Q. Can I grow cacti outdoors in the northeast of the US?
Although cacti (family Cactaceae) are, in general, plants for warm, dry climates, there are species that can be grown in colder regions, as long as excellent drainage and abundant sun exposure are available:
- Opuntia or prickly pear cactus - a large family of cacti with many species that are cold-hardy. The most commonly grown one is O. humifusa (Eastern prickly pear) which is native to the Eastern United States and can be seen in the NYBG's Native Plant and Rock Gardens. O. fragilis, despite its name, is the hardiest Opuntia and can survive to -35º F. It is also found in NYBG's Rock Garden. Many species, e.g. O. polycantha, produce beautiful flowers. The fruits of prickly pear cacti are edible.
- Cylindropuntia or cholla cactus - similar to the prickly pear cactus but with cylindrical stems. This often tree-like genus of cacti includes a number of species that tolerate cold to at least -10º F., including Cylindropuntia imbricata (tree cholla) which is grown in NYBG's Rock Garden and C. whipplei (Whipple's cactus).
- Echinocereus or hedgehog or porcupine cactus - most species are quite small but grow into low, spreading mounds. E. triglochidiatus is known as claret cup or king cup cactus. The species blooms with profuse red-orange flowers while it's many varieties produce a range of colorful flowers. It is hardy to about -10º F and can be seen in the NYBG Rock Garden.
- Escobaria vivipara or spinystar, viviparis foxtail or beehive cactus - a low-growing, round, spiny cactus reaching about 5 inches tall that blooms deep pink-purple and is hardy to -10º F. and often beyond.
- Grusonia clavata (syn. Optunia clavata and Corynopuntia clavata) or club cholla - a low-growing, creeping cactus that slowly forms a mass and is hardy to -25ºF.
Cacti should be grown in a sunny location replicating their native environment. They also need good drainage. Rock gardens or sunny walls are ideal locations for cacti. If you are growing cactus in a wet climate or in clay soil then add plentiful sand and grit to the top layer of soil. They will need nutritional supplements in the form of a weak solution, organic fertilizer when grown in the Northeast.
An excellent article on hardy cacti can be found at http://www.bbg.org/gardening/article/hardy_cacti.
Courtesy of the NYBG Plant Information Service