If you love cacti, then you’ll love the Mexican fence post (Pachycereus marginatus) cactus. Its descriptive name conjures up images of the desert, fenced-in cattle fields, and the beautiful country of Mexico. But, what exactly is the Mexican fence post cactus? Here’s the Mexican fence post cactus description!
can be a focal point in any arid landscape.
Here is the Mexican fence post
cactus description.
Photo by Doug Martin
Mexican fence post cactus description
It’s a columnar cactus with multiple columns
Just as the “fence post” name implies, the Mexican fence post is a columnar cactus that grows vertically out of the ground. Unlike many columnar cacti varieties, the Mexican fence post does not develop arms, Instead, new pups emerge from the soil and form an underground clump.
Focal point in your landscape
The new pups grow straight up beside its parent. Over time, the tall, vertical columns can make an effective barrier, privacy fence, or a striking architectural statement in your landscape.
When I browse the homes for sale in Palm Springs, California, I often see the Mexican fence post cactus used in the landscape.
This cactus goes well with mid-century modern design
Often, I see them planted in straight lines in front of a beautiful, mid-century modern home. Or, they might be lined up along a sidewalk for a very simplistic, but stunning and welcoming effect.
Growth rate and height
—This cactus can grow fast
The Mexican fence post cactus can grow very fast, especially if you give it supplemental water. Years ago, I bought a 1-foot tall specimen and planted it in a large container. In only two years, it had added almost 3-feet to its height.
Eventually, I had to take it out of its container and plant it in the landscape. This cactus had almost reached the eaves of my overhanging roof.
cactus had almost reached the eaves
of my roof, so I had to move it.
Photo by Doug Martin
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Previously, I had watered deeply once a week when it was in a container. Normally, that would be too much water for many cacti varieties, but my Mexican fence post seems able to handle it well.
Based on my experience, however, it’s best not to give any cactus too much water.
—Height: 12-to-20 feet
Your Mexican fence post should reach 12-to-20 feet in height as it matures. But remember, each column that you plant will produce pups or offshoots.
Those new offshoots emerge from the ground, and then grow quickly. It’s no wonder that the Mexican fence post cactus can make such a dynamic statement in a landscape.
—Column width: 3-to-5 inches thick
Typical widths for a column or trunk of this cactus is about 3-to-5 inches. Some columns might even be a little thicker.
—Total plant width: 1-to-2 feet wide
As this cactus produces pups around its base, the plant width will expand. As the pups grow and their columns thicken, and as they continue to produce more pups, the total plant width could expand to 1-to-2 feet wide or more!
of the Mexican fence post cactus.
Photo by Doug Martin
Short spines that vary in color
The spines on the Mexican fence post are small. Typically, they will be about 3/8-of-an-inch long or less. Old-growth spines are white or beige in color, but the new-growth spines are a beautiful red.
To me, the vibrant red on the new spines makes it look like they’re soaked with blood. Fortunately, however, the short spines on this cactus are relatively safe, especially when you compare it with other cactus varieties. For instance, the toothpick cactus has extremely long spines, and can be very dangerous.
Because the spines are so short, they might be safe to plant near your pool, close to a sidewalk, or right in the middle of your outdoor living area.
of the Mexican fence post cactus.
Photo by Doug Martin
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Drought tolerant
—Tolerates low water amounts
Just like most cacti, the Mexican fence post is drought tolerant and can take the desert heat. Its ability to survive with low amounts of water and high quantities of heat makes this a perfect, low maintenance plant for a xeriscape or container.
—Also tolerates moderate over-watering
Ironically, I’ve found that by giving this cactus variety a little extra water, it will grow very fast. While I am reluctant to give my landscape cacti weekly drinks of water, my Mexican fence post cactus seems okay with the extra moisture. In fact, it seems to thrive.
However, as the days get shorter and cooler, you should cut back to watering this cactus to only once-or-twice a month. Too much water when it goes dormant in the winter can cause any cactus to rot.
To prevent excess water retention around the roots, be sure the soil drains well.
Requires well-draining soil
Many areas of the United States, especially in the southwest, have soils that do not drain well. Here in southern Arizona, the soil has lots of clay that prevents good water drainage.
