Think of cacti and images of warm, sunny holidays and balmy deserts come to mind, so it may come as a surprise to learn that a huge range of this family are also astonishingly cold tolerant. In locations from Chile to southern Canada, many cactus species have evolved to shrug off positively Arctic blasts of less than -30C (the UK record low is -27C), and indeed in Britain there are several impressive examples of outdoor cacti.
If you fancy trying a horticultural gamble this summer, you could have your own outdoor cactus garden anywhere in Britain by following these three golden rules…
1) The single most important thing to remember is that in cool climates cacti need perfect drainage. They can be susceptible to rot if left to sit in cold, wet conditions. In the ground this could come in the form of a raised bed filled with a good 45cm of rubble and gravel, essentially just as you would a traditional rock garden. Sitting this on a slope will cause the water to drain off even faster. Alternatively you could pop them in a container, such as unglazed terracotta, filled with gravel, or even plant them into tufa as you would an Alpine. In the Andes cacti are often planted on the top of dry stone walls where they act as a sort of living barbed wire, with the wall giving them the perfect drainage they love. Sitting the cacti in the rain shadow of a house or even under the eaves to keep the worst of the winter rain off will give you an extra edge.
2) As with most plants, hardiness can vary enormously within the individual species. Going for plants from the extreme north or south of the cactus range or from locations with very high altitude will maximise your chances of success. I love the “bunny ears” cactus, Opuntia humifusa, for its bright yellow flowers that smell of citrus. Growing as far north as New York State and southern Canada, it knows how to handle winter lows. More northerly still, there is O fragilis (see picture, above) with large showy flowers in pink or yellow, whose native range reputedly extends almost up to the southern edge of the Arctic Circle. If you prefer ball-shaped species, there’s the adorable Escobaria vivipara (left), whose entire surface is covered in a lace-like network of fine spines. When these erupt into fluorescent fuchsia blooms they take your breath away.
3) The more light you can get cacti under the better. These plants simply won’t tolerate shade in damp, soggy climates, so treat them to the sunniest site you have – ideally against a south-facing wall.
That’s it! Remember these three tips and anyone can be an outdoor cactus grower.
Email James at james.wong@observer.co.uk or follow him on Twitter @Botanygeek
