Fairy Castle Cactus, or Acanthocereus tetragonus, is a columnar cactus native to the southern United States, Mexico, Central America, northern South America, and the Caribbean. It gets its common name, Fairy Castle Cactus, due to its resemblance to the turrets of a medieval castle.
This cactus was formerly referred to as Cereus tetragonus. There is some disagreement among experts on how the Fairy Castle Cactus should be classified. Some scientists believe it should be classified as a cultivar of Cereus hildmannianus and refer to it as Cereus hildmannianus f. monstruosus.
A. tetragonus is a popular cactus among growers due to its easy care. It is an excellent cactus for beginner and expert gardeners alike. It’s commonly grown indoors as a houseplant, but it also does well when planted outdoors in the appropriate climates.
These captivating cacti are often seen local garden centers with brightly colored flowers hot-glued to their tops, but most growers choose to either remove these right away or allow them to fall off with time.
|Blooming:||Mid Summer to Spring|
|Light:||Full sun to partial shade|
|Water:||When the soil is completely dry|
|Propagation:||Cuttings and seeds|
Fairy Castle Cacti are slow-growing cacti, but they can reach up to six feet in height at maturity. Each stem has five sides and is lined with white, wooly spines along each ridge. The stems are vibrant green in color but will brown with time in a process called corking.
Over time, Fairy Castle Cacti produce branches, which has led to their turreted castle image.
As with most Cereus, the Fairy Castle Cactus is a night-blooming cactus. The flowers are large and either white or yellow in color. This cactus rarely blooms, and most individuals won’t bloom until they are at least ten years old.
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As previously mentioned, the Fairy Castle Cactus is a low-maintenance succulent that can be cared for by even the most inexperienced grower. With plenty of sun, the right soil, and proper watering techniques, this cactus will decorate your garden for years to come.
The Fairy Castle Cactus is like most cacti and does best with a lot of light. When grown outdoors, full sun is ideal. However, if you’ve brought home your cactus from the local nursery, it’s recommended to let it adapt to the full sun over a period of several weeks.
This slow transition to increased light is meant to prevent sunburn. Although Fairy Castle Cacti love sunlight, if they haven’t been exposed to full sun, they can become sunburned if they are thrust into too much light too quickly.
Since sunburn damage is irreversible, it’s best to avoid the risk by increasing sunlight slowly every couple of days until you reach a full day’s worth of sunlight.
When grown indoors, these cacti will grow best with as much light as possible. South-facing windows are perfect for the Fairy Castle Cactus to thrive.
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If your indoor space doesn’t provide your Fairy Castle Cactus with enough light, you should consider investing in a full spectrum grow light. They are relatively inexpensive and will allow your cactus to flourish no matter where it's located indoors.
Symptoms of inadequate light can include a fading in color or yellowing of the stems or branches. The cacti may also become etiolated or stretched out. The top growth will appear thinner than growth that occurred in periods of adequate light.
Most gardeners recommend allowing the soil to dry out between watering to prevent your Acantocereus tetragonus from being overwatered. Overwatering is the most common reason for dead cacti.
Standing water or prolonged periods of wet soil should be avoided at all costs. Too much moisture for too long will cause root rot, which is often fatal as the signs are not obvious until it’s too late.
The most common symptom of an overwatered cactus is actually a bit confusing for many gardeners. Overwatered cacti may first exhibit a plump appearance and significant new growth. Since they typically live in arid environments, they make use of the extra moisture as quickly as they can.
However, that lovely new growth comes at a price. Below the soil, your overwatered Fairy Castle Cactus’s roots are beginning to rot. As the rot moves up the stem, you’ll begin to see mushy branches and blackened stems.
By the time you see symptoms of rot above ground, it’s likely too late to save your cactus. To prevent overwatering, it’s crucial to check the soil before you water. If it’s moist, let it be.
It’s also important to realize that if your Fairy Castle Cactus is grown outdoors, there may be seasons where you need to water it more frequently. During the heat of the summer, for example, water evaporates quickly and you’ll need to give your cactus water more often than usual.
During winter, your Fairy Castle Cactus will grow very little. Combined with cooler temperatures, you will probably need to significantly cut back water until growth resumes in the spring.
Fairy Castle Cacti are not frost tolerant plants. When grown indoors, they can be sensitive to cold drafts and must be kept in areas where the temperature remains fairly consistent.
If planted outdoors, Fairy Castle Cacti need to be protected from freezing temperatures. If the weather dips down close to 30 degrees Fahrenheit, you need to bring your cactus indoors or cover it to protect it from freezing.
As with most cacti, heat is not a problem for the Fairy Castle Cactus. It can handle summers in Arizona without a problem, as long as you make sure it’s getting enough water.
The Fairy Castle Cactus shares the same soil needs as other species of cacti. Drainage is crucial to its survival, so it needs soil with large percentages of coarse sand, perlite, pumice, gravel, or bark. Water retaining materials like clay and peat moss should be avoided.
Commercial soil mixtures designed for use with cacti and succulents are great, but you can also make your own soil if you’d prefer.
