About the genus
Thelocactus must be one of the most popular cactus genera in cultivation containing about 22 taxa. They come mainly from Mexico with the widespread species T. bicolor just extending into nearby USA.
The history of the name Thelocactus starts with Schumann in 1898 when the name appeared as a subgenus of Echinocactus in the seventh part of his book Gesamtbeschreibung der Kakteen. It became a genus when Britton and Rose published it in 1922.
There is considerable diversity in the genus, both in spination and flower colour. Plants can be solitary while others make large clusters of stems. Flowers are produced from new areoles in the crown of the plant, some being large and white but there are other species that flower pink and a few have yellow blooms. The main flowering time is in early summer but there can still be flowers produced into September.
The range of spination and body colours gives a specialist collection an attractive appearance even when out of flower.
How to grow them
The brightest situation you can provide will produce the best results for these plants. They are sun-lovers and respond to good light by producing strong spines and many flowers.
An open compost, such as one made from John Innes with added horticultural grit is suitable for all Thelocactus species. These plants are less sensitive to alkalinity than other cactus genera, although they grow equally well in a soil with some organic matter included. When the plants get larger, in a 12cm pot or more, use shallow pots or pans rather than full depth ones.
Plants should be watered freely in summer, ideally with rainwater, including occasional feeding, and then kept completely dry in winter when they just need frost protection.
Most species are available to buy as seeds, which is the best way to add more thelocacti to your collection, and they are easily raised by following the usual methods for cacti. The seeds are large and the young plants grow easily and quite quickly. Plants can be attacked by mealy bugs and are attractive to red spider mite resulting in browning of the plant bodies, particularly near the growing point.
Recommended species are T. conothelos subsp. aurantiacus for its wonderful yellow flowers; T. bicolor for having one of the most beautiful of all cactus flowers; T. hexaedrophorus for its grey-green body and large white flowers; T. macdowellii for its white spines and contrasting pink flowers; and T. rinconensis for its large solitary bodies and flowers in various colours.
For more information, look for a second-hand copy of John Pilbeam’s useful little book Thelocactus, the first in the Cactus File Handbook series published in 1996.
Text and photos: Graham Charles
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