Copiapoa tenuissima is a geophytic cactus arising from a large tuberose root that can slowly branch from the base to form small clumps. It differs from Copiapoa humilis for its smaller stems, and its taxonomic status is controversial. It is not clear whether it should be treated as a species or as some lower rank.
It is not too difficult in a greenhouse, although grows quite slowly. It is usually seen as a grafted plant but can grow on its own roots too. Soil: Use a mineral well permeable soil with little organic matter (peat, humus). Exposure: They need a good amount of light shade to full sun this help to keep the plants healthy, although slow growth. Watering: Water sparingly from March till October (weekly during summertime, if the weather is sunny enough), with a little fertilizer added. Less or no water during cold winter months, or when night temperatures remain below 10° to prevent root loss. It is sensitive to overwatering (rot prone). Fertilization: Feeding may not be necessary at all if the compost is fresh then, feed in summer only if the plant hasn't been repotted recently. Do not feed the plants from September onwards as this can cause lush growth which can be fatal during the darker cold months. Hardiness: Keep perfectly dry in winter at temperatures from 5 to 15 degrees centigrade. (but it is relatively cold resistant and hardy to -5° C, or possibly colder for short periods) In the rest period no high atmospheric humidity!! (Temperature Zone: USDA 9-11)