Astrophytum myriostigma is probably the most popular species of astrophytum. Its completely distinct look, as the name indicates, resembles a bishop’s hat. Although with age it takes on a more columnar appearance, reaching 2’ in height and 8” in diameter. Like asterias, it is spineless, another feature which sets it apart from other cacti. These seeds will produce ornamental plants with thick, green bodies that are heavily speckled with white. The root of the name astrophytum refers to the stars, as in the word “astronomy,” which reflects a somewhat star-shaped appearance that is characteristic of cacti in this genus. Astrophytum myriostigma is typically found at high altitudes in central and northern Mexico.
Astrophytum myriostigma is cold hardy to about 20 degrees Fahrenheit. For best results it should be given light shade, although it will tolerate full sun. During the summer it should be given moderate water and fertilizer, but it should be kept dry starting in October. An alkaline, porous soil will provide necessary drainage, and watering from below potted cacti so the water wicks up through the soil is recommended. Grafting will also help by lifting the cactus out of the soil where it may come into contact with standing water. Grafting on to faster-growing root stocks such as pereskiopsis, San Pedro and blue myrtle will also speed up growth
Seeds should be germinated in a fine sandy soil at about 70-75 degrees. A commercial potting mix with the larger material strained out is ideal. Flatten out the soil and then put a thin layer of loose soil above it. Sow the seeds on the surface and press in very lightly. They need light to germinate. Mist the soil to keep it moist and cover with clear plastic. Ideally, the covering should not be flat across the top because it will cause the water to drip back on the young seedlings, which sometimes causes rot. Something like a sandwich bag often makes a better “tent” because the water will run down the sides more easily. The soil should not be allowed to dry out while the plants are seedlings. Use a mister if the soil does get dry. Place the seedlings on a heat mat (ideally) and in bright light. Placing the seeds just a few inches from fluorescent lights is ideal for starting seedlings, although natural light will work too. Note that using a heat mat will cause more evaporation, which may require more attention. Be sure to air out the seedlings once a day for best results.