Mexican Fence Post Cactus Care Guide — Our Top Tips!

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I am hooked on Cacti at the moment! Strolling around an outdoor market recently, I came across the stunning Mexican Fence Post Cactus.

They had a small baby plant in a pot that I just had to buy for my indoor collection.

This plant can grow to heights of 20 feet (6m)! So, after a year or two, when it reaches about 1 or 2 feet (30cm to 60cm), I will probably have to give it to a friend to plant into a garden.

In the meantime, I will see how it does as a taller backdrop to my smaller cacti. 

The Latin name is Lophocereus marginatus. It is also known as Pachycereus marginatus.

More common names are Organ Pipe and  Organ Cactus. The Fence Post reference comes from the fact that they make great outdoor hedges or barriers. 

This plant has a lovely dark green-gray columnar body with well-defined ribs and white spines along the edges. They offer bell-shaped pink-red flowers that bloom in Spring.

The plant is native to Mexico and the southern USA, where it grows in dry, hot desert regions. 

Let us take a closer look at how to care for your Mexican Fence Post Cactus. 

Mexican Fence Post Cactus Care

Plant the Mexican Fence Post Cactus in loose, well-draining soil and allow it to dry out between waterings. It needs at least 6 hours of full sunlight daily. Fertilize sparingly with an organic cactus mix during spring and summer. Thrives best in temperatures between 70°F and 80°F (21°C to 27°C). 

Soil

The Mexican Fence Post Cactus grows naturally in the desert, where it is very hot and very dry. It wants very well-draining soil that dries out completely in between waterings. 

I use a cactus mix that I purchase from my local nursery. A cactus mix offers a combination of clay, sand, and silt in a ratio of 20%, 40%, and 40%. You do not want to use a regular potting mix for this plant. It requires a very loose, very well-aerated soil type. 

I also make my own cactus mix. This is made up of a 50% to 50% combination of peat and perlite. To increase drainage, I add in coco husks.

For added nutrients, I throw in mulch and organic manure. The Mexican Fence Post Cactus is very hardy and will not stress if there is minimal fertilizer in the soil. 

Mexican Fence Post Cactus soil tip: Another good soil mix for your Mexican Post Cactus is 50% coarse sand and 50% leaf mulch. 

Light

The Mexican Fence Post Cactus loves the sun. It is more than happy to stand in full sunlight all day long. Place yours in a spot that gets at least 6 hours or more of direct sunlight. A south-facing window sill is ideal. 

If you are planting it outdoors, ensure that there are no large trees or structures nearby that will cause the shade to fall onto the plant as the sun moves. 

You will not need to worry about too much sun for this plant. So there is no need for sunscreens or filters. 

If your home is dark in winter, why not consider using a grow light? Grow lights can be Fluorescent or LED lights. LEDs are becoming more popular because they use up less electricity and are eco-friendly. 

Mexican Fence Post Cactus light tip: Some grow lights come in the form of attractive lamps that can be clipped onto a shelf edge. Remember to rotate your plant every few days so that it is not only exposed to light from one side. 

Watering

As we all know, water is not commonly found in deserts and the Mexican Fence Post Cactus can survive for months without water if necessary.

That being said, you can water your indoor plant in the summer months. Give it a watering once every 2 to 4 weeks. Allow the soil to dry out completely in between waterings. 

Reduce watering to once a month or even less in winter. 

Don’t water your plant at night. Temperatures are cooler at night and water in the soil will become even colder. 

Don’t overwater your Lophocereus marginatus. Your plant will not be happy and may even die, especially if the roots start to rot in damp soil.

Ensure that your plant container has adequate drainage holes at the base and they are not blocked by sand. It is vital that water flows out of the container and does not accumulate at the base. 

For outdoor Mexican Fence Post Cactus plants, normal to minimal rainfall should be fine. This plant won’t do well in a tropical-type rainfall climate. If you get a lot of rain, consider growing it in a pot on an enclosed patio if you have the space. 

Mexican Fence Post Cactus water care tip: If you are off on a vacation and need to leave your plant for a few weeks, don’t stress. It can survive without water for longer than that. 

Temperature

Think hot and think dry. The Mexican Fence Post Cactus wants heat whenever possible. It thrives best in temperatures between 70°F to 80°F (21°C to 27°C), or even higher. 

