Light
Full Sun
Requires full, direct sunlight; partial shade leads to weak growth.
Reference image 
Reference image Cactus hexagonus
Six-angled Column Cactus
Overview
Cactus hexagonus (currently widely accepted as Cereus hexagonus) is a monumental, columnar cactus species belonging to the Cactaceae family. Known for its rapid growth and distinct ribbed structure, it is a prominent feature in arid landscapes and large indoor collections 1.
Taxonomy and Naming
Originally described by Carl Linnaeus under the name Cactus hexagonus, this species was later combined into the genus Cereus 2. The specific epithet 'hexagonus' refers to the common six-angled or six-ribbed cross-section of its vertical stems.
Distribution and Habitat
Native to South America, particularly southeastern Brazil (including Minas Gerais, Rio de Janeiro, São Paulo, and Espírito Santo), it thrives in rocky outcrops, dry shrublands, and open, sun-drenched savannahs 3.
Appearance
The stems are bluish-green when young, transitioning to a dull green as they mature, characterized by 6 to 7 deep ribs. Large, nocturnal white flowers bloom during the summer nights, designed to attract nocturnal pollinators like bats and moths 1.
Cultivation and Care
This species demands full sun and exceptionally well-draining soil. Water thoroughly during the active growing season, allowing the potting medium to dry out completely between waterings. During winter, reduce watering to a minimum to mimic dry seasonal cycles.
Common Cultivation Errors
Overwatering and the use of heavy, moisture-retaining soils are the leading causes of root rot. Inadequate light exposure leads to etiolation, resulting in weak, pale, and thin stem growth 2.
Bibliography
References
Watering
10-30 Days
Water only when the soil is dry. Keep completely dry in winter.
Soil
Well-drained, sandy and pumice-based cactus soil mix
Use a porous, sandy potting mix with high gravel or pumice content.
Safety
Pet Friendly
Sharp spines can cause injury; handle with heavy gloves.
Difficulty
Easy
Highly resilient and very easy to care for, provided it is not overwatered.
Native Habitat
Brazil
Inhabits the dry rocky slopes and scrubby savannahs of southeastern Brazil, where it grows as a towering columnar element of the local vegetation.
Frequently Asked Questions
Can Cactus hexagonus be grown indoors?
Yes, but it requires a very bright spot, such as a south-facing window, receiving at least 6 hours of direct sunlight daily.
How often should I water it?
Water when the soil is completely dry in summer (about every 10 days). In winter, suspend watering almost entirely (once a month or none).
What potting soil should I use?
Choose a specialized cactus mix with excellent drainage, containing high amounts of pumice, perlite, and coarse sand.
Is it toxic to pets?
It is non-toxic, but its sharp, rigid spines pose a physical injury hazard to pets and children.
How fast does Cactus hexagonus grow?
It is relatively fast-growing for a cactus, potentially adding 20-30 cm of height per year under optimal warm and sunny conditions.
How can I encourage it to bloom?
To trigger blooming, provide a cool and dry winter rest period followed by full, direct summer sun.
Can I leave it outside in winter?
It is frost-sensitive. Move it indoors when temperatures drop below 5°C (41°F).
Why is the base of my cactus turning yellow and soft?
This is usually a sign of root rot caused by overwatering. Stop watering immediately, and propagate the healthy top section if necessary.
When should I repot it?
Repot in spring, usually every 2-3 years, or when the root system has completely filled the current pot.
Why is my cactus growing thin and pale?
This is etiolation, caused by insufficient light. Move your plant to a much sunnier location.