Mexican fence post cactus of the Cactaceae family is a desert succulent that grows up to be as tall as a single-story building. Not only can you keep it indoors initially, but they are sure to make people turn their heads while standing outdoors in your garden.
As a desert plant, this Lophocereus genus plant has certain nitpicks that you need to be aware of before growing it. Our experts have strived to bring you this ultimate guide for growing this unique cactus.
JUMP TO TOPIC
- What Is Mexican Fence Post Cactus?
- Mexican Fence Post Cactus Care
- Water Requirements
- Light Requirements
- Soil Requirements
- Temperature Requirements
- Humidity Requirements
- Fertilizing Requirements
What Is Mexican Fence Post Cactus?
The Mexican fence post cactus is a plant that can achieve preposterous heights of about 20 feet. It grows in the form of tall columns with green-gray ribs and white spikes. Its scientific name is Pachycereus marginatus, and it also goes by the Latin name Lophocereus marginatus.
Mexican Fence Post Cactus Care
This plant becomes up to 20 feet tall when grown under the best possible conditions. Its horizontal spread alone is about 6 feet in total. No wonder it is considered among the giants of the cactus world.
The growth rate of this cactus is also pretty amazing. It grows rapidly during spring and summer at an average of 3 feet per season, then it undergoes a time of dormancy from fall until the next spring.
The fence post cactus likes to grow under the brightest direct light that you can give it. Water it only sparingly when the soil gets all dry. Keep humidity a bit lower and temperatures up to 60 to 80 degrees Fahrenheit. Make sure your soil is rich in sand and drains water as soon as possible.
Your Mexican fencepost cactus doesn’t need to be watered that much. Like all cacti, it tolerates drought much better than overwatering. You only need to water it once every second or third week in the summer and only once every four weeks during winter.
How To Water This Plant
You should water this plant by first checking the soil out. It needs to be dry to the bone. A moisture meter will tell you when it is so. You can use a stick instead to check the dryness by putting it in the soil and seeing whether it comes out with dry or moist soil.
The water needs to be poured only in a moderate amount and very slowly. After some time passes and the water drains out of the soil, remove the water collecting saucer from under the pot. If the pot stays in contact with water for long, this will lead to overwatering and rot.
What Type of Water To Use
The water type your plant needs should be clean and free of salts and minerals. You can use water that is filtered out of reverse osmosis. Distilled water is a suitable choice too but can be a bit expensive to buy regularly.
If the cactus is grown outdoors, occasional rainwater would be enough. When watering, take care that the temperature of the water is lukewarm. This plant would accept neither hot nor cold water.
This plant needs full sunlight for a minimum of six hours each day. There is no such thing as too much sun for this desert plant — the more, the merrier. It would help if you were more concerned about underlighting this plant.
Proceed below to find some useful information regarding the perfect light for this plant.
Growing It Outdoors
Outdoors is the perfect spot for growing this cactus. It stays happy just standing outside on your lawn and taking in as much sun as possible. It grows best when it receives about eight to ten hours of light a day.
Don’t place this plant where it is shaded by something like larger trees or a northern-facing wall. It will not take kindly if it does not receive the maximum amount of light for at least six hours each day.
Growing It Indoors
If you want to grow this plant inside the house, choose a room with a large window facing the south. This is because this is the only window that receives light adequate for this cactus.
The light from the rest of the windows is just too mild for this one. Secondly, place the plant as near the window as possible, preferably on the window sill, and do not cover the window with shade during the morning hours.
Growing It Under Artificial Light
Sometimes, sunlight from the windows will not be enough to grow your large cactus indoors. This calls for substitution with artificial grow lights. They emit light of specific wavelengths that help your plant grow.
These lights come in two main forms: fluorescent and LED lights. LED lights are more in vogue because they are more reasonable and energy-efficient. You can place them right above your plant at 20 inches.
If artificial lights are placed on one side of the plant, you must keep rotating it daily so that all sides get equal light. You still need to place the plant near a window even with artificial lights.
Like its native desert soil, this cactus, when grown at home, should also have a soil that is porous, nutritious, and rapidly draining. The pH of this soil needs to be between 6.1 to 7.8. The overall texture of the soil should be sandy. Another reason for choosing sandy soil is that this plant’s short roots don’t like being cramped and compacted.
Plant markets have a variety of cacti and succulent mixes available that you can use. Ordinary potting mixes are not healthy for Mexican cactus. Usually, cacti mixes contain clay, sand, and silt in the ratio of 20:40:40.
However, making your potting mix for your special cactus friend is even better. You can learn how to make this below.
