Pachycereus marginatus

Botanical Name — Pachycereus marginatus

Common Name — Mexican Fencepost cactus, Organ cactus

Plant Family — Cactaceae

Background

The Pachycereus marginatus is native to Central Mexico but has been naturalized all throughout Mexico. The columnar trunks can grow up to 20 feet tall and produce short, rounded stems that resemble a pipe organ which is one of the common names. Fence post cactus is the most commonly used name for this cactus and is derived from Mexico where it is used to construct living fences, mainly along roadways.

Growth Requirements

Sun

Pachycereus marginatus 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.

Temperature/ Humidity

These cacti thrive in warm temperatures and low humidity. They will thrive in temperatures above 70 ºF.
They are cold intolerant, hardy to 25 ºF, though it is advisable to bring them indoors once night time temperatures consistently fall below 40 ºF.

Water

Fence post cactus 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.

Soil/Roots

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.

Flowering

Flowers are large pinkish-red and will bloom in Spring. Following the bloom, it develops spiny, yellowish- red fruit.

Fertilization

Pachycereus marginatus 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.

Propagation

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.

Health

Diseases

These cacti are not especially prone to pests. Root rot or fungal diseases can easily occur if the plant is overwatered

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.

Toxicity