Astrophytum asterias [ass-troh-FY-tum] [ass-TEER-ee-as] is a cactus with a disc-shaped body and multiple ribs with white scales.
Due to its distinct appearance, the plant has several common names:
- Sand dollar cactus
- Sea urchin cactus
- Star cactus
Astrophytum asterias is part of the Cactaceae family and the Astrophytum genus.
The genus contains just five other cacti.
Star cactus is native to Texas and parts of Mexico.
It’s no longer common in the wild and mostly found in a single site in Texas.
First cultivated in the 1840s, it’s become a popular houseplant.
Astrophytum Asterias Care
Size and Growth
- Star cactus is a small plant with a round, globular body.
- It reaches a height of just one to two and a half inches and a diameter of 2″ to 6″ inches.
- The disc-shaped body is separated into seven to ten ribs, lined with wooly areoles.
- The body is typically greenish-brown and may become speckled with white scales.
Flowering and Fragrance
A yellow flower with a red base appears from the center of the globe.
The flowers appear between March and June while fruiting occurs between April and June.
The plant produces oval fruits typically green to pink in color.
Light and Temperature
Star cactus is winter hardy in USDA hardiness zones 8 to 9.
In its native Texas and parts of Mexico, it grows easily outdoors under full sun or partial shade.
Outside of its native regions, astrophytum asterias grow best near a sunny window inside the home.
It can’t survive freezing temperatures.
The ideal temperature in the summer is above 70° degrees Fahrenheit (21° C).
During the winter, it can tolerate slightly cooler temperatures.
Watering and Feeding
- As with most cactus, astrophytum asterias does not need frequent watering.
- Water sporadically during the summer.
- During the winter, it shouldn’t need additional moisture unless the temperatures remain warm.
NOTE: The soil should dry completely between each watering.
- Add a diluted liquid fertilizer during the growing season to encourage healthier growth.
- Use a 20-20-20 liquid fertilizer mixed to half strength with water.
Soil and Transplanting
Grow star cactus in standard cactus potting soil or make homemade cactus soil.
For a DIY cactus potting mix, combine:
- 3 parts of soil
- 2 parts sand
- 1 part perlite or pumice
The soil should provide excellent drainage, allowing water to drain away quickly but maintain some moisture.
This helps prevent overwatering.
Repot star cactus cultivated as a houseplant each year to promote additional growth.
Repot in the spring before the growing season starts.
TIP: Wear gloves when handling star cactus to protect against the stiff spikes on the outside of the plant.
While grooming isn’t necessary, removing the flowers after they wilt can help keep the cactus garden or container clean and presentable.
How To Propagate Star Cactus
Propagate using seeds. As the plant features a single globular body, cuttings are not possible.
Obtain seeds from a nursery or harvest them from mature plants.
The seeds are contained in the fruiting bodies appearing after the flower.
Remove the fruit capsule when it ripens and allow it to dry thoroughly.
- Open the capsule to remove the seeds.
- Sow the seeds in sandy soil using a flat container.
- It should contain a higher consistency of sand compared to standard cactus potting soil.
- Amend regular cactus mix with sand to improve drainage.
- Scatter the seeds over the soil and lightly cover with sand.
- Water enough to keep the soil moist until the seeds germinate, which may take six to eight weeks.
- The following year, thin the bright green globes, spacing them about 2″ inches apart.
- By the second year, the small plants should start to develop the characteristics of the star cactus.
- The ridges and white scales should appear.
- At this point, the cactus is transplanted to individual containers or cactus gardens.
Star Cactus Pest or Disease Problems
Star cactus is virtually pest and disease-free and isn’t invasive or considered toxic.
It’s a simple plant to grow with little to worry about.
The biggest threat is overwatering, which may lead to root rot.
If the plant suffers from root rot, it may appear soft and mushy.
It may also develop small sunken spots or black dots near the roots.
- Remove the plant from the soil.
- Trim the rotted roots and lightly dust the remaining roots and the bottom of the plant with powdered sulfur.
- Allow the plant to dry for several days.
- Wait until the cut sections scab over before repotting the cactus.
- Use fresh cactus potting mix when repotting.
- Water thoroughly and allow the soil to dry before watering again completely.
Mealybugs and scale insects may also appear.
Scale insects may be removed by hand.
Use a stream of alcohol from a spray bottle to remove mealybugs.
If these methods don’t work, use a commercial pesticide (Neem oil) to treat the infestation.
Suggested Astrophytum Asterias Uses
Grow star cactus in a cactus garden or succulent garden with a mixture of species.
Place the star cactus closer to the front, preventing taller species from obscuring the view.
It’s also a simple houseplant to grow in any window, adding a small touch of color to any room.