Cactus: plants in the family Cactaceae that are often characterized by having thick, fleshy stems, showy flowers, and lacking in leaves, typically well suited to living in arid habitats.
Basically, the plants that have tried very very hard to discourage being touched, and which humans try very very hard to cultivate with minimal touching.
Depending on the species, they can tolerate full hard frost, or will melt below 50F. Know your species!
Some cacti are borderline tropical in habit, while others need to be kept almost bone dry.
Each species is unique, and the soil blend that they thrive in varies from plant to plant.
Not all cacti want, or need, full sun! Understanding where your plant comes from will help you determine lighting needs.
Cactus Care 101
While each species has different care requirements, there’s a few common threads to how to tend to your cacti.
Most cacti need at least extremely bright indirect light to nearly full sun. There are no cactus species that thrive in the type of shaded, low-light conditions that typical housplants are grown in. While cacti can be grown indoors, they generally need to be in extremely bright locations that receive multiple hours of direct sunlight, even for species that thrive in partial shade conditions outdoors.
Windows filter light, and as a result, you’ll need to be sure that any indoor cacti have access to as much direct sun as possible through their windows. Without this, they will often etoliate and eventually die. If you see your cactus developing long, skinny growth on top that looks wildly different from the lower half, chances are this is etoliation. You cannot correct etoliation once it happens, so the best cure is prevention. Keep your cacti as close to a window as possible, or better yet, fully outdoors when weather permits!
There are few, if any, truly tropical cacti, which means they need to be allowed to dry out between each time you water them. Soggy roots lead to rot.
Water should be tap or filtered, never distilled. Reverse Osmosis, or RO water, is also probably not ideal. You want some minerals and particles to be in the water for your cacti. Extremely hard water may, if anything, be beneficial, as the excess calcium can often be used by the plant to produce spines.
Soft water should be avoided if at all possible, as the salts will slowly kill your cactus without countermeasures being taken.
Outdoors, water more often when it’s hot out (summer), and ensure that the soil around your cactus is thoroughly wet each time you do. Wait until the soil is dry again before you water them more. In hot, dry climates, this can be as often as several times a week during the height of summer. In humid, rainy climates, you may only need to water outdoor cacti every couple weeks. Indoors, water cautiously, and learn how long it takes your soil to dry out. Being in a climate controlled home is less than ideal conditions for a cactus, and not getting as hot or being exposed to full sun often means the cactus should stay dry longer between each watering session.
Soil & Potting
Cacti all need well-draining soil, but different species require different amounts of inorganic medium in their soil. Seek out a quality succulent and cactus blend, and amend with pumice or perlite to make it grittier or better draining as needed.
The pot size needed is almost always smaller than you think. Some species, such as those with large tap roots (some copiapoas or ariocarpus, for example), need a pot that can accomodate their tap roots. Others can get by in laughably shallow pots, such as the melocactus or astrophytum genera. When in doubt, keep the pot small – and if you’re overpotting your cactus, be sure to add more inorganic medium to allow for good drainage throughout. Pockets of soggy soil will rot roots!
A commonly overlooked part of growing cacti is temperature – while many people check on how cold they can get, they seldom think of how hot they may need.
Temperature should be considered in two ways: dormancy period, and growth period.
Pretty much all cacti are dormant in winter, when it’s cold. “Cold” for a cactus may be at 60F, or it may be at 40F – that part varies heavily by species. Many cacti can tolerate temperatures below freezing for short periods, but it is a small portion that can tolerate snow, and even fewer that can do so for more than a few days at a time. Short daylight hours combined with decreasing temperatures usually tell cacti it’s time to rest for winter, and during this period, they should receive little to no water. When kept dry, a surprising number of cacti can tolerate very cold temperatures for short periods (i.e. 2 – 4 hours at a time).
On the other end, during growth periods, most cacti prefer and even need warm weather. This means temperatures in the high 70s or, preferably, 80 – 90 degree range. Your typical home with air conditioning rarely gets that hot! For robust, healthy growth, strongly consider keeping your cacti outdoors or on a sheltered patio (so they don’t get too much rain) when the weather is warm enough. Some species, such as those in the genus gymnocalycium, thrive on extreme heat and will accept large quantities of water during their growth season. Knowing your cactus species’ requirements will help you significantly in keeping them healthy and robust enough to thrive no matter the conditions!
