Pediocactus
Pediocactus is a small genus of tiny, cold-hardy cacti native to the high plains, deserts and mountains of the western United States. Often called pincushion cacti, these diminutive plants are geophytes: through the heat of summer and the cold of winter they shrink down and retract into the soil, all but vanishing until conditions are right. They are treasured by specialist growers and, in the same breath, notorious for being some of the most difficult cacti to keep alive on their own roots.
Description
Pediocactus species are small — most are solitary globes or short cylinders only a few centimetres across, occasionally clustering with age. The ribs are broken up into distinct spirally arranged tubercles, each tipped with an areole bearing a neat cluster of spines that can be stiff and radiating or, in some species, soft and comb-like. Overall the plants read as little spined buttons sitting close to the ground.
Their most distinctive habit is seasonal retraction. As drought or cold sets in, the fleshy body loses water and pulls down into its thick, contractile taproot, drawing the crown level with or below the soil surface where it is protected by grit and debris. In this dormant state a plant can be nearly impossible to spot in habitat. Flowers appear briefly in the growing season — often in early spring as the snow retreats — in shades of white, pink, yellow or magenta, opening at the crown and followed by small dryish fruit.
Distribution and habitat
The genus is entirely North American, ranging across the western United States from the Great Basin and Colorado Plateau into the northern Rockies and adjacent high plains. Species grow in harsh, exposed settings: cold desert flats, gravelly steppe, pinyon-juniper woodland and rocky mountain slopes, frequently on specialised soils derived from a particular rock or clay.
These are among the most cold-hardy of all cacti, enduring hard frosts, snow cover and a genuinely dry, freezing winter dormancy. Many species have very restricted ranges tied to specific soils, which makes them vulnerable; several are protected as threatened or endangered, and — like the whole cactus family — the genus is listed under CITES. Nursery-propagated, seed-grown plants are the only appropriate source for collectors, and wild collecting is both illegal and ecologically damaging.
Notable species
- Pediocactus simpsonii — the snowball cactus or mountain ball cactus, the most widespread and generally the most forgiving species in cultivation.
- Pediocactus knowltonii — a very small, rare species with soft, fine spines, restricted to a tiny range and legally protected.
- Pediocactus paradinei — noted for its long, hair-like spines that veil the body.
- Pediocactus peeblesianus — a diminutive, highly localised species prized (and protected) for its scarcity.
- Pediocactus bradyi — a miniature endangered species from restricted habitats in Arizona.
Cultivation
Pediocactus has a hard-earned reputation as a connoisseur's genus. The chief difficulties are that the plants demand a genuinely dry, cold winter rest and resent both summer heat with moisture and any hint of stagnation at the root. Grow them in a very lean, sharply draining, mostly mineral mix with generous grit, in a deep pot that accommodates the contractile taproot, and give bright light with excellent airflow.
Watering must respect the plant's natural rhythm: water mainly in spring and autumn when the plant is in active growth and swollen up out of the soil, and keep it bone dry through both the winter freeze and the peak of summer, when many species go dormant and pull down. Overwatering — especially in warm, still conditions — quickly causes rot, and losses are common even for experienced growers. Because own-root plants are so touchy, many collectors graft their Pediocactus onto a hardier, faster rootstock; this makes them far easier to grow and flower, though grafted plants lose the natural retracting habit. See Watering and Repotting for general technique.
Propagation
Seed is the standard and usually the only practical method, since these plants rarely offset. Germination can be slow and erratic: many growers give the seed a cold, moist stratification to mimic winter before sowing on a mineral surface, and seedlings are grown on carefully — or grafted early to speed them past their vulnerable first years. Vegetative increase is otherwise limited to grafting the occasional offset or pup. See Propagation — seed and Grafting for details.
See also
- Cactaceae — the cactus family
- Grafting · Soil and potting mix · Watering · Propagation — seed · Repotting · Pests and diseases
- CITES — conservation and trade status