If you have soil that retains too much water, it’s easy to add soil amendments. Use an equal amount of sand (decomposed granite, shale, river sand, or lava sand) and organic garden soil. Combined with sand, the organic garden soil will open up clay soils, provide better aeration, and add vital nutrients.
Hardy down to 25 degrees F
The Mexican fence post cactus is hardy down to 20-or-25 degrees Fahrenheit. If you occasionally see temperatures dip lower or are expecting an extra-cold night, provide additional protection.
Typically, this cactus will be hardy throughout the year in the USDA hardiness zones of 9a-to-9b up to 11.
Loves the sun but tolerates the shade
In my experience, the Mexican fence post cactus loves the sun and the heat. Even better, it tolerates shade and dappled sunlight. In fact, my fastest growing Mexican fence post is in the shade most of the day.
However, I’ve also found that this variety of cactus also does well in afternoon shade, especially if you live in climates that get extremely hot in the summer.
—Protect from sun during first year
During the first year in your landscape, this cactus will do best if you protect it from the harsh UV rays of the sun. Yellow skin and brown scars indicate that this cactus is getting too much sun. Of course, too much sun is common in the southwestern United States.
One way to protect your new Mexican fence post is to strategically place your outdoor furniture or other plant containers nearby to provide shade. Or, you can use shade cloth with different mesh densities. I think the 40% mesh works well with cactus plants.
was damaged by the sun shortly
after planting. To prevent sun damage,
protect with afternoon shade.
Photo by Doug Martin
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Flowers
In the spring, the Mexican fence post cactus produces pretty pastel white, salmon, and pink tinged flowers on its ribs. After the blooms, you’ll get vibrant red, sweet-tasting fruit.
However, unlike the relatively benign and small spines on this cactus, its fruits have longer and more dangerous spines. The sweet fruit, though, makes the risk of a spine-prick worthwhile.
Landscape uses
The Mexican fence post cactus makes a vertical, striking statement in any landscape. You might use it as a backdrop for other smaller drought-tolerant plants in the foreground.
Or, use it as a privacy hedge. As the years go by, your living fence post will grow new pups and fill in any spaces with a dramatic flair.
Use them to define an outdoor living area, and even to provide a sense of seclusion in your outdoor space. In Palm Springs, California, I’ve seen beautiful examples of Mexican fence posts lined up against a house where they provide a hard-to-resist architectural statement.
—Grow this cactus in a large container
I’ve had great success growing the Mexican fence post cactus in a container. If you grow one in a pot, be sure it is large enough and heavy enough that it won’t tip over and the plant grows.
My container-bound cactus grew quickly—it grew tall, and produced lots of pups all around the base. They also grew very fast. In fast, after five years in the container, I had to move them to my outside landscape, because they got too big!
in any arid landscape. Here it is in front
of a soaptree yucca with a
bougainvillea in the background.
Photo by Doug Martin
Why I love the Mexican fence post cactus, description and benefits
It’s for all those reasons that I love my Mexican fence post cactus. As the years go by, I will propagate more of this columnar cactus with cuttings.
Thankfully, this is a drought-tolerant cactus that requires very little maintenance. In fact, you could go on a long, six-month vacation, and your healthy Mexican fence post cactus will be right there to greet you when you return. It’s just one of those perfect plants to include in your landscape.
TAKEAWAYS:
Mexican fence post cactus description
The Mexican fence post cactus (Pachycereus marginatus) is a tall, columnar plant. It grows pups around its base, so eventually, the plant can be 1-or-2 feet wide.
In the spring, it produces pretty flowers when mature. Afterwards, the juicy red fruit is surrounded by long spines, but the fruit is very sweet.
This cactus is drought-tolerant as well as being heat-tolerant. However, if you live in southern Arizona or other region that experiences extremely hot summer temps, this cactus appreciates afternoon shade.
It makes a striking focal point in any arid landscape. And, because of its simplistic but striking appearance, it works well especially in a mid-century modern design.
Thanks for reading our article about the Mexican fence post cactus description. If you have this wonderful cactus in your landscape or container, please share your experiences!
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Content and photos by Doug Martin and The Zen Xeriscape