You really don’t need to fertilize most cacti, especially within the first year of freshly repotting them. If you really must, a balanced (1:1:1) ratio fertilizer at 1/4 – 1/2 strength once or twice during the growing season is plenty.
You can use a succulent/cactus specific fertilizer at a dilute strength instead if you prefer. These are often higher in potassium and/or phosphorus, and can contain additional calcium as well.
You genuinely do not need to fertilize more than a couple times during the height of growing season, and feeding too often can cause problems that eventually lead to your cactus dying. When in doubt, skip a feed.
A small genus of cacti with only 5 species:
- Astrophytum asterias
- Astrophytum capricorne
- Astrophytum caput-medusae
- Astrophytum myriostigma
- Astrophytum ornatum
While only a few species exist in the genus, all except the most recently discovered (caput-medusae) have numerous cultivars. These carefully cultivated varieties can be more delicate than their “wild-type” cousins, but all are beautiful and rewarding to keep.
About the Astrophytum Genus
All cacti in the genus, in their wild form, come from the Chihuahuan desert in Mexico (north/east), ranging up into southern Texas.
The entire genus is distinct in having fuzzy white trichomes (bumps) on their epidermis, or skin. Some varieties have been selectively bred to significantly reduce this fuzziness, but it is distinct in the species. All plants bloom yellow, with some having a red-centered flower, and certain recent cultivars showing pink blooms.
They all produce dry, fuzzy seed pods with relatively large seeds that are generally easy to germinate.
Astrophytum caput-medusae - coming soon!
A genus with a fan club! Those who love copiapoa tend to become enormously dedicated to their favorite genus. While there are dozens of species, the entire genus is limited to Northern Chile.
Hardy and Slow to Grow
All copiapoas are generally globose or cylindrical-globose in shape, extremely slow growing, and develop a wooly top. Nearly all of them bloom with bright yellow flowers.
All cacti in the genus originate in Northern Chile. The stark deserts they exist in get little to no measurable rainfall, with most moisture for the plants coming from fogs rolling in from the coast.
While they grow in extreme conditions in the wild, cultivated plants are generally very forgiving. They stay small and manageable, which may be a reason they are so popular with collectors.
Copiapoa montana (?)
A historically large genus, many modern collectors view it as having only 6 species currently. I’ll be lumping all cacti that were previously considered as Echinocactus in here, but will note their updated scientific name where possible.
Wide Ranging...at one point.
The original description of the genus included plants that ranged from all over North & South America, were generally globe-shaped and didn’t fit in with either the Cereus or Melocactus genus.
Echinocactus, Ferocactus, Echinocereus…
I have no where close to the entire historical genus of Echinocactus, and wouldn’t dream of trying to catalog them all this way. For now, I’ll list them below – to see more details about their updated genus, click through.
These cacti all share an affinity for nearly full sun, sparse winter watering, and plenty of heat. They’re all globe-shaped, and tend to produce yellow or pink flowers. I’m grouping all of my barrel shaped cacti here in true cactus sorting fashion.
Now Echinocereus gentryi
Echinocactus ingens (coming soon)
Mine may actually be E. ingens; now Ferocactus emoryi
Echinocereus rigidissimius var. rubrispinus
Echinopsis var. "Rainbow Bursts"
Echinopsis var. "LA"
The entire genus are all “chin cacti” which I think is probably the silliest name for plants ever. They’re generally small, subtle cacti that haven’t quite taken off in mainstream cultivation yet.
A famous sibling
There’s one Gymnocalycium you’ve probably seen or heard of, and it’s the purple moon cactus. Various types of albino types are commonly seen available as grafted specimens at home depot, grocery stores, and more. The genus has so much more to offer!
The entire genus consists of small, globular cacti that don’t quite have super distinct ribs. They often have small or few spines, and flower extremely easily – but the blooms only open fully in extreme heat and full sun. They range throughout South/East South America, and range in their preferred environment and elevation.