Astrophytum
Small genus, big in cultivation
Astrophytum cacti are extremely popular plants, with easily a hundred or more cultivars around the world. The generally recognized species are:
Astrophytum myriostigma
Astrophytum asterias
Astrophtum capricorne
Astrophytum ornatum
Astrophytum caput-medusae
Conditions in situ
The weather in this region of Mexico tends to have hot, muggy summers and short, dry winters. Using the city of Monterrey to review conditions, summer highs are in the 90F – 95F range, and summer lows are in the 70F range. Winters rarely drop below 40F, with highs in the 70F range.
Looking south to the city of San Luís Petosi, the average highs and lows tend to be milder. Each species has climate conditions they thrive better in, which I’ll cover below.
Location in the wild
These cacti all come from the Chihuahuan desert in Mexico, with some species ranging up into southern Texas. Below is circled the rough area these cacti can be found in the wild.
Astrophytum myriostigma
Found commonly in the states of Nuevo León, San Luis Petosí, and Tamaulipas. The hot season, or growing season, for these is from about May through the end of September, although naturally if conditions are ideal they’ll grow outside of the hottest months of the year. High temperatures are typically in the 90F range during the warm season, with night time lows in the 70s. High temperatures in the cold season are rarely above 70F, and the plants can tolerate brief drops below freezing if kept dry.
In winter, these do best when kept almost entirely dry, especially if night time lows will be approaching freezing.
Care for Astrophytum myriostigma
Basic cultivation: Easy to cultivate summer growing species.
Soil: Use a very well draining mix; if fertilized in summer, these can be grown in an almost entirely inorganic blend.
Watering: Thrives in very dry environmental conditions. When hot, accepts regular water but should not be allowed to sit with soggy roots. Needs to dry completely before watering again. When the weather cools, should be kept almost entirely dry until the weather warms again.
Cold hardiness: Can tolerate temperatures to the high 20sF if kept perfectly dry in winter. Try to keep ambient humidity dry, if possible, over the winter rest period. High ambient humidity can lead to rot.
Fertilizing: A low nitrogen fertilizer is recommended; I use a cactus-specific fertilizer at half strength along with Super Thrive roughly once a month through the growing season.
Sun exposure or lighting: Can be grown in light shade to full sun. More sun leads to better coloration; not enough light leads to etiolation and makes plants significantly more prone to rot.
Propagation: Entirely through seeds; they bloom frequently through summer and produce plentiful seeds. Often grafted to faster growing species to get them to a suitable size to sell.
Popular / Common Cultivars
- nudum (no white dots)
- quadricostatum (4 sided)
- tricostatum (3 sided)
- variegated
- onzuka (snowy-white, heavily speckled)
- harder epidermis than typical astrophytum; prone to cracking if overwatered
- Fukuryu
- type A: more common, has partially developed extra ribs that do not reach the plant apex
- type B: rarer, has many more ribs and ‘warts’ that reach all the way to the top of the plant
Astrophytum asterias
Once, these plants were found throughout Texas and Mexico, but much of the original habitat has been destroyed. In the wild, it is now found almost entirely in one tiny spot near Rio Grande City.
In their natural range, they are low growing cacti that are commonly found in the shade of other plants. Wild plants are very well camouflaged, and grow nearly half submerged in substrate, often covered by sand.
They are summer growers, and do well in warm temperatures (90F+), but need to be protected from intense sunlight in hot weather. During winter, they should be kept fairly dry, and due to the altitude they are adapted to, they’re surprisingly cold hardy.
Caring for Astrophytum asterias
Basic cultivation: Easy to cultivate summer growing species.
Soil: Use a very well draining mix; enjoys a mineral mix. Can be grown in nearly full inorganic medium if fertilized during the growing season.
Watering: Thrives in very dry environmental conditions. When hot, accepts regular water but should not be allowed to sit with soggy roots. Needs to dry completely before watering again. When the weather cools, should be kept almost entirely dry until the weather warms again.
Cold hardiness: Can tolerate temperatures to the low 20sF if kept perfectly dry in winter. Somewhat frost hardy, but most growers avoid this for best appearance.
Fertilizing: Fertilize very little; while slow growing with little supplemental feritlizer, this slow approach leads to the best appearance in older plants.
Sun exposure or lighting: Does best with very bright, but indirect light. Too much light will burn the plant.
Propagation: Entirely through seeds; they bloom frequently through summer and produce plentiful seeds.
These plants rarely get more than 6″ across, and are prone to becoming “senile” as they approach larger sizes. Older plants should be repotted every 2 to 3 years at most, while younger plants can benefit from more frequent repotting.
