Publication: Cactaceae (Backeberg) 5: 2809. 1961
Description
Usually solitary the Thelocactus bicolor var. pottsii is one of most beautiful Thelocactus. Unfortunately this plant is supplied only, rarely, sometimes by the name Thelocactus heterochromus.
Stem: Large, globular, low-growing, green, reach hardly 15 cm in diameter and get 10-15 cm tall. Epidermis - bluish-sulphur- green that became almost red-brown during the winter rest when the plants are dry.
Tubercles: Rounded that form 8-11 (usually 9) distinct ribs.
Areoles: Round, on the outer side of tubercle bear semicircular heavy cut.
Spines: 7-11 (-19), powerful, very different in length, thickness and colour.
Central spines: 1-2 (or more) bent back and newly bent to the body the upper one is flattened, red- white colored, the spines produced in spring are brighter and redder while the one produced the hot period of year are paler, some plants have very short spines, whose central prickle has a length of only of 1,5 cm, but there are plants with 5,5 cm long spines. The name “heterochromus” (= many-colored) indicates patch effect of prickles, but it can be also applied to the variable colours of spines in different plants.
Radial spines: 9-11 (-18) 1,5-3 cm long, yellowish strong, awl-shaped, usually bent downward.
Flowers: Imposing 8-10 cm in diameter pink-violet lobes with a dark red throat and yellowish orange anthers.
Blooming season: Flowers appear exclusively from June through August.
Origin and Habitat
Northeastern Mexico (Chiuaua and coahuila) Like many cactus forms of this dry, hot region of Mexico, plants are strongly variable; therefore a precise description is impossible.
Cultivation and Propagation
Thelocactus bicolor is a summer grower species easy to cultivate, more cold tolerant than most and less fussy regarding soil conditions.
Growth rate: It is a relatively rapidly growing and easily flowering species that will make clumps given the best conditions.
Soils: It likes very porous standard cactus mix soil, but can become too elongated if compost is too rich.
Repotting: Use pot with good drainage.
Watering: Water regularly from Spring to Autumn, but do not overwater(Rot prone), keep dry in winter.
Fertilization: Feed with a high potassium fertilizer in summer.
Hardiness: Reputedly somewhat resistant to frost if kept on the dry side prior to, and during, cold weather (hardy to -7 C ° C, or less for short periods).
Exposition: Requires full sun or light shade and careful watering to keep plant compact with strong coloured spines. Tends to bronze in strong light, which encourages flowering and heavy spine production.
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 a variety of insects, 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. Nonetheless, there are several pests to watch for:
- Red spiders: Red sopiders may be effectively rubbed up by watering the infested plants from above.
- Mealy bugs: Mealy bugs occasionally develop aerial into the new growth among the wool with disfiguring results, but the worst types develop underground on the roots and are invisible except by their effects.
- Sciara Flies: Sciara flies are one of the major problems for seedlings. It is a good practice to mulch your seedlings with a layer of grit, which will strongly discourage the flies.
- Scales: Scales are rarely a problem.
It is wise to treat your whole collection with a systemic insecticide twice a year in spring and autumn.
- Rot: Rot is only a minor problem with cacti if the plants are watered and “aired” correctly. If they are not, fungicides won’t help all that much.
Propagation: From seed, since the plant rarely produces plantlets. 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!
Bibliography
Major references and further lectures
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Edward F. Anderson “The Cactus Family” Timber Press, 2001
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Curt Backeberg “Cactus Lexicon” Sterling Publishing Company, Incorporated, 1978
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David Hunt, Nigel Taylor “The New Cactus Lexicon” DH Books, 2006 ISBN 0953813444, 9780953813445
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James Cullen, Sabina G. Knees, H. Suzanne Cubey “The European Garden Flora Flowering Plants: A Manual for the Identification of Plants Cultivated in Europe, Both Out-of-Doors and Under Glass” Cambridge University Press, 11/Aug./2011
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