The Bishops Hat Cactus

The Bishop’s hat cactus is a “humane” thornless type of cactus with a strictly geometric shape. Here you will find valuable tips on its care.

Astrophytum myriostigma


The Bishop’s hat cactus belongs to the genus Astrophytum with four to six slow-growing cactus species that grow in arid regions from southern Texas to northern Mexico.

Astrophytum myriostigma grows mainly in the Chihuahuan Desert, which is in the rain shadow of the Sierra Madre.

Because of its symmetrical shape, the Bishop’s hat cactus is also called a star plant or star cactus.


Astrophytum myriostigma grows spherical, and with age, increasingly columnar.

In it’s natural habitat, a maximum height of 40 centimeters is reached, the diameter is a maximum of 20 centimeters.

The body has a strict geometric structure with four or five ribs. Every single rib looks like a broad triangle, the tips meet at the apex. These ribs enable the Bishop’s cap cactus to prevent cracking when water is absorbed.

Astrophytum myriostigma - star shaped cactus
Astrophytum myriostigma – star shaped cactus


On the ribs of the Bishop’s cap there are round areoles at a distance of 10 to 20 millimeters, which look like oval felt-like cushions and are produced instead of thorns. These areoles are reduced leaf systems. The dense white wool flakes protect the Bishop’s hat from harmful UV radiation.

The flowers of the Bishop’s cap (Astrophytum myriostigma) give off a pleasant scent


Between spring and autumn, four to six centimeters long, yellow, funnel-shaped and radial flowers, which often have a red cente, open again and again during the day near the apex.

When sniffed closely, the flowers smell sweet.

The sepals have black tips, the petals are slightly serrated, the stamens and style are yellow in color. The flowers only last a few days. You have to wait at least three years before they show up.

Pretty, scented flowers of Astrophytum myriostigma
Pretty, scented flowers of Astrophytum myriostigma


Reddish berry fruits with a diameter of just over two centimeters develop from the flowers of the Bishop’s cap. When the time of ripening is reached, they burst open in a star shape and release boat-like brown or black seeds.


The Bishop’s hat needs a full sun location, especially in summer the cactus appreciates being outdoors in a full sun that many other plants would not tolerate. A rain cover is strongly recommended.

You should always get it used to the sun gradually so that the Bishop’s hat does not get sunburned if it is placed under the hot afternoon sun.

Indoors, its ideal place is at a south-facing window, and the distance from the pane should be small. The hibernation takes place – well deserved after the flowering – between November and March at temperatures around 10°C (50°F).

As much light as possible is also an advantage in the resting phase.

From its Mexican home, Astrophytum myriostigma is used to summer temperatures around 30°C (86°F) and winter temperatures around 17°C (62°F).

At night the temperature sometimes drops to a few degrees above freezing point, but there is no frost.

Substrate (soil)

Cactus soil with high mineral components such as lava gravel meets the needs of the Bishop’s hat.

The organic nutrient content should go to zero, because there is no humus formation in the desert.

A certain amount of lime is welcomed.

It is essential to avoid waterlogging. Larger Bishop’s hats are therefore given drainage material as a precaution in the base of the pot.


During the main growth phase in spring and autumn, the Bishop’s Cap should be kept moderately moist. The top layer of soil should always dry well between watering, and several sunny days are no problem.

In winter, the watering should be turned off completely.

Cacti can also be watered from the bottom using trays filled with water. In this case, the water absorbs into the soil through the drainage holes and then rises to the surface of the pot. Any remaining water should always be removed.

Waterlogging must be avoided with the Bishop’s hat (Astrophytum myriostigma)


Every three weeks you can enrich the irrigation water with a little cactus fertilizer during the growth phase.


Every two years it makes sense to repot young Bishop’s hats in winter. Older specimens should be disturbed as little as possible.

Clay pots have the advantage that excess water can evaporate through the outer wall.

The pot should be wide, as the roots of the Bishop’s cap spread out rather flat.

After repotting, the cactus should not be turned. A changed direction towards the light usually means that there are no flowers.


Astrophytum myriostigma var. Nudum is completely naked, the wool flakes are missing on the usually five ribs. This variety is naturally much more prone to sunburn.

In the columnar ‘Huboki’ variety, flower buds form, but they do not open, but become side shoots.

Astrophytum myriostigma var. Strongylogonum has less angular, but more pronounced arched ribs.

Astrophytum myriostigma var. Quadricostatum is a shape with four ribs.


The relatively large seeds of the Bishop’s hats are best sown in spring on sharp sand or nutrient-poor cactus soil in shallow pots.

Since these are light germs (needing light to germinate), they are not covered with substrate.

Before sowing, you should moisten the substrate well. Germination takes place after a few days at temperatures between 20 and 25 degrees Celsius (68 -77 degrees Fahrenheit).

A glass plate can be placed over the vessel until the first green shows. A vegetative propagation is almost impossible because there are neither runners nor shoots.

Diseases and Pests

Root mealybugs will always occur if the culture is too moist.

In the case of severe infestation, Astrophytum myriostigma is best potted out and the existing soil carefully removed.

A culture that is too moist can also lead to root rot.

Astrophytum myriostigma with mealy bugs

Janie blogs for Succulent Alley and she loves succulents and cacti.