Rainbow Cacti are not injured in zero temperatures out of doors, but with colder weather than this they require some protection. They may be grown in cool, dry, sunny conservatories. The Rainbow is one of the most difficult of the cacti to grow under cultivation. Unless planted in rocky soil, preferably early in spring, it will grow for only a year or two. Young plants transplant more readily than older ones, and neither the roots nor the stems should be injured in digging. Give enough water to keep the soil moist during the growing season. Plants may be grown from seed in moist sandy soil in part shade or diffused sunlight. When mature plants are used and transplanted in early spring they blossom the same season.
RAINBOW CACTUS (Echinocereus rigidissimus)
A popular beauty, named from the brilliantly colored spines arranged around the plant in many-hued bands or “zones.” Called by the Mexicans Cabecita Del Viejo.
Short Spined Strawberry Cactus (Echinocereus Bonkeræ)
(Named for Frances Bonker, one of the authors of this book)
How to identify and how it grows
Bonkeræ, or the Short Spined Strawberry Cactus, is oblong-cylindrical with the tips somewhat depressed. It has low obtuse ridges, fewer than twenty, of a light green. These ridges are covered with a network of radial spines, the younger ones whitish, fading to gray-white, yellow or yellowish brown in age. The centrals are yellow-brown changing to red-brown in older thorns. All the spines are less than a half-inch long and vary in coloring, with brown bulbous bases and translucent tips. This cactus is to be found in clusters of from two to ten stems, and is very attractive with its rose-purple to deep rose-purple flowers nearly three inches long, and its many stamens, stigmas, and filaments in bright and light green. The fourteen petals and nine sepals have obtuse tips and short points; the styles are longer than the stamens. Plants grow along the dry foothills and low mountains in clumps of a foot or less across.
How to grow
This species grows outdoors and is not injured by temperatures twenty or twenty-five degrees below freezing; in colder climates than this it must be given some protection or grown in cool, dry, sunny greenhouses. Plants may be grown at any season in gravelly or sandy clay soils with light irrigation every two or three weeks to moisten the soil during the growing season or in droughty periods. Or they may be grown readily from seed sown in sandy loam in flats or pots, with partial shade and with enough water to keep the soil moist. The species is a handsome one for rock gardens, as yet little known. Mature specimens transplanted early in spring blossom the same season.