If planted outdoors in the ground, drainage and soil quality should still be considered. Growing these cacti in raised beds or berms can help encourage drainage.
If planted in containers, you need to make sure the pots have drainage holes to allow the excess water to drain from the soil. Though it’s possible to grow succulents in pots without drainage, it’s not recommended.
When the Fairy Castle Cactus is actively growing, you can also add plant food to its soil or water to provide it with the nutrients necessary for growth. This isn’t necessary, but it can help cacti that have used up most of the existing nutrients in their soil. Plant food should not be given during winter when the cactus is dormant.
The Fairy Castle Cactus should be repotted whenever it has outgrown its current container. Depending on the size of the container used, repotting should typically occur about every other year or so.
Propagating a Fairy Castle Cactus is quite simple. There are two popular methods of propagation but is used much more frequently than the other. The reason for this is the time involved. Fairy Castle Cacti are slow-growing, so it’s quite a time commitment to grow them from seeds instead of propagating with cuttings.
The seeds of the Fairy Castle Cactus can be collected from its fruit, but since this plant rarely blooms and is such a slow grower, few gardeners opt for this method of propagation. Seeds may also be found available for purchase online.
If you’re one of the patient few, you should sow your seeds in a well-draining soil formulated for use with cacti. Keep the soil somewhat moist, but not overly wet, until you see seedlings sprout from the soil.
Once the seedlings have breached the soil surface, you can allow the soil to dry out before watering. As with adult cacti, wet soil will lead to rot, so avoid excess moisture at all costs.
During the first year, you may only see a couple of inches of growth from your new cactus, but with patience, your Fairy Castle Cactus will soon produce spires of its own.
For more tips on growing cacti from seeds, read our guide here.
The most common method of Fairy Castle Cactus propagation is with cuttings. Since this cactus typically produces so many branches, collecting cuttings is as simple as cutting or breaking off a few branches.
If you choose to cut the branches, be sure to use sharp and sterile scissors, shears, or a knife to prevent infection and minimize potential damage to your cactus.
After collecting your cuttings, it’s recommended to allow the cuttings to sit in the open air for a few days to allow the cuts to callous. This helps prevent infection by bacteria and fungus once you introduce the cactus cutting to soil.
Before planting, you have the option of dipping the cutting into rooting hormone. This is not a necessary step, but it can help shorten the time between planting and root formation.
Rooting hormone can be found at any nursery, garden center, or online retailer. It’s generally a powder, so most gardeners recommend wetting the base of your cutting before dipping to help the powder stick better.
After your cutting has calloused and you’ve dipped it in rooting hormone if you chose to do so, you’re ready to plant your Fairy Castle Cactus cutting.
During the first few weeks after planting, it’s not really necessary to water your cuttings. They don’t yet have roots, so they can’t really absorb the water anyway. If you’ve used rooting hormone, most manufacturers recommend planting the cutting into moist soil for the best results.
After planting your Fairy Castle Cactus cuttings, it’s important to remember that although this is the “quick” propagation method, you probably won’t see more than 5 to 10 inches of growth during the first year. However, your cuttings may still produce a few branches or “turrets” during this time.
Common Pests and Problems
As mentioned earlier, overwatering is the most common problem with Fairy Castle Cacti. To avoid this problem, it’s essential to make sure the soil has dried out completely before watering again.
This can be accomplished by either using a soil moisture meter or your finger inserted a few inches below the soil’s surface. If it’s dry, it’s time to water, but if it feels moist, you should wait several days before checking again.
Remember, Fairy Castle Cacti are drought-loving succulents that won’t mind waiting a few more days before being water. It’s always best to err on the dry side when it comes to cacti.
Other challenges faced by growers of Fairy Castle Cacti are common cactus pests such as mealybugs and scale. Spider mites and fungus gnats are also possible problems, as are centipedes in some areas.
It should be noted that centipedes can be beneficial to cacti and do not cause harm to plants, but most growers would prefer to keep them out of their indoor cacti collections.
Common pests are typically dealt with by using some combination of high-pressure water, insecticidal soap, or neem oil. For more information on how to deal with pests, read our guide.
Since the life cycle of the most common pests affecting Fairy Castle Cacti is so short, you can go from just a few creepy crawlies on a single plant to a garden-wide infestation in a matter of weeks.
This is why it’s important to check your plants frequently, even if you don’t water them that often. By checking your plants every few days, you can hopefully catch any problems before they become a more serious issue.
You should also practice good plant hygiene by making sure the soil your cacti are planted in isn’t overly moist and you’ve removed all decaying plant material. The cleaner your garden is, the less inviting it is for pests.
It’s also highly recommended to quarantine any new plants you bring home to prevent pests from spreading to your other plants. By keeping new plants separate for at least two weeks, you should have plenty of time to spot any insects crawling around on them.
After all, it’s much easier to treat just a few plants than it is to treat your entire cactus collection. A little preventative care will ensure your Fairy Castle Cactus, as well as any other succulents may have, stay free from pesky pests.