Growing cactus for your conditions

A cactus on a dry patio in Phoenix and the same cactus in a pot in Seattle need different care. What keeps one healthy can kill the other.

Start by reading your own conditions: your climate, and the spot where the plant will live.

The short version

  1. Your climate comes down to 4 things: how cold your winters get, how wet they are, how strong your sun is, and how hot your summers run.
  2. Wet cold is harder on a cactus than dry cold.
  3. How long a freeze lasts matters as well as how low it goes.
  4. Cacti need strong light. In hot desert climates most do better with some shade.
  5. Your own spot can be kinder or harsher than your climate. Walls, eaves, slopes and pots all change what the plant gets.
  6. Treat any cold-hardiness figure, the lowest temperature a plant is said to survive, as a starting point, and adjust it to your garden.

Why your conditions matter

Columnar cacti, the tall, upright kinds such as San Pedro, are grown from foggy coasts to hot desert, in the ground, in pots and on windowsills. Each of those settings calls for different care.

Cold-hardiness figures for these plants are growers' experience, each gathered in one garden under its own conditions. They do not come from controlled trials. So the figures vary from grower to grower, and your own conditions decide how far any one of them applies to you.

Cold: how low, how wet, how long

Cold is one of the conditions most likely to kill an otherwise healthy cactus. How low it goes, how wet it is and how long it lasts all count.

How low. Start with the coldest night you can expect in a normal winter. In the United States, your USDA hardiness zone is built on that: the average coldest temperature of the year where you live. You can look yours up by zip code on the USDA map. Use it as a first filter. Wet and duration decide the rest.

How wet. A cactus that goes into winter dry stands cold better than one that is kept wet. Cutting back water as winter approaches is the standard way to harden a cactus, meaning to toughen it, for the cold. Wet soil is also more likely to cause rot in the cool season, when the plant is resting and not growing. If most of your rain falls in winter, your plan has to include keeping the plant dry: a gritty, fast-draining soil, a pot you can move, or cover from the rain.

How long. A brief freeze before dawn often leaves only cosmetic damage that the plant grows out of. Long freezes, and very cold ones, do serious harm. Even the saguaros of the Arizona desert suffer catastrophic damage when the temperature falls to about 17 to 22 F and stays there for 15 to 20 hours. If your cold snaps last days, not hours, plan for more protection than your lowest temperature suggests.

On many columnar cacti the growing tip at the top of the stem is the most cold-sensitive part, so cover the tips first on the coldest nights.

Sun: strength and heat

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.

Sun becomes too much in 2 cases.

A sudden change. A plant grown in shade or kept indoors is not used to direct sun, and it can burn if it is moved straight into it. The same goes for a plant that has spent days in a shipping box. Start such a plant in light shade and move it into more sun a little at a time, over a period of weeks.

Extreme heat with the sun. In the hot desert country around Phoenix, cacti and other succulents benefit from shade cloth kept on through the summer. Shade cloth is a woven fabric rated by how much sun it blocks, and 30% to 50% is the useful range. Many growers in very hot climates give afternoon shade once temperatures climb past the mid 90s F.

Where the plant sits changes how much sun it takes. A west-facing spot, which gets the afternoon sun, is hotter and drier than other exposures. A wall or paving that reflects heat and light at the plant can burn it.

Your spot within your climate

Within a few steps, your garden has places that are warmer, colder, wetter and drier than the average for your area. Choosing the right one can matter as much as where you live.

  • Walls. A wall that faces the afternoon sun stores heat and gives it back at night. That is a help where winters are cold and a hazard where summers are hot.
  • Eaves and overhangs. An eave blocks rain, so the ground beneath it stays drier. In a wet-winter climate that strip can be a good place for a cactus.
  • Low spots. Cold air pools in hollows and at the bottom of slopes, so those places freeze first.
  • Slopes. Water runs off a slope, so soil near the top dries faster. The bottom collects water as well as cold air.
  • Pots. Roots in a pot are more exposed to cold than roots in the ground. In exchange, a pot can be moved: out of the rain, against a warm wall, or indoors for the winter.
  • Indoors. Even a bright window gives a cactus much less light than it would get outside. An indoor plant grows more slowly, and it usually needs less water.

5 questions to answer before you start

  1. How cold does it get in a normal winter?
  2. Are your winters wet or dry?
  3. When it freezes, does it last hours or days?
  4. How strong and how hot is your summer sun?
  5. Where will the plant live: in a pot or in the ground, and what is around it?

Find the cases closest to yours. More than one can apply.

  • Dry winters with little or no frost. You have the most freedom. Many growers in these climates keep columnar cacti outdoors all year, in the ground or in pots.
  • Dry winters with frost most years. Keep the plant dry going into winter, cover the growing tips on the coldest nights, and expect to move pots under a roof or indoors when a hard freeze is forecast.
  • Rainy winters, with or without frost. Keeping the plant dry is the main job. Use a gritty, fast-draining soil, grow in pots you can move, or plant where rain does not reach.
  • Freezes that last days. Grow in pots and bring them indoors, or into a garage or greenhouse that stays above freezing, for the winter.
  • Very hot, bright summers. Give afternoon shade or shade cloth in summer, and bring new plants up to the sun slowly.
  • Indoors all year. Give the plant the brightest spot you have, water less than you would outside, and expect slower growth.

Cold hardiness and watering needs vary by plant. You will find both on each plant's product page.

Keep reading

Once you know your conditions, these guides take each part of growing in turn.

Sources

2023 USDA Plant Hardiness Zone Map. United States Department of Agriculture, Agricultural Research Service. https://planthardiness.ars.usda.gov/

Cactus, Agave, Yucca and Ocotillo. University of Arizona Cooperative Extension, 2009. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1225.pdf

Problems and Pests of Agave, Aloe, Cactus and Yucca. University of Arizona Cooperative Extension. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1399.pdf

Saguaro Problems, Pests and Disease. University of Arizona Cooperative Extension, 2021. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1962-2021.pdf

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

Six Tips to Care for Your Plants This Summer. Desert Botanical Garden. https://dbg.org/six-tips-to-care-for-your-plants-this-summer/

Garden Site Microclimate Evaluation Form. UC Marin Master Gardeners, University of California Agriculture and Natural Resources. https://ccfruitandnuts.ucanr.edu/sites/default/files/2010-08/47782.pdf

Lighting for Indoor Plants. University of Maryland Extension. https://extension.umd.edu/resource/lighting-indoor-plants

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