Though the term "cereus" once referred to any columnar species of cactus with an elongated body, today Cereus is a more specific genus of about fifty species and many of the cacti that were once considered Cereus cacti are now in other genera. Today, Cereus cacti are distinguished by their columnar growth habit, with ribs that spines protrude from. Since the genus was formed by removing other species from it, it includes some diversity – many species are classified as Cereus simply because they were not given any other genus.
This leads to some cacti being included that don't fit the typical Cereus profile, like the thin C. albicaulis and C. insularis. Nonetheless, there is a basic template that most – but not all – Cereus cacti fit: they're large, tree-like cacti with defined ribs and aureoles that require slightly richer, more moist soil than a typical cactus. Atypically for cacti, Cereus should not experience drought during their growing season in the summer, although they can tolerate lower water supply in winter. They produce long, fleshy, edible fruits that are generally red. These cacti are good for a succulent or rock garden where they have room to grow because they can be fairly large; for instance, the Hedge Cactus, or C. peruvianus (C. repandus), grows to about ten feet tall and its monstrose form is popular for its idiosyncratic, divided ribs. Most of these cacti are too large to grow inside, but younger specimens can be kept inside until they mature, and most plants in the genus are slow-growing. If you do keep Cereus inside in containers before moving them outside, be careful of their sharp spines when moving them.
Light: Like all cacti, give them lots of direct sunlight, especially during the summer.
Water: Cereus plants need slightly more water than most other cacti, and their soil should usually be kept moist during the growing season.
Temperature: Though hot temperatures are best, most of these are hardy plants that can tolerate down to about 20 degrees Fahrenheit (-7 degrees Celsius).
Soil: Well-drained soil is best, and most Cereus perform well in a soil that contains some organic material. Some recommend avoiding a soil that contains sphagnum moss, though – it can make the cactus vulnerable to root rot.
Fertilizer: They should be fertilized during their growing season in the summer with a good cactus fertilizer.
Cereus cacti propagate quite easily from cuttings; simply sever a branch and replant in moist, well-drained soil. It helps to allow the cut end dry out and harden before you replant it; this makes it easier for the new cactus to form roots.
It may become necessary to repot your Cereus if it outgrows its container. If so, make sure the soil is dry and then remove the pot. Knock away old soil and prune away any rotted or dead roots, then replace it in a new pot and backfill with new soil. Make sure not to overwater cacti planted in new pots, as this can lead to root rot – it should be left dry for about a week and then watered lightly.
Like most cacti, Cereus are fairly low-maintenance and hardy. Make sure they receive enough water without becoming waterlogged, especially during the summer, and fertilize them for best results. If the roots have become black or overly soft, the cactus could be experiencing root rot – cut away the affected parts and replant. Most gardeners interested in cacti should be able to cultivate these without much problem.
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