Acanthocalycium cactus (a-kanth-oh-ka-LEE-see-um) is a genus of decorative cactus species known for their colorful abundant blooms.
The genus belongs to the family Cactaceae and native to the humid warmth northern region of Argentina, South America primarily in the province of Cordoba.
Compared to other cacti species within the family, the genus Acanthocalycium is easily identifiable from the large areolas with spines.
Found abundantly in Argentina, the genus name comes from Greek, translating to mean ‘prickly buds’ where ‘akantha’ means prickly and ‘kalyx’ means buds.
This is a reference to the sharp spines the floral tubes possess.
Common names include:
- Barbed wire cactus
- Sword pear
- Triangle cactus
Acanthocalycium Cactus Care
Size & Growth
The Acanthocalycium species are known for their flowers. These cacti begin as round or cylindrical.
Eventually, as they mature, they take on a more elongated and become more elliptical.
The stems of the Acanthocalycium species have approximately 19-20 ribs that grow spiny areolas.
The cactus itself has a greenish-gray color with nuances fading towards yellow. The spines on the ribs are darker at the base and almost silver towards the tip.
Depending on the species and Acanthocalycium variety you choose, the cactus can grow up to 4″ to 6″ inches in length and 4-6″ inches diameter.
The cacti may also take up to 3 years to reach full maturity.
Flowering and Fragrance
As mentioned previously, the Acanthocalycium genus is known for its blooms. The cacti begin blooming in the spring and continue to do so until summer.
The noticeable squamous floral tubes grow on top of the cacti. It is from these floral tubes or spiny chalices the flower blooms.
The flower itself is pretty large and bell or funnel-shaped.
As for size, it is 2″ inches in length and up to 1.6 inches in diameter.
The flower color depends on the species and varies from red, pink, purple or yellow.
Light & Temperature
Acanthocalycium, like many other cacti, loves the sun. Place them in an area that receives full sun throughout the day, in an airy environment.
Place them in partial shade in the hotter months. They do well in USDA hardiness zones 8b to 11.
The minimum suitable temperature for the Acanthocalycium plants is 45° degrees Fahrenheit.
If the temperature drops below 45 degrees Fahrenheit, it can hinder the cactus’s growth.
If you are in a cold location, make sure your Acanthocalycium plant is in a sheltered environment.
Watering and Feeding
The Acanthocalycium genus is drought-tolerant, making them suitable for xeriscaping.
Acanthocalycium plants have moderate watering needs and need watering every three to four days in the summer.
However, make sure not to overwater as it can damage the roots.
In the winter time, reduce watering to once a week or longer. Again, avoid overwatering.
Wait until the soil is almost completely dry before watering it again.
Use a balanced fertilizer and feed the cactus at least once a month during the growing season of May to October.
Soil & Transplanting
Acanthocalycium species thrives in well-drained soil.
Repotting is best done at the beginning of the growing season (spring) or in the summer.
Repot when the soil is dry.
Gently tap on the pot to loosen up the roots and then gently remove the pot.
Remove old soil and dead roots with a gentle hand. Place the plant back in a new pot and backfill with potting soil.
Leave the plant dry for a week and then water lightly to avoid root rot.
Grooming and Maintenance
Acanthocalycium is a low maintenance cactus.
The only thing you need to be careful of is not to overwater and use well-drained soil.
Propagating Acanthocalycium
Propagate Acanthocalycium cactus from seed.
Growing cactus from seed can be exciting, as you watch the tiny seedlings change their appearance rapidly.
Watching the changes is fun and a learning experience as you sow seeds and grow mature plants.
Seed Sowing Containers Must Be Clean
A shallow clay or flower pot or even a plastic tray will work as a seed planting container.
Whatever type of container selected for planting seed – IT MUST be thoroughly clean.
To clean and disinfect your pots, clay or plastic follow this step by step process:
The easiest way to clean and sterilize pots is to dip them in bleach solution.
- 9 parts water
- 1 part bleach
- Let pots soak for 10 minutes.
- Then put the pots in a dish soap and water rinse for 10 minutes
- Allow pots to dry
Once the pots have dried, cover the bottom holes and fill the container with a cactus soil.
Do not press or firm the soil too much. Instead settle the soil by tapping the container on a hard surface a few times.
Leave a distance of about ½” inch from the soil surface to the top edge of the pot.
This allows room to lay a sheet of glass on top.
Spread the seed as evenly as possible and press the seed in lightly with a small piece of wood.
This eliminates the need for sifting the soil over the fine seed.
NOTE: Add some sand to the seed to help distribute the seed evenly
Germination Temperatures
Acanthocalycium seeds germinate best at a steady temperature of around 80°degrees Fahrenheit.
Successful germination is possible at temperatures around 70° degrees Fahrenheit, especially if temperatures vary between 70° – 85° degrees Fahrenheit.
Mini greenhouses are also a great way to sow and grow cactus seed.
Water Carefully
Cactus seed can easily be washed away when watering. It is a good idea to put the seed tray or pot in a shallow bowl of water.
Like sub-irrigation (SIPs), the soil wicks up the water from the bottom.
The pot of seeds should not be in direct sun but in a bright spot.
Be careful not allow the soil dry out while the seeds are germinating. Seeds sometimes begin to sprout after as little as 10 – 14 days.
Once sprouted remove the glass sheet or the lid of the mini-greenhouse.
The young plants need circulating air and light and less moisture to prevent rotting.
Learn more on starting cactus propagation in our article on – How To Propagate Cactus.
Acanthocalycium Pest or Disease Problems
Acanthocalycium is susceptible to root rot when left in water for prolonged periods in a humid climate.
As for pests, Acanthocalycium cacti are vulnerable to attacks from aphids, mealy bugs, and whitefly.
If you see an infestation, treat it with the least toxic option as early as possible to avoid the situation from worsening.
Suggested Acanthocalycium Uses
The various species of Acanthocalycium are best known for their pretty, colorful blossoms.
Hence, they make excellent decorative plants and perfect for a window garden.