Mexican Fence Post Cactus Care - Growing Pachycereus Marginatus

Last Updated on April 14, 2022 by Admin

Mexican Fence Post Cactus are also known as Pachycereus Marginatus. Although, you may see it documented in references as Lophocereus marginatus, which is the plant’s scientific name.

Other names you may here this plant referred to by include Organ Pipe Cactus and Organ Cactus.

The plant gets its name Fence Post Cactus from its shape which makes it ideal to borders or barriers.

It is a native of Mexico and the Southern part of the U.S.

How do your care for the Mexican Fence Post Cactus? Give it full sun and plenty of direct sunlight. It loves this along with hot, dry weather like what you get in the desert.

The plant rarely needs water. So, you don’t need to water it more than once every 2-4 weeks. In winter, only water once every 4-6 weeks. Otherwise, you run the risk of overwatering and root rot.

Table of Contents

Mexican Fence Post Cactus Plant Care

Light Requirements

The Mexican Fence Post Cactus loves sunshine. And it needs at least 6 hours a day minimum of full sun if you keep it outdoors.

Indoors, place it somewhere it can get direct sunlight for the same duration on a daily basis.

In terms of strong, intense, direct sun, this cactus variety is the antithesis of most houseplants. While most indoors plants like medium to bright, indirect sunlight and no direct sun, the Mexican Fence Post Cactus thrives on direct sunlight.

As such, keep it away from curtains or any furniture that may block the rays of the sun.

And place it near a south facing window to soak in as much rays as it can.

Outdoors, avoid any structures, trees or shadows that can case shade on the plant to prevent the sun from reaching it.

If you live in colder regions, you do need to prepare for winters as the days will be shorter and the sun won’t be as bright.

A good solution to this is grow lights. LED grow lights work well. And they will keep the plant happy through the winter when there’s little sun.

You can use them to supplement whatever light the comes int through the south facing window.

Temperature

The Mexican Fence Post Cactus thrives in hot and dry environments. This comes as no surprise as we’ve all seen the kind of climate conditions deserts have on TV and in the movies.

This is its native habitat.

As such, it likes this kind of weather to grow optimally.

This is why its ideal temperature range is between 70 and 85 degrees Fahrenheit. Of course, it can be left in higher temperatures as well with no problems.

But the opposite is not true.

To keep it healthy and growing well, try to avoid temperatures below 50 degrees Fahrenheit.

While it will survive here, it still start struggling. And you won’t see it do particularly well in these conditions.

That said, it is worth noting that it can tolerate as low ow 25 degrees Fahrenheit if push comes to shove. This is as far as its hardiness goes though.

Avoid leaving it in the cold of winter where there’s frost and freezing temperatures. It will eventually die there.

Instead, bring it indoors once the weather starts getting colder.

Note that while this sounds logical, it is not always possible in real life. That’s because the Mexican Fence Post Cactus can grow up to 20 feet.

As such, there will come a point where you just won’t be able to get it inside. Nor is there a pot to hold that kind of size.

Therefore, it will need to go into the ground.

Once it gets that big, it is best to gift the plant to a friend who has an outdoor garden that with the right climate conditions.

Humidity

The other striking difference between the Mexican Fence Post Cactus and your tropical indoor plants is humidity.

While many tropical plants love high humidity because they come from the rainforest, that excess humidity is not something the Mexican Fence Post Cactus enjoys.

Instead, it prefers a more moderate to slightly high humidity. Its ideal humidity is 40% to 60%.

Try to avoid going over 60% since this can cause problems.

It can lead to stem rot, pests and diseases like mold, fungi and bacteria.

On the other hand, it also struggles with humidity below 40%. And if this happens, you’ll need to help it out a bit.

Misting is usually the simplest way to increase humidity around the plant.

But be careful with misting too much or misting too often. This can lead to fungal or bacterial infections.

How Often to Water Mexican Fence Post Cactus

The Mexican Fence Post Cactus is the perfect plant to leave the house and go on vacation. It won’t need watering before. Nor will it need any help from neighbors to water it.

In fact, by the time you get back, it may still not need watering.

That’s the kind of conditions it likes.

In the desert, which is its native habitat, it can go for months without water if the need arises.

Indoors, you can water it occasionally. Once every 2-4 weeks will work during the summers. This is when the weather gets hot, and things can dry up.

On the other hand, during winter, only water once every 4-6 weeks.

Make sure to only water when the soil has already completely dried. Never before that.

Watering it too often is the biggest problem home growers have with cacti. That’s because they don’t like damp, moist or wet soils.

If you leave them there, they’ll eventually develop root rot.

As such, always stay on the very dry side when it comes to water.

Another thing to watch out for is to never water at late in the day or at night. The temperature gets cooler then and there isn’t much light to let the soil dry.

This leaves the cactus in a damp environment overnight.

Outdoors, it thrives in areas with minimal rainfall. Unlike most houseplants that enjoy about an inch of rainfall weekly, that amount of is too much for the Mexican Fence Post Cactus.

Therefore, you’ll want to keep it away from getting wet if you live somewhere with regular rain. You can keep it under a cover or something to keep it from getting wet as much.

Mexican Fence Post Cactus Potting Soil

The Mexican Fence Post Cactus needs very well-draining soil. This is a step further down from the regular well-draining soil most houseplants including Aroids like to have.

As such, it has even better drainage.

You don’t want to use this kind of soil on your other houseplants, at least not without amendments to retain some extra moisture, since it will dry out their roots.