It won’t do well in temperatures that constantly fall below 50°F (10°C). 

It is hardy down to cooler temperatures of 25°F (-3°C) for very short periods of time. Do not let your Mexican Fence Post Cactus stand in the frost, it can get damaged and may even die. 

Mexican Fence Post Cactus temperature care tip: If the weather turns cold and your plant is outdoors, consider protecting the tips of the plant by covering them with Styrofoam cups.

Humidity

The  Mexican Fence Post Cactus enjoys a dry and hot climate. Humidity must never be too high, this is not a tropical rainforest plant.

An average home will have humidity levels of around 40% to 60%. This will be ideal for your cactus. Anything over 60% will be too damp and may even become a health hazard for people in the home. High humidity tends to breed mold and bacteria. 

If you have a very humid, hot home and are using an air conditioner to reduce temperatures, ensure that your plant is not standing in an icy draught. 

Mexican Fence Post humidity care tip: If the humidity is very low, at under 40%, consider giving your plant an occasional light spray mist. 

Fertilizer 

For those people who prefer not to fuss too much with their plants, you will be happy to know that the Lophocereus marginatus will survive with no regular feeding routine.

It does, however, benefit from an occasional feed in the spring and summer months. Do not fertilize your plant in winter, it can damage the plant. 

When buying a ready-made fertilizer, I always look for a natural organic mix. I stay away from chemical mixes whenever I can. 

The best cactus fertilizers are made up of a combination of potassium, nitrogen, and phosphorus. Look for a special Cactus Fertilizer at your local nursery or farmer’s market. Home-made fertilizer is also great to use. If you have a garden, why not consider setting up a small compost-making kit and make good use of fallen leaves, grass cuttings, and dead flowers?

Care tip for feeding Mexican Fence Post Cactus: Fertilize sparingly only during the growing season. 

Propagation

The Mexican Fence Post Cactus can be propagated from cuttings. This may sound daunting to a first-timer, but it is really easy to do.

Propagating is a fun and rewarding hobby. You can offer your new plants as gifts to family and friends, or expand your existing display without spending any money. 

Further on, I give a step-by-step guide on how to propagate your Mexican Fence Post Cactus.

Growth

In natural desert regions, the Mexican Fence Post Cactus is an imposing plant that can grow to heights of up to 20 feet (6m) or even more. It produces clusters of tall, columnar trunks that resemble a pipe organ. 

In a pot, your plant can grow to a height of up to 2 feet (60cm). It has a sturdy body with a main stem that can become as wide as 4 inches (10cm).

The shape is well-defined with 5 to 7 deep-green ribs. Along the edges of each rib are white spikes set in woolly areolas forming a very attractive display. These spikes are prickly – so be cautious when handling the plant. 

In Spring, a mature Lophocereus marginatus will produce lovely tubular-shaped, pinkish-red flowers. The flowers grow out from the edges of the ribs almost horizontally. After blooming, you will notice that the cactus develops spiny, yellowish-red fruit with black seeds. 

If grown outdoors, the Mexican Fence Post Cactus makes a fabulous fence to line a wall or provide a barrier to cover an unsightly view of neighboring properties! Because it grows so tall with thick stems, it will create a fabulous dense wall that can become almost impenetrable.

Indoors it is great to add a tall backdrop to a cactus display. It also looks great on a patio corner that would otherwise be dull and boring. 

Potting

The Mexican Fence Post Cactus looks awesome in any decorative container. It has a very distinct thick, columnar shape, so choose a pot that enhances the shape and is not too large or wide. 

Place a layer of loose granite chips or small pebbles at the base of the pot, this will help with drainage and can prevent the drainage holes from getting blocked up by the finer sand. Half fill the pot with your cactus mix and water well. 

Place the plant into the center of the pot – don’t forget to wear your protective gloves, the spikes can prick you. Using a scoop, fill in the pot with cactus mix around the plant. Do not press the soil down tightly, it should remain loose to allow for water drainage and air flow.

Repotting of your indoor plant may become necessary if the plant starts to outgrow its container. Plan to do this in spring after the winter hibernation season. If your plant starts to get very tall, why not consider a floor-standing pot? You can let it grow to a height of many feet to create a fabulous focal point in your living space. 

