Oreocereus celsianus, or the "old man of the Andes" is a columnar, cactus growing in clumps that, in the wild, may reach and exceed 3 m of height (but usually less than 2 m tall). It is difficult to see the shape of the ribbed stem, as it is thickly clothed with silky white hairs.
The stem is thick, erect, cylindrical up 8-12 cm in diameter, covered in a downy white hair, with greatest density at the tips of stems receding to near-bare at the base. The stems branch with time at the base, the new branches are either prostrate or ascending, erect above. Orangish-yellow spikes protrude from around the plant.
It flowers from spring to summer. The diurnal pale purplish pink to dark red tube like flowers appear near the ends of the stems.
Oreocereus cactus need full sun exposures with ample airflow to produce dense hairs, but, as a former mountain dweller, does not care for extremely high temperatures in summer.
Grow it in a rich and particularly draining substratum, as it is very sensitive to rottenness when in presence of humidity and low temperatures and let the soil dry out between waterings.
In summer, during the vegetative period, it must be regularly watered, but allowing the substratum to completely dry up before irrigating again; in winter, it’s to be kept dry. Preferable not to water on overcast days, humid days or cold winter days.
A slow-release fertilizer applied in the spring will be sufficient for the whole year. Repot in the spring, when their roots become cramped. Generally, they should be repotted every other year in order to provide fresh soil. After repotting, do not water for a week or more.
Excellent as landscape or patio plant. It is suitable for small “desert” gardens.
For watering cacti, the golden rule is to make sure the soil is completely dry before watering! This will stop the roots from rotting. It is advised to always use a pot with a drainage hole so that excess water can get drained out. If kept in a sunny area, you will need to water it once every week. If it is in a semi shaded or filtered light area, you might need to water it once in 2 weeks.
Cacti like soil that is well aerated and fast draining. You can fertilise the cactus in the summer months when it is in its growing season. During the winters it is best to cut back on any fertiliser and let the plant rest.