Making Your Soil Mix
The easiest method is to add peat and perlite in an equal ratio. For nutrition, add mulch or organic compost. You can add coco coir or charcoal in a small quantity as well.
There is another method to make your soil in which you take one part cactus mix then add one part perlite or pumice and half part sand to it. Lastly, place some organic compost in the soil as a nutritional additive.
This plant wants a hot temperature to grow to its best potential, around 70 to 80 degrees Fahrenheit each day. Keep in mind that this is a desert plant and will not tolerate low temperatures for long. It might survive at temperatures as low as 50 degrees Fahrenheit for some time, but not for long.
The real problem occurs when it is exposed to temperatures as low as 25 degrees Fahrenheit. The plant’s cells will start dying, making it impossible to save it.
Here are some of our favorite tips regarding providing the right temperature range for your plant.
- An Indoor plant should be kept far away from cold air sources such as vents and air conditioners. Ideally, keep them in a room that stays mostly warm throughout the day.
- It is also best to move this cactus indoors when a temperature drop occurs.
- If it is impossible to move inside the house, then cover the plant to protect it from cold. You can use a burlap sack or a frost blanket for this.
- Even though it can tolerate high temperatures, we still don’t recommend placing it directly near a radiator or a heater.
Post cactus grow best when humidity around them is within 40 to 60 percent. Fortunately, this is exactly the range of humidity that you will find in most homes. Still, it is prudent to have a hygrometer at home to monitor your air’s moisture closely.
If humidity is more than 55 percent, your cactus is at an increased risk of being overwatered. It is also more susceptible to attacks by pathogens like fungi and bacteria. You will have to use a dehumidifier to reduce humidity to 40 percent.
It will be rare to see humidity falling below 40 percent unless you live in an extremely dry area. If so, then misting the cactus once a week should be enough. You can take a dry towel and use it to wipe the plant alternatively.
Technically, this plant will continue growing despite not being fertilized. However, fertilizer twice or thrice during each growing season cannot harm. It is best to use organic fertilizer, which is the safest for your cactus roots.
If you must use a synthetic one, use a balanced fertilizer with an NPK ratio of 5:5:5. Even then, it is best to just preemptively dilute the fertilizer using salt-free water.
Here are some of our top fertilizing tips:
- Never fertilize dry roots.
- Always water the plant copiously before fertilizing.
- Stop all kinds of fertilizer use during nongrowing periods in the fall and frost.
Pruning is generally unnecessary for this plant unless you want to grow it into a specific shape. If some part has been unaffected by disease, it might need to be pruned off as well. Always use clean and sharp tools for pruning your plants.
You can transplant this cactus by taking it out of its current pot and transferring it to a larger or better pot. Mostly, you will need to transplant this cactus when repotting. A diseased plant needs to be transplanted into a new pot as part of its treatment.
Transplanting or repotting this cactus should only be done after two to three years when the plant outgrows its old pot. Roots begin to creep out of the drainage holes or the rims of the old pot.
We have divided transplanting cacti into three main steps given below.
Select the Right Pot
The first step is to pick the perfect pot for your Mexican fence post cactus. We suggest you always go for a clay or terracotta pot. Ceramics and plastics should only be your second best option. Whatever you do, do not plant this cactus in a glass or metal pot.
The size of the pot should be about 5 inches for this plant. Experts suggest maintaining a distance of at least 14 inches from the stem to the pot’s rim. A pot that is too large will lead to water accumulation, so choose wisely.
Select the Right Time
Timing is the key here. Spring or early summer is the best time to transplant a plant for repotting. This is when this desert’s succulent is at its rapid growth.
If you transplant late during the year, your plant will take longer to recover from transplant shock. Of course, a diseased or disturbing plant can be transplanted anytime to save it from dying.
Follow the Guide Below
Here are some of our top tips to help you make a successful transplant.
- Water the pot a bit extensively one day before transplanting. This will strengthen the roots and loosen the soil up a bit.
- Take a rake to remove 25 percent of the soil from the top carefully.
- At this point, your plant will come out of the pot pretty easily.
- Take a larger pot in case of repotting and a similar one and fill it halfway with the right potting mixture.
- Place the roots of your cactus in the pot and fill the rest of it up with soil.
- Take great care of your plant initially so that it survives well.
If you have this tall cactus at home, you should propagate new plants yearly. Spring or early summer is the ideal time of the year to carry out this endeavor.
Gather all the right information regarding propagation from the sections coming up ahead.
– Propagating Through Cacti Offsets
Offsets are tiny bite-sized plants growing at the base of an adult plant’s stem. They can be removed from their parent plant and used for propagation.
