Publication: Lobivia 85: 144, 116. 1987 [1985-86 publ. 1987]
Description
Rebutia pygmaea var. knizei (Rebutia knizei) is one of the morphological or local forms of the very variable Rebutia pygmaea characterized by yellow or orange-yellow flowers with green stigma lobes. Although R. knizei is very similar to Rebutia diersiana they come from quite faraway sites. The former grows at higher altitudes (3800 m) and also in collections is much rarer. Moreover it has sharper petals and the spines are more dense, otherwise the number of ribs and radial spines is the same, the colour of the flower as well. The stems is dark-green and take a violet tinge on in the sun.
Origin and Habitat
Uyuni to Tupiza, Potosi, Bolivia
Cultivation and Propagation
Rebutia pygmaea var. knizei (Rebutia knizei) is a summer grower species that is easy to cultivate and recommended for beginners. It has has delightful flowers and the plants remain compact, and clumps can easily be managed by division. Another advantage is that the plants are very cold hardy in Winter if kept dry.
Growth rate: It is a slow growing but easily flowering species that will make clumps given the best conditions.
Soils: It likes very porous standard cactus mix soil with a pH slightly on the acidic side.
Repotting: This species will occupy a small flower pot comfortably and remain a manageable sized house plant, repotting should be done every other year or when the it has outgrown its pot. Use pot with good drainage.
Watering: Needs moderate to copious waterings in summer, but do not overwater (the root system is rot prone) and allow the pot to dry out between waterings. Keep dry in winter at a minimum temperature of 0°C.
Fertilization: Feed with a high potassium fertilizer in summer.
Hardiness: It is reputedly resistant to frost if kept on the dry side prior to, and during, cold weather and requires a winter rest period (hardy to -12 C ° C, or less for short periods), but for safe cultivation it is best to avoid freezing temperatures. It does not like high temperatures in summer, and will be perfectly happy in pots outdoors from April to September if protected from torrential rain and hail
Exposition: The plant tolerates extremely bright situations but enjoys filtered sunlight or afternoon shade, inside it needs bright light, and some direct sun. Tends to bronze in strong light, which encourages flowering and heavy spine production, but is likely to suffer from sun scorch or stunted growth if over exposed to direct sunlight during the hottest part of the day in summer.
Uses: It is an excellent plant for container growing. It always looks good and stays small. It look fine in a cold greenhouse and frame or outdoor in a rockery.
Pests & diseases: It may be attractive to and liable to damage by spider mites and thrips but plants in good condition should be nearly pest-free, particularly if they are grown in a mineral potting-mix, with good exposure and ventilation.
Rot: This species is particularly easy and accommodating, seldom suffer of cryptogamic diseases. Rot it is only a minor problem with rebutias if the plants are watered and “aired” correctly. If they are not, fungicides won’t help all that much.
Propagation: Division, direct sow after last frost. Seeds germinate in 7-14 days at 21-27° C in spring, remove gradually the glass cover as soon the plants will be well rooted (ca 1-2 weeks) and keep ventilated, no full sun for young plants! To make a cutting twist off a branch and permit it to dry out a couple of weeks, lay it on the soil and insert the stem end partially into the soil. Try to keep the cutting somewhat upright so that the roots are able to grow downward.
Note: It would appear that in cultivation they grow larger and cluster more vigorously than in habitat.
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