columnar; the growth is very slow, especially in some species, which have become particularly sought after and expensive. All the species are constituted by ribs, more or less evident, which divide the cactus into 5 segments; the stem is green, variously dotted with white, with hairy areoles, which can also carry thorns. The most typical species is Astrophytums miriostigma, a dark-colored cactus, with many small white dots, hairy areoles along the ribs, without thorns.
Other widespread species are Astrophytums ornatum, which has long thorns in the areolae on the ribs, and astrophytum asteria, a must for collectors, with flat ribs and small hairy areoles; astrophytum asterias is very slow growing, and specimens with even only 6-7 cm in diameter have already many years.
Cacti lovers have produced many astrophytum hybrids, the most famous is astrophytum asterias "kabuto" characterized by many white dots that make the epidermis almost blue. Astrophytum miriostigma is also very common with 4 ribs, or even with three.
If cultivated well these cacti bloom every year at the apex of the stem, producing large pale yellow flowers.
These cacti are decidedly adapted to live in arid, desert or sub-desert areas, and often the fundamental problems that are encountered when cultivating them are related to water: they prefer very dry soils, without any stagnation.
To get a healthy plant surely the starting point is the soil, which must be very well drained, so that the water flows freely; it is generally used in universal soil, mixed with little sand and pumice stone, or pozzolana, in order to have a free and incoherent substrate. They are plants that love alkaline soils, and therefore generally the universal soil tends to be excessively peaty and acid. In most Italian regions the aqueduct water is decidedly very calcareous, and therefore naturally tends to raise the pH of the soil of our plants; so in this case, instead of hindering us, it helps us to make the soil of our astrophytum alkaline. They are slow-growing plants, so it is not necessary to repot them too often, it can also be enough every 3-4 years.
The pots are positioned in a very bright and sunny place, except the asterias species, which loves the bright half-shade, with a few hours of direct sunlight every day; from March-April to September-October, they live outdoors, although it is good to check that they do not receive excessive amounts of water in areas with humid climate and frequent rainfall.
During the winter they move in a cold place, but without frost; a cold greenhouse is ideal, where the climate remains cool but without frost or excessively rigid temperatures.
If we do not have a cold greenhouse we can also simply keep our astrophytum on the terrace on a shelf, covering the shelf with the woven fabric; in this case it is essential that the terrace is exposed to the south, and that the plant finds behind it a wall of the house, where it receives a little heat from inside.
If we do not have a cold greenhouse, nor a terrace, we place our plants in a luminous stairwell, possibly unheated. Often plants kept at home during the winter, with a mild and warm climate, tend not to bloom, and to be more prone to attack by pests.
Water an astrophytum
Certainly the biggest problem encountered with these and other cacti is related to humidity; they come from places where the rains are episodic and sporadic, and the insolation is very high, and are therefore characterized by long arid periods, punctuated by very short very wet periods.
Certainly during the cold period the problem does not occur, we leave our plants dry, especially if they are in a cold greenhouse; for safety, to ensure that the soil is dry when the cold comes, we begin to thin out the waterings at the end of summer, suspending them already at the beginning of September or October.
In the other months of the year we water sporadically, but only when the ground is definitely very dry; so we may have to water once a week in spring, but maybe even 3-4 times a week in July, when the days are very long and sunny, without rain.
Watering will be sporadic, but we always remember that succulent plants are suitable for living in a dry climate because they store water in their tissues; this means that anyway somewhere the water must take it. If we leave our succulents completely dry all the time, or if we water them with a few drops of water that immediately flows away into the vase, the plants will not have enough water to vegetate at best. So in summer, when we water the succulent plants, we use abundant amounts of water, so as to moisten the soil well, avoiding to soak it. If we have a good quality soil, suitable for succulent plants, excess water will flow away, but the soil will be moist: if we put on a finger we feel it moist and fresh.
With the sun and heat the water will evaporate quickly enough; when the soil is dry we can water again.
The time of day when we water is very important: the direct sun tends to heat the earth a lot, especially if contained in small pots; if we water it during the day the water will evaporate very quickly, creating a strong thermal shock to the plant's roots; this happens even if we water in the evening, because pots and soil remain hot for a few hours before dispersing all the accumulated heat, even when the sun is no longer high in the sky. So the best time to water the succulents in the summer is early morning, when the ground has cooled all night.