The Spider Cactus

Plant Stem

• The medium-green squat round stem is covered with five to eight longitudinal rows of gently rounded bumps called tubercles, each bearing an areole and spine cluster. The slightly protuberant bumps look like a projecting chin to some people, so the whole genus (Gymnocalycium) that spider cactus belongs to is known as chin cacti. The tubercles can have a purple tinge in the winter if grown in bright light with some sunshine. Plants can reach 6 inches wide and 4 inches tall.

Flowers and Fruit

• Spider cactus flowers are 2 to 3 inches wide and usually white, although a pink variety exists. The flowers come out of areoles near the top of the plant, and are erect and bowl-shaped. They bloom in spring and summer. Bees pollinate the flowers, and two unrelated plants are needed for cross-pollination. Round black seeds begin to develop in oval green fruits that have a somewhat scaly exterior.

Cultivation

• Grow spider cactus in a shallow pot with drainage holes that is close to the size of the plant's body and roots, with 2 inches to spare around the sides of the plant and underneath the roots. Use a well-draining cactus-potting soil. Allow the cactus to fill out the pot before transferring it to just the next biggest pot size, repotting it in the spring. Don't water it for a week after you transplant it. Then water the plant whenever the top 2 inches of soil become dry, soaking the potting soil so water flows out of the drainage holes. Empty any standing water from the pot's saucer within a few minutes. The growing season is spring through summer, with the plant resting for the winter. Place spider cactus in full sun in cooler, cloudier climates and part shade in hotter, drier climates. Spider cactus is hardy in U.S. Department of Agriculture plant hardiness zones 9 through 11.

Propagation

• Spider cactus usually has a single stem, seldom forming offsets that could be separated and rooted, so plants are grown from seed. Collect the fruits in the fall when they contain mature black seeds. Break open the fruits, and remove the seeds. Put a mixture of moistened 1 part peat and 1 part perlite into a 4-inch nursery container, and sow the seeds on top of the soil. Add a layer of grit. Cover the pot with a sheet of plastic wrap or a piece of glass. Keep the growing mix moist but not soggy. Put the pot in a warm area where it gets bright indirect light, and watch for germination. Remove the cover after germination occurs.