Mexican Fencepost
Pachycereus marginatus
A columnar cactus traditionally used as a living fence, turning a dramatic purple when cold weather arrives.
Frost sensitive, hardy to about 28°F, USDA 9-11; a low-desert plant needing frost protection in cold pockets.
AMWUA Notes
Drought tolerant columnar cactus that forms a water-thrifty living fence.
Care Guide
Water established plants monthly in summer only and keep dry in winter; sharp drainage prevents rot.
Remove damaged columns; individual stems can be cut and re-rooted to extend the living fence.
Light spring feeding optional.
Generally trouble-free; watch for scale and mealybugs between the ribs.
Stems flush purple in cold weather; protect from hard frost below 28°F.
Soil, Feeding & Propagation
Gritty, fast-draining mineral soil or decomposed granite; low organic matter
Needs sharp, fast-draining soil.
Low feeder.
Stem cuttings re-rooted to extend the living fence
1-2 ft apart in a row for a fence; 5 ft as a clump
Shallow, non-invasive roots; nearly spineless columns are relatively path-safe
Placement Tips
- •Plant columns in a tight row for a living fence or screen.
- •Nearly spineless, so relatively safe near seating.
- •Give room for the 5 ft cluster.
- •Site in fast-draining soil.
Features
Best Uses
Companion Plants
Quick Stats
Design Styles
Include in Your Project
Love Mexican Fencepost? Our landscape team sources from wholesale nurseries and can incorporate it into your design.
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Use this care guide to maintain your Mexican Fencepost. Questions about your landscape? Reach out anytime.
Data from 2024 AMWUA “Landscape Plants for the Arizona Desert” guide.
Mexican Fencepost — common questions
Answers for low-desert Phoenix conditions, drawn from this plant’s growing data.
How much water does Mexican Fencepost need in Phoenix?
Mexican Fencepost is a low-water cactus once established. Water established plants monthly in summer only and keep dry in winter; sharp drainage prevents rot. Drought tolerant columnar cactus that forms a water-thrifty living fence.
How big does Mexican Fencepost get?
Expect roughly 4 ft tall and 5 ft wide at maturity, with a slow growth rate. Allow about 1-2 ft apart in a row for a fence; 5 ft as a clump of spacing when planting. Shallow, non-invasive roots; nearly spineless columns are relatively path-safe.
Can you plant Mexican Fencepost near a pool?
Not ideally. Mexican Fencepost is not rated pool-friendly, so it is better placed away from the pool deck and skimmer. Litter is rated low.
Can Mexican Fencepost handle Arizona heat and winter frost?
Mexican Fencepost is hardy in USDA 9-11 and wants full sun. Frost sensitive, hardy to about 28°F, USDA 9-11; a low-desert plant needing frost protection in cold pockets. Stems flush purple in cold weather; protect from hard frost below 28°F.
Does Mexican Fencepost have thorns?
Yes — Mexican Fencepost has small thorns. Site it back from walkways, seating and pool decks where people brush past.
Is Mexican Fencepost safe around pets?
Mexican Fencepost is listed as pet-friendly in this guide. If your dog is a determined chewer, check any new plant with your vet before planting.
When does Mexican Fencepost bloom in Arizona?
Mexican Fencepost blooms in spring, with yellow flowers.
How much maintenance does Mexican Fencepost need?
Mexican Fencepost is low-maintenance. Leaf, flower and pod litter is rated low. Remove damaged columns; individual stems can be cut and re-rooted to extend the living fence.
What kind of soil does Mexican Fencepost need?
Gritty, fast-draining mineral soil or decomposed granite; low organic matter. Nutrient needs are low. Light spring feeding optional.
Is Mexican Fencepost native to Arizona?
No. Mexican Fencepost is not an Arizona native; it originates from the Central and Southern Mexico, but it is grown successfully in low-desert landscapes here.