Ariocarpus trigonus is a plant that looks like it has been built from stone. It consists of whorls of branches, between which are small thick leaves and tiny spines. The effect is very striking: the entire plant resembles a larger version of an Easter cactus or Homalocephala ‘Blushing Bride’.
Origin of Ariocarpus trigonus
Ariocarpus trigonus is found in the colder regions of northern Mexico and the United States. It grows on limestone or rocky soil, with coarse sand or gravel in a dry desert environment at 1000 m (3000 ft) above sea level. The plant will only grow when there is plenty of water available.
Ariocarpus trigonus gets its name from the triangular arrangement of leaves and branches. Unlike most succulent plants, it has no taproot: instead, a woody stem is formed by tightly wrapped layers of tissue. Its entire body is covered with spines that are in rows along the branches.
The flowering season runs from October to February, but blossoms are only produced every second year. The flowers are light pink in color and consist of five petals that measure between 3 and 6 cm (1-2½ inches) in length.
Ariocarpus trigonus is a succulent plant that requires porous soil with good drainage and very little fertilizer. It needs plenty of water (up to 8L per plant) in order not to lose its leaves or branches, which can easily fall off during the hottest parts of summer if there is no rain.
The temperature should be kept at 15-20°C (59-68°F), with a minimum winter temperature of 5°C (41°F). During the winter months, Ariocarpus trigonus requires complete darkness. It is in partial sunlight that the leaves will turn yellow or brown, and a layer of organic mulch will protect them from excessive heat.
In the summertime, it can survive at temperatures as high as 40°C (104°F) for short periods of time, and a minimum temperature of 10°C (50°F) is preferable. Ensure that the pot has good drainage holes when you water Ariocarpus trigonus, because even if it lives in a dry desert environment, it will not tolerate standing water.
How to propagate Ariocarpus trigonus
Ariocarpus trigonus is propagated by taking cuttings from the growth points of branches. The cuttings should be at least 25 cm (10 inches) long and have between one to three leaves on top of the cut end.
Take a cutting in autumn, when it is starting to dry out; this will increase its chances of survival. Another method of propagation is to cut a branch with its roots and pot it separately. You can also plant seedlings in the right environment, but they are delicate and have only a 50% chance of survival. If you want to grow Ariocarpus trigonus from seeds, keep them at 20°C (68°F) during their first year until they germinate.
If you want to take a cutting, prune the plant in mid-summer. For best results, remove the leaves and just expose the stem. Cut off some of it if necessary so that you have between 25 cm (10 inches) and 50 cm (20 inches) of the bare stems remaining.
Put these cuttings into warm water (no soap or fertilizer) for 12 hours, then plant them in the soil. These cuttings can be kept for six months until you are ready to transplant them, but remember that if they dry out even slightly, the roots will die.
Make sure that you don’t seal any of the leaves in the wrapping material when you take a cutting. If necessary, cut off the leaves at the bottom of the stems, but leave a bit of stem above where you removed them in order to provide nutrients to the cutting for as long as possible.
The rate of success when taking cuttings is only 30%, and even if you do get a viable cutting, it will take at least two years for it to reach maturity.
General care information
Ariocarpus trigonus is sensitive to excessive light (during the hottest parts of the year) and heat, a common cause of leaf loss. It will survive short periods at higher temperatures as long as it has sufficient light and drainage; however, it is advisable to avoid these conditions as much as possible.
Ariocarpus trigonus needs a minimum temperature of 5°C (41°F) during winter and 15-20 °C (59-68 °F) during the rest of the year. It will survive higher temperatures and can even withstand brief exposure to 40°C (104°F).
Ariocarpus trigonus lives in soil that lacks nutrients and is always dry, so it needs porous soil with good drainage but doesn’t need any fertilizer.
The ideal pH for Ariocarpus trigonus is between 6 and 7, but it will tolerate a range of 4-8. This means that it can live in soil with or without lime.
To avoid leaf loss, you should water regularly (but not too much) in summer, and only water sparingly during winter.
Ariocarpus trigonus does not need any fertilizer. If you do decide to fertilize it, use only liquid or weak solutions. Do not use any solid forms of fertilizers because they can lead to leaching of the soil around the plant and cause root damage.
Pruning and shaping
Pruning is not usually required. Nevertheless, with time it may be necessary to adjust a specimen or remove dead parts if they decay and risk harming the plant.
Some growers prune for shape; others prefer to let them grow naturally if possible.
A quick tip: Immediately after growth begins in spring, cut about a third of the oldest stems to the ground. This will produce new shoots which make a denser, more attractive rosette.
Repotting is generally not required, at least in the small size pots traditionally used. But they do need fresh potting mix every year or two as it breaks down and stops wetting evenly to keep the roots from drying out.
Pests and diseases
Aphids are a common problem for all succulents, and Ariocarpus trigonus is particularly susceptible to them when it is small. Another common problem for Ariocarpus trigonus is spider mites. These can be easily controlled with a drop of insecticidal soap into the soil every week or so.