Astrophytum asterias is an unusual-looking cactus that grows well as an indoor plant. This round cactus goes by the easier common names of Star cactus, Astro cactus, Sea Urchin cactus, or Sand Dollar cactus.
It thrives in bright, indirect light and requires minimal watering, making it a low-maintenance and visually captivating addition to any indoor space.
The spineless dome-shaped olive-green body of the Astrophytum asterias has eight symmetrical segments. Each segment has small tufts of white hairs. Star cacti stay small. Indoors they rarely grow more than four inches across.
Related reading: Astrophytum myriostigma care.
Indoor Astrophytum Asterias Care
The star cactus is native to Texas and northeastern Mexico where it grows in warm and dry conditions with plenty of bright sunlight.
Astrophytums make excellent houseplants. They are easy to grow indoors with minimal care.
Want to buy an Astrophytum Asterias star cactus? Find them for sale on Amazon.
Light Requirements
The star cactus likes lots of light. Indoors, they do best in a bright, sunny window with 6 to 8 hours of sun. If you can not give your plant enough natural light, consider getting a grow light.
Avoid too much direct afternoon sunlight, especially on hot summer days. Protect your plant through the hottest midday hours. Dry, brown spots can be a sign of sunburn. Move your plant further away from the window, or filter the light with a sheer curtain.
Watering
Astrophytum asterias are very drought-resistant. In their native habitat, they go through long dry spells followed by heavy rain. They store water inside while waiting for the next rainfall (or indoor watering).
Don’t water your star cactus too often. Overwatering is the most common problem with these plants and can lead to root rot.
If roots rot, they lose the ability to absorb water and thus can’t supply any water to the plant. The body of the plant should feel firm but will become soft and mushy inside when overwatered. You might notice brown rotting at the base.
Indoors, allow the soil to dry out in between waterings. When you water, be generous with it. This is called the soak-and-dry method. Soak the soil when you water, then let it dry out completely before watering again.
Only water your star cactus like this in spring and summer. Slow down watering in autumn and don’t water in winter. Keep it bone dry until spring.
If you are unsure when to water, you can use a moisture meter to help.
Related reading: the basics of how and when to water your cactus plants.
Soil and Repotting
If your star cactus has outgrown its pot, repot it in spring in a pot one size bigger than the original. It is a slow grower so you won’t have to repot more than about once every 2-3 years.
Plant in a very fast-draining potting mix. You can purchase a premixed gritty succulent mix. If you want to prepare your own, use just a little bit (not more than 1/3rd) succulent soil. Mix in a lot of pumice and grit to help aerate the soil and improve drainage.
Make sure the new pot has drainage holes on the bottom. Without those, excess water has no way to get out and will drown the roots.
Terra-cotta pots are preferred. Clay pots are porous helping the soil to dry out quicker. Whereas plastic containers hold moisture inside, keeping the soil damp.
Related reading: How to repot cactus plants.
Flowers on a Star Cactus
Throughout summer, the Astrophytum star cactus can grow large, yellow flowers with orange red centers.
For the best chance of flowers growing on your indoor star cactus, keep it dry during winter, and don’t move your plant too much in spring and summer. Put a mark on the container so you can put it back in the same way after watering.
Astrophytum plants can bloom multiple times during the growing season. Each flower only lasts for two or three days. The older the plant, the more blooms it grows each year.
Star Cactus Propagation
You can propagate a star cactus from seed. Purchase good quality seeds or, if you are lucky and your plant has flowered, you can collect seeds from the spent flowers.
Use seeds as fresh as possible, and plant them quickly after harvesting. They don’t tend to keep well for a long time.
- Fill a tray or container with fresh rooting potting mix.
- Sow the seeds about half an inch deep and an inch apart.
- Cover each pot with plastic to retain humidity and warmth.
- Place in a bright, warm location (no direct sun), and keep the medium slightly damp.
- Allow air into the container every day or two by removing the plastic for a while and wiping off condensation.
- Completely remove the plastic when the seeds have germinated.
- When the baby cacti are large enough to handle, transplant them into small individual pots and start regular care.
Related reading: 6 different ways to propagate all your plants.
Star Cactus Endangered Species
The number of Star cacti in the wild is declining with the fear of them becoming extinct.
The rare Astrophytum asterias cactus is found only in small parts of northern Mexico and Texas. It’s believed there are just about 2000 of these cacti left in the wild. This is based on the latest global status reviewed back in 2015. So nowadays it might be even less.
Poachers started digging up the plants in the wild to sell to stores. Combined with habitat loss by urban development, and different diseases and herbicide use, the star cactus is disappearing from the wild.
This has led to Astrophytum asterias becoming classified as vulnerable to extinction by the International Union for Conservation of Nature. It is also listed as endangered by the US Fish and Wildlife Service. and critically imperiled by The Nature Conservancy.
Because of all this, it is now listed in the CITES Appendix I, as threatened with extinction, and international trade is illegal.
The star cactus is being cultivated as a houseplant allowing it to survive. Those offered for sale should all be grown either from seed. Make sure to buy your plants from reputable sellers.
Plant Pests
The Astrophytum asterias is not very prone to pests, but can occasionally be affected. Watch out for mealybugs and scale insects. Inspect your plant regularly for signs of bugs to catch a possible infestation before it becomes severe.
Related reading: What to do about common houseplant pests.
Is the Star Cactus Toxic to Cats?
Astrophytum asterias are considered non-toxic. It is safe to grow the star cactus at home around your cats or dogs.