Description
Koh-yo (koo-yo or kôyo) is an odd Japanese variety with colourful bodies that take its name from the colours of the leaves in autumn. The old part of the stem is green, but new growth is bright yellow and red with a wide range of intermediate colours. This cultivar is not a variegate because the yellow and red colouring is not permanent, but occurs prevalently on the new growth near the stem tip and along the ribs, but gradually turn to dark green. The colouring accentuates during winter dormancy and is greatly influenced by cool temperature. In spring-summer the bright coloured areas fade and the plant takes a more uniform green appearance. The colouring not only varies during the year, but each individual plant has its own unique particular colouration.
Crested form: The crested form Astrophytum myriostigma cv. Koh-yo f. cristata - despite to its beauty - is still very rare and sought after by collectors, for its unique features.
Stem: Fan shaped. The stems is smooth lacking or mostly lacking white flecks and can be 5-10 cm thick.
Spines: None.
Ribs: Acute.
Flowers: 5 cm in length, pale-yellow, silk-shining unlike the white-spotted plant, occasionally with an orange gloom.
Blooming season: Spring or early summer, They take up to 6 years to bloom.
Fruits: Dry, dehisces towards the apex forming about 5 star shaped lobes. With few seeds.
Origin and Habitat
Japan, Garden origin (Nursery produced cultivar)
Cultivation and Propagation
Variegated and coloured cacti are regarded as choice and difficult in cultivation, but despite that the Astrophytum myriostigma cv. Koh-yo are relatively easy to grow. They are sometime seen as grafted plants, but grow well on their own roots too.
Exposure: They cannot tolerate prolonged exposure to direct sun light (especially during the hottest summer days), so grow them in half-shade or under filtered sun.
Spoil: Use mineral well-permeable substratum with little organic matter (peat, humus).
Watering: Water sparingly from March till October and keep perfectly dry in winter at temperatures from 5 to 15 degrees centigrade. (In general these plants are more tender and cannot endure freezing temperatures ) In the rest period no high atmospheric humidity!!
Crested growth: Unlike ‘monstrose’ varieties of plants, where the variation from normal growth is due to genetic mutation, crested growth can occur on normal plants. Sometimes it’s due to variances in light intensity, or damage, but generally the causes are unknown. A crested plant may have some areas growing normally, and a cresting plant that looks like a brain, may revert to normal growth for no apparent reason. If you have any of the crested part left you need to remove the normal growth and leave the crested part behind this will need to be done regularly.
Propagation: Grafting or cuttings. Plants are usually grafted onto column-shaped cacti but proved to be able to produce their own roots if degrafted. Cuttings will take root in a minimum temperature of 20° C (but better in hot weather). Cuttings of healthy shoots can be taken in the spring and summer. Cut the stem with a sharp, sterile knife, leave the cutting in a warm, dry place for a week or weeks (depending on how thick the cutting is) until a callus forms over the wound. Once the callus forms, the cutting may be inserted in a container filled with firmed cactus potting mix topped with a surface layer of coarse grit. They should be placed in the coarse grit only; this prevents the cut end from becoming too wet and allows the roots to penetrate the rich compost underneath. The cuttings should root in 2 to 6 weeks. Large crested piece must be placed on the soil surface without burying the plant base down in the soil.