Botanical Name — Cleistocactus strausii
Common Name — Silver Torch Cactus
Plant Family — Cactaceae
Cleistocactus strausii are slender columnar cacti known for the white fuzz that covers their trunks. They are native to high mountain regions of Bolivia and Argentina, where they enjoy a sunny desert environment often over 10,000 ft.
- Cleistocactus strausii 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.
- These cacti thrive in low humidity and temperatures above 70 ºF.
- Being from a mountainous climate, they can withstand occasional drops below freezing temperatures as long as they are dry. Their natural environment gets next to no rain in winter. It is advisable to bring them indoors once night time temperatures consistently fall below 50 ºF.
- Cleistocactus strausii 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 overwater. Excessive moisture can quickly lead to root rot.
- During the winter, water one once every two months or so.
- 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.
- Cleistocactus strausii do not flower until they are 10 to 15 years old.
- Narrow, pink, tubular flowers will form in the summer once it has reached a height of at least 3 feet.
- Cleistocactus strausii 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 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.
- Cleistocactus strausii is toxic to humans and animals if eaten. Spines are sharp beneath the fuzzy exterior, so it is advisable to keep out of reach of pets and small children.