Much Ado about the Acanthocereus Tetragonus ‘Fairy Castle Cactus’ 101

Acanthocereus tetragonus—once known instead as Cereus tetragonus but commonly known to laymen as the Fairy Castle Cactus—is a tall cactus of the columnar variety that’s native to the Lower Rio Grande Valley of the State of Texas as well as Southern Florida.

It can also be found in Northern South America, the Caribbean, Central America, and Mexico as well as the U.S. A healthy cactus is capable of growing hundreds of green branches.

Quick facts about Fairy Castle Cactus 

The Fairy Castle Cactus or Fairy Castle is a cactus that can be grown indoors as long as you have enough lighting fixtures inside or have bay windows to let the sunlight in.

With that said, it grows best outdoors with partial shade and partial sunshine rather than full sunshine or full shade. The miniature plant can get as tall as 6 feet or 1.8 meters. It’s not cold hardy and can only take Zone 10a temperatures.

Planting

#1. When to plant?

You should plant the Fairy Castle Cactus during the spring and fall. It actively grows during those seasons. It survives summer well enough since it’s a cactus.

However, it’s usually devastated by winter, especially in areas where the weather can reach temperatures way below 30° F or -1.1° C (which is around its minimum temperature limits).

#2. Where to plant?

Plant it indoors if your area in the world receives frosty or icy winters, since those are death knells to this particular type of plant. Additionally, if you do decide to plant it outdoors, do so where it can get a daily dose of 6 hours of full sunlight or partial sunlight and partial shade. Keep it away from air conditioning or vents.

#3. How to plant?

Plant its seeds or stem cuttings indoors in a pot because it grows well indoors, making it the perfect plant for beginners to handle. Just avoid over-watering it but don’t forget to water it once that soil is completely dry. Just sow the seeds and put a light layer of sand on top. As for stem cuttings, just place the stem onto the soil without breaking the stem.

Care

#1. Soil

A bag of pre-mixed cactus soil (part loam and part sand) or gritty compost that can drain itself excellently is good enough to allow the Fairy Castle to thrive without worrying about over-watering or root rot. Efficient water drainage and letting the soil breathe and dry out is key.

#2. Light & Temperature

Its sunlight requirements range from partial to full sunlight. It’s quite hardy against hot climates with loads of sun. The temperature range that the Fairy Castle can survive in is for the USDA hardiness zones of 10a to 11b. In other words, it can take temperatures ranging from 25° F to 50° F or from −3.9° C to 10° C.

#3. How To Water For Fairy Castle Cactus & Humidity

Water this cactus like a typical succulent. Water it without flooding on gritty, free-draining compost or pre-mixed cactus soil.

It’s easiest to take care of the cactus during frost-free winter because you cut down the amount of water needed in this season in half. It doesn’t require high humidity a la tropical weather either.

#4. Fertilizer

It grows during spring so the best time to fertilize it is during this season. Specifically look for a cactus fertilizer in order to get the best results. Feed the cactus in a monthly fashion. Alternatively, you can irrigate it with a diluted liquid fertilizer mix that’s about half-strength. Stop feeding it fertilizer during the winter season.

#5. Propagation

The cactus is propagated by seeds from its flowers or by cutting its stems and letting those grow into a new plant. It’s quite the sun-hardy plant that can grow hundreds of green branches like towers or turrets reaching up to 6 feet or 1.8 meters tall with the right non-frosty conditions.

#6. Pruning

Pruning won’t help because it’s unnecessary. However, once it develops rot, pruning can save your plant’s life. Use a sharp knife or clippers and cut at a 45° angle to make sure your cut is clean and the resulting stub can still heal.

Problems

#1. Growing Problems & Diseases

Like other succulents, when you over-water the Fairy Castle, it tends to develop root, stem, and leaf rot. It was designed to grow in the desert with little water. When you give it an over-abundance of water, it’s bad for it. Water it properly to prevent root rot and cut away the parts of it that are rotting.

#2. Pests

Brown spots could appear all over your Fairy Castle if it’s being eaten by scale or mealybugs. It could also be a fungal infection that’s slowly killing it on top of root rot that happens when you over-water it. Use neem oil and practice proper succulent watering habits to prevent these pests from attacking your plant.

FAQs

#1. Why is Fairy Castle Cactus named as such?

The Fairy Castle Cactus gets its name from its columnar branches that clump together upwards vertically, like turrets of a miniature medieval castle or a castle fit for a tiny fairy king. Each stem has five sides with short spines or thorns growing along its ribs.

#2. When does the Fairy Castle Cactus bloom or get flowers

It takes about a decade for a Fairy Castle Cactus to produce flowers that are typically yellow or white in color. Therefore, it rarely blooms. When you buy this cactus and it has flowers it’s usually the hot-glued variety using fake yellow or pink flowers to make it more decorative.

#3. Why is my Fairy Castle all twisty?

Like with oregano, your Fairy Castle Cactus tends to grow and follow the sunlight. If part of it is hidden in the shade and another part of it is in full sunlight, it might twist its body towards the part with light in order to get maximum rays. To prevent this twisted appearance, prune and/or place your plant in direct or partial sun contact.

#4. Is the Fairy Castle Cactus toxic to humans and animals?

No, it’s not. It’s generally nontoxic to both humans and other animals. It’s unlike other succulents that have enough toxicity to make them dangerous to your pets when eaten. Then again, since it’s a cactus, eating it spines and all is a bad idea. Regardless, you shouldn’t eat it or consume its juices.

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