Photo Courtesy: Britannica.com
If you’re planning to grow a living rock cactus, you’ll be doing a noble task to the nature, because this amazing species of cactus is fast being depleted from the earth by plant collectors, grazing animals or urban growth. There are six living rock species of which we’ll be discussing here the Texas living rock cactus i.e., Ariocarpus fissuratus. Other five species are native to Mexico. All living rock species are protected not only by the U.S. and Mexican governments, but also by CITES, i.e. the Convention on International Trade in Endangered Species of Wild Fauna and Flora, which has listed them as endangered species.
How does Texas Living Rock Cactus Look?
From the name, you can imagine that this species looks like rock. It appears like a pile of gray-brown-green rock chips evenly spread on the surface of the earth. They don’t spread quick enough to restore population and hence their status in the wild is threatened due to the reasons given above.
However, the Texas living rock cactus is extremely sought-after among cactus lovers because of their exceptional growth patterns, large, beautiful flowers and their rarity.
All living rock cacti look like each other. CITES has declared the entire genus as under threat. The cactus has a large turnip-shaped root that bears a top containing firm, warty tubercles with a tuft of wooly hair in the center of the plant. The tubercles grow in a rosette pattern and are yellowed with age. They vary in shape depending upon the species. Some are flat whereas others are protruding. The diameter of the plant is around 6” and height is hardly above the soil surface.
Flowers are large, funnel-shaped, 1”-2” in diameter, and arise in fall, amid the wool. Depending on the species, the color of the flower may be yellow, magenta, pink, purple or white. They are followed in the summer by seed pods that remain tucked among the tubercles. Seeds are black, pear-shaped.
In nature, the plants live in severe conditions. They camouflage so well that they are almost invisible.
The Texas living rock cactus has contractile roots. In extreme heat and dryness, they pull the plant below the soil surface.
Texas living rock cactus grows from seeds. But the seedlings grow so slowly that they take years to reach flowering size and further years more to attain specimen size. Therefore, growers prefer to graft seedlings to speed up the growth process. However, you shouldn’t collect cuttings or root pieces from the wild. If you can only get cuttings from another collector, use them to grow your own living rock cactus.
Although three of the living rock species (A. kotschoubeyanus, A. retusus and A. fissuratus) are widespread, new plants don’t tend to spread very rapidly or far from parent plants. Native habitats of two other species (A. bravoanus and A. agavoides) are so restricted and their spread is so slow that both of them are almost extinct in the wild.
How does it Reproduce in the Wild?
In the nature, living rock seeds often remain inside the dried fruits tucked among the tubercles for years without getting separated from the mother plant. But they are viable for several years and become free when the mother plant dies. Because of this, the spread of the plant is slow. Maria C. Mandujano and Concepcion Martinez-Peralta of the Universidad Nacional Autonoma de Mexico studied the reproduction process of Texas living rock cactus, and found that these plants need cross-pollination in order to produce a good seed set. Bees are needed by flowers for pollination and flowers are destroyed in high numbers by flower-eating beetles. These factors are involved in reducing the ability of the plants to spread.
How to Grow?
The potting mix should be a well-draining cactus soil mix. Any mix containing peat should be avoided as it is damaging to the roots. If you can, create a potting medium similar to the soil where these plants grow naturally. It should be around half coarse sand, 30% heavy clay loam and 20% limestone chipping. As a part of the sand, use pumice and also add a bit of slow-release, high-potash granular fertilizer.
Light and Temperature
Living rock cacti are hardy to the U.S. Department of Agriculture plant hardiness zones 9 through 11. They are typically grown as container plants so as to get good drainage and protection from winter cold. As such, they can tolerate temperatures as low as 25-degree F (-4 degree C) because they’re so low-growing. Plants need bright light or full sun in cooler climates.
Large containers, preferably of flexible plastic, are required to accommodate the enlarged roots. They should also have plenty of drainage holes in the bottom. Roots can swell and grow as they absorb and store water. This can cause breakage of terracotta pots.
Living rock cacti do need water during the growing season, but not as much as most other cacti. Once the plants finish blooming and gone to seed in the late summer, you should not water until spring.
The plants also withhold water in winter because they store it in the roots throughout the winter.
You should also make sure the water you provide to the plant is either rainwater or purified water, particularly if in your area, tap water contains many chemicals.
Overhead watering should be avoided.
Bottom watering is the best, but you should not allow the plants to sit in water for longer than half an hour.
If you notice salts crystalizing on the soil surface around the plant, do top watering thoroughly to wash excess salts.
Fertilize in early spring and mid-summer with a water-soluble solution of high potash and phosphate content of one-quarter strength. Ariocarpus cacti do need soluble calcium and a range of minerals. However, you should take care of not using calcium hydroxide (i.e., horticultural or hydrated lime) because it can damage the plants’ roots. Using dolomitic limestone instead is useful as it delivers both calcium and magnesium as soluble bicarbonates.
The plants won’t spread unless the growers can cross-pollinate the plants, collect the seeds and sow them.
You should repot every couple of years by just moving up to the next larger-sized container. But before repotting, wait until the soil is dry around the roots. Make sure you shake off the old soil completely and replace it.
The slow-growing living rock cacti don’t need much of maintenance. You just have to cater their needs for temperature, light and water, and they’ll effortlessly maintain their good looks.
Pests and Diseases
Living rock cacti are generally affected by the same pests that attack other cacti. These include scale insects, mealybugs and similar.
Pest invasion can be best prevented by delivering a preventative dose of systemic insecticide in the first watering of the spring and again in late summer.
With age, plants become more vulnerable to diseases and weakening of the roots, and in such a case, the plant may die suddenly. You can lengthen your plants’ life by prolonging the period between repotting to three years and by stopping watering a little more often. Brighter sunlight may also help.
Word of Caution
Living rock cacti contain toxic and bitter alkaloids as a protection from herbivorous animals. Hence you should keep your pets away from these plants.
So, have you started looking for the beautiful Texas living rock?