Choose a cactus you love. Then check that it fits the place you have for it. 4 things about the plant decide that: the cold it takes, the size it reaches, its spines and the light it needs.
Find your situation below. More than one can apply. To read your own climate and spot, see growing cactus for your conditions.
The short version
- Frost: find your USDA hardiness zone and compare it with the cold the plant takes.
- Wet winters: look for a plant you can keep dry.
- Pots: check mature spread as well as height.
- Indoors: you need an unshaded south-facing window and a plant that stays small.
- Hot desert summers: placement and shade matter more than the plant.
- Near people and pets: look for few, short spines.
- Height: look for a columnar cactus and check its cold tolerance.
- Flowers: check the direct sun the plant needs to bloom.
- If the spot cannot work, pick another spot or wait.
Frost most winters
Look at cold tolerance, the lowest temperature the plant comes through, and compare it with your coldest nights. In the United States, your USDA hardiness zone gives you those: each zone is a 10-degree band of the average coldest temperature of the year. Look yours up by zip code on the USDA map.
San Pedro (a Trichocereus) is a tall, upright column. Torch cactus hybrids are low, clumping plants grown for their flowers, and they take more cold than San Pedro.
For San Pedro: Start protecting at 28 to 30 F, earlier for pots and in wet winters. Some growers report that their mature, well-established plants came through brief dips into the low 20s F unharmed. It is always wise to stay on the conservative side. Established means growing in place for at least a full season. Earlier means at a warmer temperature.
Protecting means covering the plant on cold nights with frost cloth or a fabric such as burlap, never plastic, and taking the cover off when the day warms. A pot can be moved under shelter or indoors.
If your coldest nights fall below the low 20s F, choose a plant that takes more cold, or one for a pot that winters under cover.
Wet winters
A cactus that goes into winter dry stands cold better than one kept wet. Wet soil is also more likely to cause rot in the cool season.
Look for a plant you can keep dry. The trait to check is mature size: a plant small enough to lift in its pot can be moved out of the rain. Judge its mature height and spread against the covered space you have.
In the ground, a cactus needs soil that water runs through quickly, and a drier place helps, such as the strip under an eave. Blue myrtle, a blue-gray branching cactus, is prone to root rot in damp, poorly drained soil.
A pot on a patio or balcony
Check mature spread as well as height. The stems of a torch cactus hybrid grow in a cluster to about 2 feet tall and then sprawl outward, so the clump ends up wide. A mature one needs a pot at least 14 inches wide.
Roots in a pot are more exposed to cold than roots in the ground, so a potted plant needs protecting at a warmer temperature.
A bright window indoors
A bright window gives a cactus less light than it would get outside. Indoors, a cactus needs direct sun for 4 to 6 hours a day, which means an unshaded south-facing window or a sunroom. With less, a plant stretches toward the light, grows thin and leans. If you have no such window, do not buy for that spot. Choose another place or wait.
Look for a mature height and spread that fit the space at the window, and for few spines.
Hot desert summers
Cacti need strong light. Many take direct sun for most of the day once they are used to it, and in hot desert climates most do better with some shade.
Here placement and shade matter more than which plant you choose. Look for a spot with afternoon shade, or plan on shade cloth rated to block 30% to 50% of the sun, left on all summer. Many growers in hot climates give afternoon shade once temperatures climb past the mid 90s F.
Paths, children or pets nearby
Look at how many spines the plant has and how long they are. San Pedro often has no spines, and where they grow they are few and under 1 inch long. Peruvian torch is another tall, upright column, not a torch hybrid. Its older growth carries clusters of spines with 3 or 4 stout ones about 2 inches long.
Plant far enough back that the cactus at its mature spread still clears the path.
You want height
Look for a columnar cactus, which grows as an upright stem many times taller than it is wide. In its native Andes, San Pedro reaches 6.5 to 13 feet (2 to 4 m) tall. It often branches from the base, so an old plant can become a stand of columns. Blue myrtle branches into a candelabra, a trunk with many upturned arms. In the ground in a warm climate it can reach 15 feet tall and spread as wide or wider.
A tall plant in the ground cannot be moved, so check its cold tolerance first.
You want flowers
Compare the direct sun the plant needs to flower with the hours your spot gets.
The flowers of torch cactus hybrids are large and come in red, orange, yellow, pink or white. On a big clump, 50 or more open at once on 2 or 3 days a year, with 1 or 2 at a time on 5 to 30 more days. They will not flower with less than 4 to 5 hours of direct sun a day.
Before you buy
Check the cold hardiness and size given for the plant you are considering. If they do not match your spot, choose a different spot or a different plant.
Sources
2023 USDA Plant Hardiness Zone Map. United States Department of Agriculture, Agricultural Research Service. https://planthardiness.ars.usda.gov/
Identity and neotypification of Cereus macrogonus, the type species of the genus Trichocereus (Cactaceae). Sofía Albesiano and Roberto Kiesling, Haseltonia 17: 24-34, 2012. https://cactusconservation.org/wp-content/uploads/2020/03/Albesiano_Kiesling_2012_Haseltonia_17_24-34.pdf
Arizona-Sonora Desert Museum Plant Care Information: Torch Cacti, Trichocereus hybrids. Arizona-Sonora Desert Museum. https://www.desertmuseum.org/visit/sheets/TrichoX.pdf
Echinopsis huascha. Arizona State University. https://www.asu.edu/lib/camartin/plants/Plant%20html%20files/echinopsishuascha.html
Myrtillocactus geometrizans. Arizona State University. https://www.asu.edu/lib/camartin/plants/Plant%20html%20files/myrtillocactusgeometrizans.html
Frost Freeze. Zann Wilson, SaddleBrooke Master Gardeners, University of Arizona Cooperative Extension. https://extension.arizona.edu/sites/extension.arizona.edu/files/attachment/Frost-freeze.%20prelim.%20SBMG%20docx.pdf
Cactus, Agave, Yucca and Ocotillo. University of Arizona Cooperative Extension, 2009. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1225.pdf
Lighting for Indoor Plants. University of Maryland Extension. https://extension.umd.edu/resource/lighting-indoor-plants
Six Tips To Care For Your Plants This Summer. Desert Botanical Garden. https://dbg.org/six-tips-to-care-for-your-plants-this-summer/