Popular / common cultivars
- “star type” – deep indents between each wedge; giving the cactus a distinct star shape
- nudum – lacking the white tufts of hairy “scales” typical for the species
- variegata – variegated
- Fukuryu – extra ribs; usually does not reach the plant apex, and is no where near as warty as the myriostigma form
- Ooibo – very large and fluffy areoles compared to a typical asterias
- Superkabuto – significantly more white fuzzy coverings compared to a typical asterias, sometimes entirely covered by fuzz
- Kikko – raised tubercules along the edges, resembing a turtle shell
- Akabana – red flowers
- Hakuun – name means “cloudy sky” and the epidermis has patchy white, cloud-like pattern
Astrophytum capricorne
These distinct looking cacti are native to the Chihuahuan desert, which ranges from New Mexico, Texas, and Northern Mexico. There are a number of subspecies and cultivars, but the most commonly available species is the standard A. capricorne.
They thrive in bright, direct sunlight with high temperatures and regular watering. In winter, keep cool and dry, protected from high humidity or rainfall. If kept perfectly dry, they can survive a light frost, but prefer warmer temperatures.
In Cultivation
Basic cultivation: Easy to cultivate summer growing species; thrives in extremely hot, bright conditions.
Soil: Use a very well draining mix; the hotter it’s grown, the more organic medium it will tolerate.
Watering: The hotter it is, the more water they will take. In temps above 100F during the day, you can water as often as every few days if the soil dries out (although less water is recommended). Keep entirely dry in winter.
Cold hardiness: Can tolerate temperatures to the low 20sF if kept perfectly dry in winter. Somewhat frost hardy, but most growers avoid this for best appearance.
Fertilizing: Fertilize very little; dilute to at most half concentration and feed only during the growing season.
Sun exposure or lighting: Prefers very bright light, almsot full sun. If acclimated over time, can take full sun exposure, but needs to be slowly introduced or it will burn. The more sun it is exposed to, the better the spination.
Propagation: Entirely through seeds; they bloom frequently through summer and produce plentiful seeds.
Popular / Common Cultivars
- var. senile – smaller, more grass-like spines
- crassispinoides – selectively bred for white, almost clear yellow spines that are weak, as well as a yellow flower
- crassispinum – very sharply ribbed, stem brighter green and lacking in white dots, spines are noticeably thicker, stronger, and larger than typical capricorne
- var. minor – aka minus – small growing, flowers large with brilliant orange-red throat, fine, thin spines
- var. niveum – rigid thorns, significant “flocking” of white flecks, similar to A. asterias or myriostigma
- rosa – pinkish flowers with red center, spines are dense and almost completely cover the body
- buffalo spine aka “Taiho-gyoku” – notable by the less curved spines that are thick, lumpy, and almost monstrose compared to typical spines. Becomes more pronounced in increased sun.
Astrophytum ornatum
Large, distinctive cacti native to Hidalgo, San Luis Potosi, and Guanajuato, Mexico.
They thrive in bright, direct sunlight with high temperatures and regular watering. In winter, keep cool and dry, protected from high humidity or rainfall. If kept perfectly dry, they can survive a light frost, but prefer warmer temperatures.
In Cultivation
Basic cultivation: Easy to cultivate summer growing species; thrives in extremely hot, bright conditions. Slow growing, and can take up to 10 years to be large enough to bloom.
Soil: Use a very well draining mix; plenty of inorganic medium. Good drainage is essential.
Watering: Water when dry during the growing season, keep dry through winter. Water during cold months makes them prone to root rot.
Cold hardiness: Can tolerate temperatures to the low 20sF if kept perfectly dry in winter. Somewhat frost hardy, but most growers avoid this for best appearance.
Fertilizing: A dilute cactus fertilizer during the peak of growing season is appreciated. Doesn’t need much.
Sun exposure or lighting: Prefers very bright light, even full sun. Needs good ventilation and air movement to thrive.
Propagation: Entirely through seeds; they bloom frequently through summer and produce plentiful seeds.
Astrophytum caput-medusae
Critically endangered species native to a single location in Nuevo Leon, Mexico, where it is somewhat abundant in its tiny growing range. The area it is native to is less than 100 square kilometers and heavily threatened by poaching and livestock damage.
In Cultivation
Basic cultivation: Easy to maintain in summer months when potted in appropriate soil, but prone to rot in the winter if watered. Lighting needs vary but thrives best in bright, indirect light.
Soil: Use a very well draining mix; plenty of inorganic medium. Good drainage is essential.
Watering: Water only in the active growing season, when nights are above 50F, and the soil is dry before you offer water. Seedlings (less than 3 years) need some water in winter, maybe once a month, but older and larger plants should be kept nearly bone dry or they will rot.
Cold hardiness: Resistant to frost if kept dry, but should be kept protected in a greenhouse over winter to prevent winter rain or snow from offering too much moisture. Fine down to high 20s.
Fertilizing: Dilute balanced fertilizer at the start of growing season (in San Diego, around June/July) can be appreciated and encourage blooming. If freshly potted in new soil, no fertilizer needed the first year.
Sun exposure or lighting: Bright indirect is best. If grown outdoors, keep in nearly full shade, ideally with direct sun only for a few hours in the morning.
Propagation: Entirely through seed. Will bloom in the summer with huge, yellow flowers that clearly resemble other Astrophytum and indicate why they’re in the same genus.
