Cereus forbesii
| Light | Full sun to bright light; tolerates some shade |
|---|---|
| Water | Moderate in growth, allowing the mix to dry between waterings; keep dry in winter |
| Soil | Fast-draining mineral or gritty cactus mix (see Soil and potting mix) |
| Temperature | Keep above freezing; USDA zones 9b–11 |
| Propagation | Cuttings (very easy); seed |
| Toxicity | Generally considered non-toxic to cats and dogs |
Cereus forbesii is a fast-growing, columnar cactus from South America, admired for its handsome bluish, waxy stems and easy-going nature. It is grown both as a stately blue column in its own right and, in the popular spiralled Cereus forbesii 'Spiralis form, as a curiosity whose ribs twist elegantly around the stem. Like many members of the genus Cereus it is vigorous, forgiving and well suited to beginners.
Description
Cereus forbesii forms an erect, branching column that can reach several metres tall in the ground, though it stays far smaller in a pot. Young stems carry a beautiful glaucous blue-grey bloom that is strongest on new growth and fades toward green with age and sun exposure. The stems are usually divided into a handful of broad, well-spaced ribs bearing felted areoles and stout spines that vary from pale to dark.
Mature plants produce large nocturnal flowers, white within and tinged with pink or brownish tones outside, opening at night and closing by the following day. These may be followed by fleshy, edible fruit. The much-loved Spiralis form differs only in that its ribs wind in a gentle helix up the stem, giving each column a sculptural, corkscrew appearance; it is otherwise an ordinary, easy Cereus.
Distribution and habitat
The species is native to South America, occurring in Argentina, Bolivia and neighbouring regions, where it grows in warm, seasonally dry scrub and open country. In these habitats it endures strong sun, heat and extended dry spells, retreating into slow growth during the driest part of the year and flushing when rains arrive.
Cultivation
Cereus forbesii is one of the more rewarding and undemanding columnar cacti. Grow it in a free-draining, mostly mineral mix in the brightest position available; strong light keeps growth compact and preserves the blue bloom, while too little light produces thin, pale, etiolated stems. Water generously through the warm growing season once the mix has dried, then keep the plant dry and cool over winter to prevent rot and encourage a natural rest.
The species is frost-tender, so protect it from freezing temperatures. Its vigour and straight, sturdy habit also make it a widely used grafting stock for slower or more delicate cacti. See Watering and Repotting for general technique, and Grafting if you intend to use it as rootstock.
Propagation
Propagation is very easy. Stem cuttings root readily: sever a section, allow the cut end to callus for several days to a couple of weeks in a dry, shaded spot, then set it on a barely moist mineral mix until roots form. Seed is also straightforward and germinates well with warmth and humidity. See Propagation — cuttings and Propagation — seed for full walkthroughs.
Cultivars
The best-known selection is the Spiralis form, prized for the spiral twist of its ribs. It is propagated vegetatively from cuttings to keep the spiralled habit true, since seed-grown plants do not reliably inherit the twist. Care is identical to the ordinary species.
Common problems
- Rot — the usual cause of loss, almost always from overwatering, a poorly draining mix, or wet cold conditions in winter.
- Etiolation — insufficient light produces weak, pale, narrow growth and dulls the attractive blue colouring.
- Corky scarring — sun, wind or handling can leave permanent brown marks on the lower stem; unsightly but not harmful.
- Pests — mealybugs (white fluff in the areoles) and, less often, scale and red spider mites. See Pests and diseases.
See also
- Cereus — the genus overview
- Grafting · Soil and potting mix · Watering · Propagation — cuttings · Propagation — seed