Botanical Name — Cereus forbesii
Common Name — torch cactus
Plant Family — Cactaceae
Cereus forbesii are large, hardy, shrub-like cacti. They are native to South America (Argentina, Bolivia, and Paraguay), where they have adapted to a range of environments. Where they are endemic, they can be found growing in arid plains, forests, atop hills and rocky cliff sides, and along the edges of salt flats. In their native habitat they are widespread and abundant, facing no ecological threats. These fast growers are heavily branched and can reach two meters in height or taller. The generic name Cereus, is derived from a Greek word that translates to “torch” or “candle”.
Cereus forbesii require plenty of full sun. Eight hours of direct sunlight a day is ideal but at a minimum these plants should be provided with at least five hours.
If you are growing them indoors a spot in a south facing window is ideal. If growing these outdoors, place them in an area where they will get light shade to protect them from peak afternoon sun.
These cacti thrive in warm temperatures and low humidity. They will thrive in temperatures above 70 ºF.
They are cold intolerant, hardy to 28 ºF, though it is advisable to bring them indoors once night time temperatures consistently fall below 50 ºF.
Cereus forbesii are extremely drought tolerant. Water them thoroughly, fully saturating the soil. Always allow the soil to dry out completely in between waterings.
If you are unsure whether or not the soil is dry, wait a few days before watering. It is much better to underwater than over water. Excessive moisture can quickly lead to root rot.
These plants prefer a gritty, sharply draining mix. Use cactus soil or amend regular potting mix with sand and fine pumice up to 50% to improve texture and drainage.
In desert climates these plants can be potted directly in the earth and grown outdoors year round.
Large funnel-shaped flowers blossom from late spring to early summer, opening at night and lasting no more than 24 hours. These plants are heavy bloomers. Flowers are typically pinkish-white to red in color.
Cereus forbesii do not require fertilization, however a boost of nutrients during the growing season will help them thrive. Use a fertilizer formulated specifically for cacti and succulents, once a month, during the spring and summer only.
These plants can be reliably propagated from stem cuttings. Use a clean, sharp blade to sever a segment of a stem or an entire branch. Place the cutting in a shaded area for a few days to allow the wound to callous over, then pot in a well-drained cactus mix.
These plants can also be grown from seed. Sow seeds just below the surface, using a well-drained soil mix. Provide a humid microclimate to encourage germination and keep soil evenly moist during the first few months to encourage seedling growth.
These cacti are not especially prone to pests and diseases. Root rot can easily occur if the plant is overwatered. Keep an eye out for common pests such as mealybugs, aphids and scale.
Maintenance (pruning, legginess, repotting)
These hardy plants require very little maintenance. Container grown cacti prefer to be rootbound, so repotting should be necessary only once every two years. Repot into a planter 2” larger in diameter to give the plant plenty of room to continue growing.
Cereus forbesii have no known toxicity to humans or animals. Spines are sharp so it is advisable to keep out of reach of pets and small children.