Carry on reading as we take you through a detailed step-by-step offset propagation guide.
- Identify one or two offsets at the base of the stem that you want to use for propagation.
- Wear rubber gloves to protect your hands from the thorns on your fence post cactus.
- Take clean gardening scissors out of the shed and snip off the chosen offsets. Cut right where they emerge from the stem.
- The next step is to store them for a few days in a dark and dry place until the cut end heals.
- After the cut has healed, which you can check by callus formation, apply rooting hormone on the cut end.
- Take a new pot and spread a layer of gravel at its bottom. Then fill it to the top with your preferred soil, making a hole in the center. Into this hole will go your offset along with slight watering.
- Keep immediately under the direct sun but hold off on watering for one to two weeks at least.
- The cuttings will take roots in two to six weeks, and you can resume a typical cactus watering regime.
– Propagating Through Seeds
Propagating a plant through seeds is harder than propagating via offsets. This is because seeds are hard to collect from flowers by yourself. Store-bought seeds might be low quality or old and not even germinate.
If you buy Mexican fence posts’ good quality seeds, follow the steps below to grow Mexican cactus.
- Take a transparent plastic jar that has a lid over it. Make holes in the lid and the bottom of the jar.
- Fill the jar with a sandy mix made of either cactus or succulent mix.
- Sprinkle some water over your soil such that it dampens slightly.
- Now insert seeds one by one into the soil, measuring a distance of one inch between them.
- Put the lid over the jar on your brightest window sill. Every week, take the lid off to allow some air exchange in the soil. If the soil is excessively dry, sprinkle more water to add moisture.
- The primary requirements for the seeds to grow are high temperatures and proper humidity levels. Propagating seeds in a lidded jar is a good idea.
- Your seeds will germinate in about four to six weeks, but take note that you can only transfer the new plantlets in their pots after eight to ten weeks.
Pests and fungal infections are the two most common problems you might face with this plant. Here are both of them discussed in detail.
It is not rare for household plants to get infested by pests occasionally. Most of these pests suck on the sap flowing through the plant, weakening it over time. The plant’s growth slows down over time, and yellow spots will start to appear everywhere.
Aphids, mealybugs, and spider mites are the most common pests attacking your cactus. Aphids are tiny insects that are white to green in color. They are easy to spot and cause yellow discoloration in the plant.
Mealybugs are white bugs resembling cotton balls that can be seen roaming about the grey-green cactus. It, too, produces yellow spots on the leaves. In severe cases, leaves might start dying. You might also see some white spots on your cactus.
Red spider mites are amber-colored insects that remain mostly stationary on your plants. It feeds vigorously on the plant, leading to stunted growth in the long run.
How To Get Rid of Pests
You will be happy to know that successful and effective pest control is quite easy to perform at home. Here are the key steps you need to take in this regard.
- First, try to remove as many of these pests as possible. You can use a scraping knife, tweezers, or a brush to remove them.
- Take a watering hose and wash your plant with insecticidal soap. Many pests will also be washed off by this method.
- To get rid of the eggs, dip a brush in neem oil or isopropyl alcohol and apply it to the plant. Neem oil is a much better and more organic substitute for alcohol.
- It would be best if you also started a weekly insecticidal spray regimen to keep these pesky pests off your plant.
– Root Rot
Root rot is a fungal disease caused by a variety of fungi. These fungi attack your plant when the soil is allowed to remain wet for a long time. This can be due to either overwatering the soil by not allowing it to dry fully. It can also be due to an incorrectly-sized pot so large that water evaporates after a very long time.
Sometimes the drainage of the pot is so poor that water keeps on accumulating. Humidity levels above 60 percent is also a cause for rot among cacti.
Signs and Symptoms of Root Rot
The appearance of yellow, brown, or black rot spots is a tell-tale sign of fungal root rot. Try sniffing your plant, and it will smell rotten and bad. The usually stiff and upright leaves will start to weigh down and droop.
The Best Way To Treat Root Rot
Before treating root rot, you must remember that saving your plant will not always be possible.
- First, depot the diseased plant from its old soil and lay it on a piece of paper.
- The roots will appear all black and mushy. Keep changing the newspaper every few hours until the roots dry out thoroughly. This might take up to three to four days in total.
- You need to cut off the most rotten parts of the roots and the stem and leaves. Spray the whole plant daily with a strong antifungal spray, the best one being the liquid silver one.
- After three to five days, transplant the whole cactus into a new pot. Keep up the antifungal regimen and refrain from watering for a couple of weeks at least.