It was first found in Argentina by Castellanos in 1934. Whilst the New Cactus Lexicon considers it as a weakly-spined form of T. alexanderi, there are various clones in cultivation that range from those with almost no spines to ones that have quite pronounced spination, but less than the typical T. alexanderi.
This plant benefits from well-drained compost (e.g. 1 part John Innes to 1 part coarse grit) and is watered from mid-March to end-September (UK climate). At other times, keep it completely dry on a high shelf in your greenhouse. It is slow growing – only one or two new segments each year (and that is if you are lucky!) – and will reward you with flowers in the summer if grown in a very bright position.
In common with some other Opuntias, T. geometricus can suffer from the dreaded ‘black spot’ (black areas on the segments but also within the body) which are believed to be bacterial, and often mean the demise of that segment. Removal of the segment is advised to lessen the spread of disease. As an insurance policy, it is also worthwhile removing the occasional 1-2 year old segment, allowing it to callous over, and then rooting down in a similar compost mix as above.
Other Tephrocacti that are well worth growing are T. articulatus, T. bonnieae and T. molinensis.
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