Like so many interesting Euphorbia species, Euphorbia polygona is from the Cape Province of South Africa. It does look a lot like E. horridus, is slow to grow, yet is a sought after plant by collectors. Interesting deep crimson flowers distinguish it from its close relative.
The distinctive ribbed plant grows in a column, a bluey grey with small spines on the ribs.
Over time Euphorbia polygona can grow to reach a height of 1.5m, although this is unusual in cultivation. They do however set offsets and will form a nice colony over time. New growth is green, however it does turn to the wonderful grey over time. In the natural environment the clumps look like little 'Euphorbia cities' an amazing sight.
The main requirement is good drainage, in the UK Euphorbia polygona really needs to be grown indoors. Best is a container with free draining potting mix. They really thrive on neglect and the main problem is over watering, or heavy potting mix.
Good light is essential and watering in winter should be minimal to non at all unless the plant is in a very warm dry environment. A little cooler temperature over winter is important. The plant will respond to an increase in warmth in spring as it puts on new growth.
As with all plants, try to mimic the natural environment and Euphorbia polygona will respond well.