Pediocactus simpsonii
| Light | Full sun; bright, airy conditions all year |
|---|---|
| Water | Sparingly in spring and autumn; kept bone-dry and cold through winter |
| Soil | Very lean, fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Extremely cold-hardy; tolerates hard frost and deep snow when dry (roughly USDA zones 4–8) |
| Propagation | Seed (primary); occasionally offsets from clustered plants |
| Toxicity | Non-toxic to cats and dogs |
Pediocactus simpsonii is a widespread, exceptionally cold-hardy montane cactus of the Rocky Mountains and Great Basin of western North America. It forms a low, rounded body that spends much of the year shrunken level with the ground, then swells up and rises to bloom in the very early spring, often while snow still lingers nearby. It is commonly known as the mountain ball cactus or Simpson's hedgehog cactus.
Description
Pediocactus simpsonii is usually a solitary globe, though older plants may cluster into small mounds. Individual heads are typically 5–15 cm across and low-domed, the surface arranged into spiralling tubercles rather than sharp continuous ribs. Each tubercle carries a densely spined areole: a spreading outer ring of pale radial spines surrounding a few darker, stouter central spines, the colour ranging from whitish through reddish-brown depending on the population.
Flowers open at the crown in early spring, well ahead of most other cacti, in shades of pink, magenta, yellowish or greenish-white according to the plant. They are relatively small and funnel-shaped, clustered near the growing point. A distinctive feature of the species is its seasonal contraction: as the soil dries and cold sets in, the plant draws down into its rootstock and the ground, so that in winter little more than a spiny disc may be visible at the surface.
Distribution and habitat
The species has one of the broadest ranges and widest ecological tolerances of any Pediocactus, scattered through the mountains and high basins of the western United States — across the Great Basin, the Rockies and adjacent ranges, from relatively low sagebrush flats up into montane pine and grassland at considerable elevation. It grows in gritty, well-drained soils among rocks, grasses and low shrubs, where it endures fierce sun, drying wind, and long, cold winters with snow cover.
This wide distribution and variable appearance mean the species has been divided into several varieties by different authors, and its taxonomy has been revised many times. Because it experiences a genuine cold, dry dormancy in habitat, it is one of the hardiest cacti in the world.
Cultivation
Pediocactus simpsonii has a reputation as a challenging plant in cultivation, quite unlike its toughness in the wild. The key is to respect its natural rhythm: a very lean, sharply draining, mostly mineral mix, full sun, excellent airflow, and above all a completely dry, cold winter rest. Water is given only during the active growth periods of spring and autumn, and even then modestly; the plant is highly intolerant of summer heat combined with moisture, which quickly causes rot.
Many growers find it does best kept cool and airy rather than coddled in a warm greenhouse, and it is a favourite among enthusiasts of hardy cacti who grow it in raised sand beds, troughs or unheated frames where winter cold and dryness come naturally. Grafting onto a hardier or more forgiving rootstock is sometimes used to grow plants on more reliably, though many purists prefer them on their own roots. See Watering, Repotting and Grafting for general technique.
Propagation
Seed is the standard and most reliable method. Like many cold-climate cacti, the seed benefits from a period of cold, moist stratification to break dormancy before it will germinate well, mimicking a winter spent in the ground. Germination can be slow and uneven, and seedlings are small and delicate at first, so patience is essential. Clustered plants occasionally offer offsets that can be removed, but vegetative propagation is uncommon. See Propagation — seed and Propagation — offsets for fuller walkthroughs.
Common problems
- Rot — by far the commonest cause of loss, almost always from moisture during warm weather or any dampness during the winter rest; the plant softens and collapses, often from below.
- Loss of the dormancy cue — kept too warm, wet or shaded, plants sulk, fail to contract properly and are far more prone to disease.
- Pests — mealybugs (white fluff among the spines and roots) and red spider mites can trouble plants grown under glass; root mealybugs are a particular risk in dry mineral composts.
See also
- Pediocactus — the genus overview
- Soil and potting mix · Watering · Repotting · Grafting
- Propagation — seed · Propagation — offsets · Pests and diseases