(This plant comes in a 3.5" pot. You will receive a very similar plant to the one in the picture. It may or may not be blooming at the time of your purchase. The plant is shipped in its pot to prevent any damage to the roots).
Description: It is a highly variable densely spined species. Some cluster aggressively and form 30 to 90 cm large clumps that appear white, while other seem to stay more solitary.
During the summer it is best to keep the plants outside where the temperature can rise to over 30°C with no harm to the plant. Furnish good drainage and use a an open and free draining mineral compost that allows therefore roots to breath. They like only a short winter's rest and should be kept almost completely dry during the winter months, If the soil is allowed to be dry for too long root loss could follow but equally the same result would occur if the plants are both wet and cold. From March onwards the plant will begin to grow and watering should be increased gradually until late May when the plant should be in full growth.
Water regularly during the summer so long as the plant pot is allowed to drain and not sit in a tray of water. During hot weather you may need to water the plants more frequently so long as the plant is actively growing. From late September watering should be reduced to force the plant to go in to a state of semi dormancy, by October you should be back in to the winter watering regime.
Propagation: Seeds or stem cuttings from adult plants.
Some of the information in this description has been found at desert-tropicals.com, llifle.com and cactus-art.biz