Red-Headed Irishman thrives in well-drained potting soil

March 13, 2019

Think of Ireland and you think of green, but you may want to think of red. In Ireland, about one out of 10 people has red hair, the highest concentrated population of redheads in the world. Red hair goes way back; even some Neanderthals had red hair. And the hot-tempered Irish might not be a myth; research shows that people with red hair need higher doses of anesthetic.

So it is fitting that Mammillaria spinosissima, a beautiful globular cactus with brilliant red-orange flowers, is affectionately called the Red-Headed Irishman cactus (Mammillaria spinosissima).

This Mexico native will form clumps of columns with red spines. The gleaming flowers form circles atop the stems in late winter and spring.

As a houseplant, this cactus is easy to grow and can grow well even if neglected. Like all cactus, the Red-Headed Irishman thrives in potting soil mixed with sand, which helps it drain well, with a neutral to acidic soil pH. These cacti tend to grow low to the ground, often forming groups or clusters. The wooly stems are covered with tiny bristles. Keep it away from drafts in full but not direct sun.

Only water your Irishman once every two to three weeks, During the winter when light is lower and most growing stops, you can keep the cactus fairly dry. Because they need no pruning they are easy to care for as patio or potted plants.

It is always good to have lots of Irishmen around, so you can propagate Mammillaria spinosissima by gently breaking off new baby plants, or offsets. You can also grow them from seeds sown in early spring. Start fertilizing when new growth appears. Use a low-nitrogen fertilizer such as 2-7-7 diluted to half strength. Apply the fertilizer until the soil is thoroughly moist. Only fertilize every eight weeks, or two or three times during the growing season. Do not overfertilize cactus, as you can kill them.

After a few years, you may have to move your Red-Headed Irishman into a bigger pot. Repot cactus in the spring. Use a new pot that is just one size bigger than the pot it is growing in. If you use a pot that is too big, the soil will hold too much water and cause the roots to rot. For the same reason, terra cotta pots are better than plastic because the clay pots let the soil dry out faster.

These cacti often grow offsets along the base of the plant. Use a clean, sharp knife to cut these baby cacti. Let the cut surface dry out for a couple days to form a callus. This keeps the new plant from oozing sap and rotting. Set the new offsets on the top surface of moist, sandy potting mixture. Keep them out of direct sunlight for the first few weeks. Late spring or early summer is easiest time to root offsets, because the cacti are starting their fastest growth.

For Saint Patrick's Day, or all year long, try growing your own Red-Headed Irishman cactus, and your friends will be green with envy.

  • Paul Barbano writes about gardening from his home in Rehoboth Beach. Contact him by writing to P. O. Box 213, Lewes, DE 19958.