About the genus
Aztekium ritteri was discovered in 1929 in the state of Nuevo León in Mexico. For many years it was the only species known until 1991, when a second species, A. hintonii, was discovered, also in Nuevo León. A third, A. valdezii, has since been found in 2011, also in Nuevo León, but is not available legally for cultivation.
Consequently, little is known about the growth rate and cultivation needs of A. valdezii, although they are believed to be similar to those of A. ritteri, which is significantly slower-growing than A. hintonii and is often grafted. Seedlings of A. ritteri on their own roots, however, can, with patience, be grown to flowering size in around seven to ten years. In cultivation, they can start offsetting around the base at around 12 years, and much sooner when grafted, though all three species are generally solitary in habitat. The flowers of A. ritteri are small and white with pale pink tinges around the edges, and plants normally have 9–11 ribs. The flowers of A. valdezii are small, pink with white centres and plants normally have only 5 ribs.
A. hintonii, however, is a more vigorous plant, with 10–18 ribs and a body growing to around 10cm but rarely offsetting, even in cultivation (on its own roots). It can reach flowering size in around seven years and its flowers are a deeper pink with no white.
How to grow them
In their very few and small habitat sites, aztekiums grow on steep north-facing walls in narrow limestone and gypsum valleys, often vertically in crevices with fine clay and little organic material.
In cultivation, therefore, they need a very open and free-draining compost such as sieved John Innes compost, plenty of sharp sand, (preferably) limestone chippings and perhaps some perlite, vermiculite or similar. Some growers omit the John Innes or other organic components.
Aztekiums can then be watered like the rest of the collection, preferably from below with water drawn upwards by capillary action, to avoid water lodging on the plant body. They should be watered again only when completely dry at the roots.
Nutrients can be added to the water occasionally by a general balanced fertiliser including trace elements, and extra magnesium can be added (sparingly) by including some Epsom salts.
Watering can start from early April or even late March whenever a sunny and warm spell is forecast, until late September or early October. After that, they should remain dry all winter and in as dry an atmosphere as possible with good ventilation and perhaps some heating, to avoid humidity when flowering so that the dying flowers can dry off thoroughly and not rot down into the plant body.
Plants should be repotted only when they have stopped growing or have completely filled the pot and should be moved up only one pot size, after gently removing as much as possible of the existing compost.
Propagation is normally by seed-raising, preferably in a heated propagator with the pots enclosed in polythene to ensure consistent moisture at the roots. Any offsets can however be cut off, dried and may re-root with patience. In winter, the plants are usually fine down to freezing or even below if thoroughly dry and in a dry atmosphere.
Text and photos: David Quail
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