But this is perfect for the Mexican Fence Post Cactus.

Using very well-draining soil helps keep the plant’s roots dry so they don’t end up rotting.

The good news is that it is very easy to get the right soil for the Mexican Fence Post Cactus. All you need to do is go to your local nursery and ask for cactus mix.

Never use regular potting soil for this cactus as it will hold doo much moisture. Additionally, the Mexican Fence Post Cactus needs very loose and very well-aerated soil.

If you want, you can make your own cactus mix at home as well.

Here’s a simple combination you can use:

3 parts potting soil
3 parts coarse sand (you can use gravel instead)
2 parts perlite (or you can substitute with pumice)

Of course, one critical thing you should never miss with this the Fence Post Cactus is the pot has to have drainage holes at the bottom to let the excess liquid get out.

Fertilizer

The Mexican Fence Post Cactus does not need fertilizer.

Simply put, the plant will be okay and grow well even if you don’t feed it. This is another reason why cacti are popular houseplants.

They are very low maintenance.

That said, you can feed the plant during spring and summer but only on occasion. Don’t fertilize it like you would your other houseplants which go on a regular basis during the warmer months.

Just once in a while does help.

Never overdo it either.

You can use a cactus fertilizer. These are readily available in nurseries and garden centers.

Never feed the plant during fall or winter.

Pruning

The Mexican Fence Post Cactus can grow to 20 feet tall outdoors in its native habitat.

Of course, it likely won’t be able to get that big even in your garden unless you have the perfect conditions matching it the Mexican desert.

If you leave it in a pot, it will reach a smaller size then in the outdoors as well.

That said, it may eventually grow your home indoors or apartment if you don’t have a large enough garden to transplant it to.

But in the meantime, you can keep it in a pot.

Given the right conditions, the Mexican Fence Post Cactus is fast growing. In its native habitat, it grow up to 3 feet in one growing season.

Of course, you’re never going to see that kind of growth spurt at home in a pot. So, don’t worry about coming home one day and having a mid-sized cactus in the living room all of a sudeen.

As far as pruning goes, there’s no need to prune the plant.

Again, this is just another reason why cacti are low maintenance.

How to Propagate Mexican Fence Post Cactus

Mexican Fence Post Cactus propagation is often done via cuttings. This is actually a good way to reduce the size of your cactus when it gets too big.

The best time to propagate the plant is during spring.

Here’s how to propagate the Mexican Fence Post Cactus.

You don’t have to unpot the plant. Just keep it in its place.
Then deicide where you want to cut the Mexican Fence Post Cactus. You can cut it in half or take just a smaller part. Some growers will cut near to the base then split up the upper part it multiple cuttings. It is up to you.
Don’t worry about the mother plant since it will grow in time.
Take a sterile knife and cut the cactus at your desired points.
With the main cutting you can cut that into multiple cuttings as well if you want to grow more than one new plant.
Finally, plant each of the cuttings in very well-draining soil. You can plant the top standing up in soil. similarly, you can plant the others horizontally on the soil. These will grow in an L-shape going up in time.
Don’t water the new plants for at least a month.

How to Repot or Transplant Mexican Fence Post Cactus

The Mexican Fence Post Cactus will get big. And depending on how many cacti you have in the pot, you may run out of space sooner or later.

Note that while some people only grow one Mexican Fence Post Cactus in a pot, it can look sad and lonely there.

So, in many cases you’ll see multiple cacti in one pot giving you columns of Mexican Fence Post Cactus.

Of course, this also means larger pots. But they do look more beautiful together.

Repotting is usually needed every 1 to 2 years. But again, its growth will significantly vary on its living environment and care.

So, move the cactus to a bigger pot when it outgrows its container.

When repotting, use good sized gloves so the prickly spikes don’t get to your fingers.

Carefully take the plant out of the pot. It will have a deep pot if the plant is a few feet tall. This can make it hard to remove the soil without damaging or tearing plenty of roots.

So, just water the root ball with a hose to loose the soil so you can split them all up.

Then fill a new put with very well-draining soil up to near halfway. Then plant each of the Mexican Fence Post Cactus in.

Finally, pat down the soil but don’t tamp it too much. The plant hates compacted soil.

Instead, it wants somewhat loose soil that allows for lots of airflow to the roots.

Is It Toxic/Poisonous to Humans, Cats & Dogs

Keep the plant away from young children, cats and dogs. While it is not toxic, its external surface has lots of small spikes that are dangerous for children and pets to play around.

Mexican Fence Post Cactus Problems & Troubleshooting

Pests

Scale and mealybugs like to attack the Mexican Fence Post Cactus. As such, regular pest inspection is necessary.

With scale, you need to look closely. Often, they will stay at the base of the plant.

This can keep them hidden due to the soil or if you don’t look all the way down. And because they look like brown specs on the surface, if you don’t observe closely, you’ll think it’s just dirt, dry soil or sand sticking to the cacti.

These will spread upwards over time if you don’t spot them and get rid of them.

And they will cause growth issues as well as other problems.

So, if you can’t figure out what’s happening, check for pests.

Diseases

Root rot is something you want to always watch out for.

It is very easy to overwater the Mexican Fence Post Cactus because of its very low water requirements.

Never treat it like a regular houseplant when it comes to water. Or else, you’ll end up giving it too much moisture which leads to problems.

Always stay on the dry side with this plant.

Mexican Fence Post Cactus Care – Growing Pachycereus Marginatus