Mexican fence post cactus is a stunning columnar cactus that can make a real statement in your yard. Here’s everything you need to know about planting and caring for this Mexican desert native.
Mexican fence post (Lophocereus marginatus) is a particularly attractive columnar cactus that, unlike most others, grows fast. It has multiple dark green columns lined with white rows of spines that are so symmetric they look like stripes.
In the spring, you may notice small, tubular pink flowers pushed out along its spines. They are short-lived and inconspicuous, so it’s easy to miss them.
Unlike some columnar cactus, this does not branch or have arms — it branches at ground level, sending up tall, straight stems. It’s easy to see why it’s called “fence post.” In its native Mexico, it is sometimes used to form a living fence.
Mexican fence post cactus is an extremely undemanding plant. It grows in full or part sun. It requires no pruning and produces no litter. It needs little water and can take intense desert heat, however, it’s borderline cold hardy.
It is deer and rabbit-resistant, and when in bloom, attracts hummingbirds.
Why I Like This Plant
- Stunning cactus can be a focal point of your yard
- Grows fast
- Easy to propagate new plants
- As maintenance-free as a plant can be
Things to Watch Out For
Like most cactus, it can develop root rot with too much water.
It has thorns, although they are relatively small and less hazardous than those of many other cacti.
It’s not terribly cold-tolerant. When the temperature drops below 25℉, the tips of columns can suffer frost damage. So you may need to protect your plant from cold, depending on its microclimate.
These cacti are very easy to propagate, which makes them susceptible to ne’er do wells who think it’s OK to lop off a piece to start their own plant.😠 Unfortunately, I live where this kind of thing happens. If you do, too, you might want to plant this in your backyard rather than your front yard.
Optimal Growing Conditions
If you’re thinking of adding a Mexican fence post to your garden, you need to find a suitable place that will keep your plant healthy and looking good… while minimizing maintenance for you.
Here are the key factors to keep in mind.
Temperature
Mexican fence post should be grown in USDA Hardiness Zones 9 – 11.
While fence post cactus can survive temperatures down to 20℉, when the temperature drops below 25℉, plants can experience frost damage. It’s not unusual to see column tips covered with paper bags, styrofoam cups, knit caps, or even Santa Claus hats in the winter here in Tucson.
Sun Exposure
Mexican fence post can take full sun and even the reflected heat of a hot wall, but will also do well in part shade.
Size and Growth Rate
Fence post cactus is considered a fast-growing cactus. It will get to be about 10 feet tall in 10 years.
A typical mature specimen will reach a size of 15 feet tall by 5 feet wide, but they can grow much larger, so give it plenty of room to grow.
Soil
Mexican fence post is not particular about soil and grows well in any native desert soil, but it must be well-draining, especially if it is near other plants in your yard that get regular irrigation.
It can be grown in large containers. If you plant yours in a pot, make sure it has drainage holes and use specifically formulated cactus soil.
Mexican Fence Post:
The Essentials
| Common Names | Mexican fence post, fence post cactus |
| Scientific Name | Lophocereus marginatus |
| Origin | Chihuahuan Desert |
| Plant Type | Columnar cactus |
| USDA Zones | Zones 9 – 11 |
| Cold Hardiness | To 25℉ |
| Flower Color | Pink |
| Flower Season | Spring |
| Mature Size | 15′ high x 5’ wide |
| Growth Rate | Moderate to fast |
| Sun Tolerance | Full, part, reflected sun |
| Water Needs | Low |
| Pests & Diseases | Root rot |
| Cautions | Moderate spines |
| Wildlife | Attract hummingbirds Deer, rabbit resistant |
How to Plant
To plant Mexican fence post or any other columnar cactus, dig a hole the same depth as the root system and 3 to 5 feet wider.
Amending the soil with compost or soil mix is not recommended.
However, good drainage is critical. If you know your soil is slow-draining, amend with coarse sand or small gravel until you have a loose, well-drained mix.
Carefully remove the plant from the container, put it in the hole, and press the soil to remove any air pockets.
Plant facing in the same direction that it was in the nursery. Surprisingly, cactus can get sunburned! Better nurseries will mark the pot so you know which direction your cactus has been facing.
Planting cactus is serious business — someone can get hurt! If your fence post cactus is of a substantial size, go into this battle prepared.
Helpful tools include tongs and old pieces of carpet or old towels. Wear long sleeves, eye protection, and sturdy, protective gloves. Most garden gloves are no match for our desert plants. I use a thick pair of welder gloves when dealing with cactus.
When to Plant
The best time to plant Mexican fence post is in April or May. Higher temperatures encourage root development.
How to Care for Mexican Fence Post
Whether you’ve recently planted a fence post cactus or have an existing plant in your yard, here’s how to take care of it to keep it healthy and looking its best.
How to Water
You’re probably used to giving plants a good soaking immediately after transplanting, but that isn’t the best practice with cactus.
The Arizona-Sonora Desert Museum advises not to water succulents for one to two weeks after planting.
When your cactus is young, water it once per month during the hot spring and summer, unless you’ve had rains of ½ “ or more. It should not need any irrigation during the winter. Too much water will cause this cactus to rot.
Once it’s established, it should not need any water, unless there is severe drought.
Should You Fertilize?
There is no need to fertilize fence post cactus, they get all the nutrients they need from desert soil. But if you keep it in a pot, fertilize lightly a few times a year when it’s actively growing.
How to Prune and Propagate
Mexican fence posts don’t need pruning unless one of the stems has experienced damage. This can occur from frost, an animal taking a bite, or some human folly.
If you need to remove a stem, you can use that to grow a new plant by simply setting your cutting aside for about one week to let it form a callus. Then stick the hardened end into the soil. That’s all there is to it!
Plant Lover Facts
Mexican fence post cactus have been introduced and naturalized throughout much of Spain and parts of Cambodia.
Mexican fence post cactus has a few other common names including organ cactus, Mexican organ pipe cactus, and Central Mexico organ pipe.
The current accepted scientific name is Lophocereus marginatus, but the most commonly used name is still Pachycereus marginatus.
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Author Bio
Deane Alban is the creator of Southwest Gardener. She is a science writer with a bachelor’s degree in botany from the University of South Florida. Gardening is her lifelong passion. She’s been gardening in Tucson for 15 years.