If you are planting outdoors, prepare a suitable size hole. Half fill with cactus mix and water it. Place the plant into the hole and cover with soil. Ensure that the spot you have chosen gets full sun. 

Mexican Fence Post Cactus potting care tip: Glazed pots tend to retain water for longer. That is because the sides are sealed and water cannot evaporate as fast as it does in an unglazed, porous pot. Rather choose a porous pot for your plant. 

Mexican Fence Post Cactus in-depth propagation guide

Propagate Mexican Fence Post Cactus from offsets

• A mature Mexican Fence Post Cactus will start to grow stems off the main stem 
• The stems can be removed and used to create new plants
• Plan to do this in early spring to late summer
• You do not have to remove the mother plant from its container
• Ensure that you have a pair of thick, protective gloves, as the spines can prick you 
• Using a sharp sterile knife cut off an entire stem where it attaches to the parent plant
• Do this as cleanly as possible to create a straight edge 
• Carefully place the cutting into a dry container
• Leave it in a warm spot 
• You will notice that after a few weeks a callus will form over the cut surface
• Check that the callus has healed and is dried out 
• A cactus with dried ends forms roots far more easily than one with wet ends
• Prepare your pot with a cactus mix
• Water lightly 
• Place your cutting into the soil and anchor if necessary to hold it upright
• Stand in a warm spot with lots of sunshine 
• Don’t water for at least 4 weeks, then water well and allow to dry out

Common problems with Mexican Fence Post Cactus

Pest Control

Checking your plant regularly for pests is a must. If caught early on, pests can be removed. The most common pests that attack the Mexican Fence Post Cactus are soft scales and mealy bugs. 

Soft scales are sap-sucking pests and are close relatives of Aphids. These undesirable creatures have scales that protect them from the environment. They latch onto the plant, feed, and lay eggs. If you are brave, you can pick them off with your fingers. You can also use tweezers. I prefer to use a spray of diluted rubbing alcohol. After spraying, I brush them off with a medium to hardpaint brush and then wash down the plant with water.

Stems turn yellow and mushy 

This is a sign of too much water or conditions that are too humid. Your Mexican Fence Post Cactus is a desert plant that requires a hot and dry environment. Try repotting and standing in a more suitable position with full sun. 

Tips to grow Mexican Fence Post Cactus problem-free

• Plant into a cactus soil mix
• Avoid over watering 
• Avoid very humid and damp conditions 
• Never allow the roots to stand in water
• Give your plant at least 6 hours of direct sun every day
• Protect from frost if you can 
• Fertilize sparingly only during spring and summer 
• Use natural insecticides to keep pests at bay 
• Choose a clay or terracotta pot that allows the water to evaporate through the sides

Read about Pachycereus marginatus care next.

Frequently asked questions about Mexican Fence Post Cactus

Can Mexican Fence Post Cactus grow indoors? 

Mexican Fence Post cacti grow indoors but are more commonly found outdoors. Remember that in its natural habitat, it can grow very tall – up to 20 feet (6m) or more. 

Is it easy to care for Mexican Fence Post Cactus?

The Mexican Fence Post Cactus is the perfect plant for beginners or people who don’t have too much time to fuss over their plants. Hot, dry conditions make it happy. You can even neglect it for weeks, and it will still be fine. 

Is Mexican Fence Post Cactus prickly? 

The spikes of the Mexican Fence Post Cactus are prickly and sharp. This is not the ideal indoor plant to keep if you have pets or children in the home. 

Conclusion

The Mexican Fence Post Cactus is a very attractive plant that makes a great indoor backdrop to smaller cacti plants. It can grow tall but is a slow grower.

The deep-green color and interesting symmetrical shape make it a conversation piece. When it blooms, it offers lovely reddish-pink flowers. 

I do love a plant that does not require too much fuss and care. My Mexican Fence Post Cactus grows happily in full sun and is not bothered if I forget to water it. 

My Mexican Fence Post Cactus stands next to an Acanthocereus tetragonus, better known as a Fairy Castle Cactus. This lovely plant offers branches that clump together in a whimsical shape, resembling the turrets of an enchanting fairy castle.