A columnar cactus, the tall, upright kind such as San Pedro (a Trichocereus), can live indoors all year, outdoors all year, or outside for the warm months and inside for the cold ones.
The short version
- A cactus gets less light indoors than outdoors, even in a bright window. It grows more slowly and needs less water.
- Indoors, give it your sunniest window, usually a south-facing or west-facing one, and keep it close to the glass.
- If the window gives less than 4 hours of direct sun a day, add an ordinary white grow light.
- In winter, keep it cool, bright and nearly dry so it rests. If you have no cool spot, keep it in your brightest window or with a grow light.
- A plant that has lived indoors will sunburn if it goes straight into outdoor sun. Start it in shade and add sun over a few weeks.
- Bring a potted plant in before the first frost, with its potting mix dry and the plant checked for pests.
Which arrangement fits you
- Outdoors all year. This suits places where winter nights rarely fall below the high 20s F and winters are not wet.
- Outdoors in summer, indoors in winter. Choose this where winters are colder than that, or cold and wet together. The plant has to be in a pot you can lift or wheel.
- Indoors all year. This works with a window that gets at least 4 hours of direct sun, a grow light, or both. Growth will be slower than it would be outside.
If you are not sure about your winter lows, start with how to read your climate and your own spot.
Light and water indoors
Even the brightest spot in a house gets only a fraction of the light of a shady spot outdoors. Light also falls off quickly with distance, so a plant 3 feet back from the glass gets less than one on the sill.
Choose the window that gets direct sun for the most hours. In the northern half of the world that is a south-facing window first, then a west-facing one. Aim for at least 4 hours of direct sun on the plant each day, and stand the pot close to the glass. An insect screen, a curtain, a roof overhang or a tree outside each cut the light further.
A cactus in a window grows more slowly than it would outdoors and uses less water. Let the potting mix (the soil in the pot) dry all the way to the bottom between waterings, and expect longer gaps than the same plant would need outside.
If your brightest window gives the plant less than 4 hours of direct sun, plan on a grow light or a summer outdoors.
Grow lights
A grow light is a lamp that adds to the light from a window. How much light reaches the plant matters most, and an ordinary white lamp gives the colors a plant needs.
- Type. A white LED grow light or a white fluorescent tube suits a cactus. LEDs use less electricity, last longer and give off little heat.
- Distance. Fluorescent tubes go 6 to 12 inches above the plant.
- Hours. Run the light 14 to 16 hours a day and no more than 16. Plants need a dark period, and a plug-in timer keeps the schedule for you.
Let the plant be your gauge. If new growth at the tip comes in thinner and paler than the stem below it, the plant is stretching for light and needs more.
Winter indoors
Winter light through a window is weak. A cactus that keeps growing in it makes thin, pale, stretched growth, which is called etiolation. A stretched section may never fill back out, though later growth made in good light will come in at normal width, giving your cactus a somewhat wonky look.
A cool, dry rest stops the plant growing until the light returns.
- Cool. Keep it at about 45 to 55 F. An unheated room or an enclosed porch will do, as long as it stays above freezing.
- Bright. Give it the best light you have.
- Nearly dry. Water only if the stem starts to shrivel, meaning the skin wrinkles. For most plants that is a light watering every few weeks, and in a cold room it can be none at all.
A cool, dry rest with good light also helps many cacti flower the following season.
If you have no cool spot, keep the plant in your brightest window and add a grow light.
Moving out in spring
A cactus that has spent months indoors has no sun-hardened side. Put straight into outdoor sun, it burns. Sunburn shows as discolored patches on the side facing the sun, and on a cactus the damage is permanent.
- Wait for the weather. Move the plant out after the last frost, once the weather has warmed.
- Start in shade. For the first couple of weeks, give it a place that is bright but gets no direct sun, such as under a tree or a patio cover.
- Add sun in steps. Move it to a sunnier place a little at a time. While it adjusts, keep it out of the hot sun between about 11 a.m. and 3 p.m.
- Take it over a few weeks. Let the plant set the pace. If the sunny side starts to discolor, move it back to a shadier place and go more slowly.
- Water more. A pot dries faster outdoors, so check the mix more often than you did inside.
Do this each time the plant moves from indoors to outdoor sun.
A tall plant in a pot can blow over, so use a heavy, wide-based pot. In the hottest desert climates, a cactus may need shade cloth through the summer.
Moving in for autumn
Move a potted cactus indoors before the first frost in the forecast. The guide for San Pedro is to start protecting at 28 to 30 F, and earlier for pots and in wet winters. For a plant in a pot, protecting means bringing it inside, so the first frost forecast is your signal.
- Dry it off first. As nights cool in early autumn, cut back watering and stop fertilizing, so the plant goes into winter dry and resting. A cactus pushed to grow in autumn is more easily damaged by cold.
- Check for pests. Look over the whole stem and the base, then slide the plant out of its pot and check for anything that has crawled in through the drainage holes. White, cottony insects are mealybugs. Small bumps clustered or lined up along the stem are scale. Wipe off either one with a cotton swab dipped in rubbing alcohol.
- Keep it apart. Stand it away from your other houseplants for 3 to 4 weeks and check it again during that time.
- Put it in its cool, bright winter spot.
When a column outgrows the window
A fast-growing, thick column such as San Pedro will in time reach the top of a window. At that point it needs a summer outdoors, a taller indoor space, or its top cut off and rooted as a new plant. See how to root a cactus cutting.
Sources
Lighting for Indoor Plants. University of Maryland Extension, 2023. https://extension.umd.edu/resource/lighting-indoor-plants
Lighting for indoor plants and starting seeds. University of Minnesota Extension. https://extension.umn.edu/planting-and-growing-guides/lighting-indoor-plants
Cacti and succulents. University of Minnesota Extension. https://extension.umn.edu/houseplants/cacti-and-succulents
Growing Indoor Plants with Success. Bulletin 1318, University of Georgia Cooperative Extension, reviewed 2022. https://fieldreport.caes.uga.edu/wp-content/uploads/2025/08/B-1318_6.pdf
Indoor Cacti. Factsheet HGIC 1502, Clemson University Cooperative Extension Home and Garden Information Center, 2015. https://hgic.clemson.edu/factsheet/indoor-cacti/
Moving Houseplants Indoors & Outdoors. Factsheet HGIC 1454, Clemson University Cooperative Extension Home and Garden Information Center, 2023. https://hgic.clemson.edu/factsheet/indoor-plants-moving-plants-indoors-outdoors/
How to grow houseplant cacti and succulents. Royal Horticultural Society. https://www.rhs.org.uk/plants/types/cacti-succulents/houseplants/growing-guide
Moving Indoor Plants Outside for the Summer. Iowa State University Extension and Outreach. https://yardandgarden.extension.iastate.edu/how-to/moving-indoor-plants-outside-summer
How and when do I bring my houseplants back indoors before winter? Iowa State University Extension and Outreach. https://yardandgarden.extension.iastate.edu/faq/how-and-when-do-i-bring-my-houseplants-back-indoors-winter
Diagnosing Houseplant Problems Caused by Insect Pests. Iowa State University Extension and Outreach. https://yardandgarden.extension.iastate.edu/how-to/diagnosing-houseplant-problems-caused-insect-pests
Cactus, Agave, Yucca and Ocotillo. University of Arizona Cooperative Extension, 2009. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1225.pdf
Six Tips To Care For Your Plants This Summer. Desert Botanical Garden, 2026. https://dbg.org/six-tips-to-care-for-your-plants-this-summer/