Echinocactus
Echinocactus is a genus of ribbed, barrel-shaped cacti native to the southern United States and Mexico. Ranging from modest solitary globes to massive barrels well over a metre tall, its members share stout, formidable spines and dense woolly crowns from which the flowers emerge. The genus is best known to hobbyists for the golden barrel, Echinocactus grusonii, one of the most widely grown ornamental cacti in the world. Plants of this genus are among several unrelated cacti loosely called barrel cactus.
Description
Echinocactus species are ribbed, globose-to-barrel-shaped cacti that keep a broadly barrel-shaped silhouette throughout their lives. The body is divided into numerous prominent, sharply defined ribs lined with closely spaced areoles, each carrying a cluster of rigid, often curved or flattened spines. Depending on the species these spines range from pale golden yellow to reddish-brown or nearly black, and in the larger forms they are genuinely fierce.
A defining feature of the genus is the mass of wool that builds up at the crown of a mature plant. Flowers arise from this woolly apex — funnel-shaped blooms in yellow, pink or purplish tones, usually opening only in strong sun — followed by dry, woolly fruit. Growth is slow and steady, and the biggest species may take many decades to reach full size.
The genus has historically been broad and much revised; several plants once placed here have been moved to related genera such as Ferocactus and Kroenleinia. The golden barrel itself is now sometimes treated under the name Kroenleinia grusonii, though it remains universally known in the hobby as an Echinocactus.
Distribution and habitat
The genus is centred on Mexico, with its range extending north into the southwestern United States, particularly Texas, New Mexico and Arizona. Plants inhabit deserts, arid grasslands and rocky hillsides, typically growing in exposed, sun-baked positions in gritty, fast-draining ground.
Several species have suffered in the wild from habitat loss and over-collection. Like the whole cactus family, Echinocactus is listed under CITES Appendix II. Nursery-propagated plants — especially the golden barrel — are abundant, inexpensive and entirely legal to own and trade; wild collection is not.
Notable species
- Echinocactus grusonii — the golden barrel cactus, a rounded green barrel wrapped in brilliant golden spines and topped with white wool; by far the most popular species in cultivation.
- Echinocactus platyacanthus — the giant barrel or biznaga, the largest species, forming huge barrels that in habitat can reach well over a metre tall.
- Echinocactus horizonthalonius — the blue barrel or eagle-claw cactus, a smaller, blue-grey globe with strongly ribbed sides and stout curved spines.
- Echinocactus texensis — the horse crippler, a low, flattened, ground-hugging species of the southern plains, notorious for its heavy central spine.
- Echinocactus polycephalus — the cottontop or many-headed barrel, which clusters into mounds of heavily spined heads in the hottest deserts of the American Southwest.
Cultivation
Echinocactus are rewarding, long-lived plants that reward patience. Grow them in a very free-draining, mostly mineral mix and give them the brightest position you can — full sun suits them and brings out the best spine colour. Water generously during the warm growing season once the mix has dried, then keep plants dry and cool through winter, when they need a proper rest to stay healthy and to flower.
Overwatering and poor drainage are the commonest causes of loss, since a cool, wet root system quickly leads to rot. Most species are surprisingly cold-tolerant if kept bone dry in winter, but few will forgive standing in damp soil. Because these plants grow slowly and eventually become heavy and extremely spiny, plan ahead for repotting: a thick pad of folded newspaper or a length of hose looped around the body makes a spiny barrel far easier to lift. See Watering for general technique.
Propagation
Most Echinocactus are grown from seed, which germinates readily on a warm, gritty surface kept humid until the seedlings establish. Growth from seed is slow but steady, and it is the only practical route for the solitary species. The few clustering species, such as E. polycephalus, can in principle be divided, but offsets are seldom produced freely and seed remains the standard method throughout the genus.
Cultivars and hobby notes
The golden barrel dominates the hobby, and most selection has happened within that species. Growers prize specimens with especially dense, richly coloured golden spines, and a handful of forms circulate, including a short-spined or nearly spineless selection and variegated plants with patches of yellow body colour. Variegates lack full chlorophyll and grow more slowly, so they generally need a little shade from the fiercest midday sun and careful watering. Beyond E. grusonii, the other species are grown more as characterful collector's plants than as named cultivars.
Common problems
- Rot — almost always from overwatering, a slow-draining mix, or winter damp; the barrel softens and discolours, often from the base.
- Corky scarring — cold, wet or scorched patches can leave permanent tan corky marks on the body; unsightly but not usually fatal.
- Pests — mealybugs (white fluff hiding in the wool and between ribs) and red spider mites (fine webbing and a bronzed, dusty skin) are the usual offenders. See Pests and diseases.
See also
- Echinocactus grusonii — the golden barrel cactus
- Ferocactus — the closely related "fishhook" barrel cacti
- Grafting · Soil and potting mix · Watering · Repotting · Propagation — seed