Cactus Plant Care: Light, Watering, Soil and Winter Rest

Put it in your sunniest window, let the soil dry out completely before you water again, water even less in winter, and feed it once or twice a year. University of Minnesota Extension's instructions are a bright, sunny window, a mix of one part potting soil and one part coarse sand, and soil allowed to dry out completely between waterings.

Most indoor cacti die from two things: too little light and too much water. Joy Us Garden, which grows cacti indoors, says plainly that they are not low-light plants and need at least six hours of bright light a day. The rest of this page gives the numbers from each source, including where they differ.

This page is for desert cacti. A Christmas cactus is a forest cactus that wants moist soil and indirect light; see our Christmas cactus care guide.

• How much. At least six hours of bright light a day (Joy Us Garden); Planet Desert gives six to eight hours for indoor cacti and at least six hours of direct sun outdoors.
• Which window. South- or west-facing (Planet Desert). Joy Us Garden moves its cacti to the brightest spot in winter and turns them every two months so they grow evenly, but warns that a cactus pressed against hot glass in strong sun can burn.
• Grow lights. UMN Extension uses cool white fluorescent tubes, or daylight and natural white tubes together, 6 to 12 inches above the plants for 14 to 16 hours a day.

A cactus that grows tall, thin and pale toward the window is stretching for light, which Planet Desert calls etiolation. The stretched part will not thicken again, so move the plant to more light as soon as you see it.

Only when the soil has dried out completely, which in practice means every one to three weeks in summer and much less in winter. The sources give different intervals, so treat these as ranges and check the soil:

• Spring and summer. Every 1 to 2 weeks (Planet Desert); every 2 to 3 weeks (Joy Us Garden).
• Autumn. Every 3 to 4 weeks as growth slows (Planet Desert).
• Winter. Every 4 to 6 weeks (Planet Desert); every 2 to 4 weeks from November to February (Joy Us Garden). UMN Extension says to water sparingly, just enough to stop the plant shrinking and withering.

How to water matters as much as how often. UMN's method is to water until it flows out of the drainage holes, then discard the excess after a few minutes. Do not mist cacti (Joy Us Garden). A pot that is still heavy, or soil that is damp an inch down, means wait.

• Soil. UMN Extension's mix is one part potting soil to one part coarse sand. Its test: moisten the mix and squeeze it; it should fall apart when you open your hand. Joy Us Garden avoids ordinary potting soil on its own.
• Pot. At least one drainage hole (Joy Us Garden). Planet Desert recommends a new pot only 2 to 3 inches wider than the old one, because an oversized pot holds too much water.
• Repotting. Rarely. Joy Us Garden repots small cacti about every five years, in spring, summer or early autumn, one pot size up.
• Handling. Joy Us Garden wraps the plant in bubble wrap and uses kitchen tongs to avoid the spines.
• Propagation. Let cut pieces callus for 7 to 10 days before planting them in dry mix (Joy Us Garden); pups can be separated the same way (Planet Desert).

Very little. UMN Extension uses a houseplant food higher in phosphorus than nitrogen, diluted to half the recommended rate, once or twice a year in late spring or summer. Planet Desert feeds once a year in spring with a balanced fertilizer such as 5-10-5 at half or quarter strength. Joy Us Garden feeds two or three times a year at half strength. None of them feeds in autumn or winter, and Planet Desert lists overfeeding as a mistake.

Cacti flower after a cool, dry, bright winter. UMN Extension's recipe for indoor flowers is good light, dry soil and cool nights, which a windowsill usually provides. Planet Desert gives 50 to 55 F nights as the cool period that matters for blooming, and 60 to 75 F as the normal indoor range. Joy Us Garden notes that flowering indoors is possible but uncommon, and that the flowers often last only one to three days.

The usual reason a healthy cactus never flowers is a warm, well-watered winter in a heated room.

Overwatering. Planet Desert names it the leading cause of root rot, Joy Us Garden says cacti are prone to rot if overwatered, and UMN Extension says excess water causes decay quickly. The other mistakes the sources list:

• Too little light. Leads to weak, stretched growth (Planet Desert, Joy Us Garden).
• A pot without drainage, or one that is too big (Planet Desert).
• Overfeeding (Planet Desert).
• Mineral build-up from tap water (Planet Desert).
• Sudden full sun outdoors. Joy Us Garden starts plants in shade and moves them into sun gradually, because direct afternoon sun burns an indoor cactus.
• Misting. Cacti prefer dry air (Joy Us Garden, Planet Desert).

Not in any way the sources support. University of Minnesota Extension says coffee grounds feed soil organisms and make an excellent addition to compost, but have not been shown to consistently lower soil pH, which is the usual reason people add them. None of the cactus guides we read (UMN, Planet Desert, Joy Us Garden) uses them.

For a cactus the practical problem is moisture: a layer of damp grounds on top of the pot keeps the surface wet, and wet soil is what kills cacti. Put the grounds in the compost and use the half-strength feed described above.

• Tall, thin, pale growth toward the window. Too little light (Planet Desert, Joy Us Garden).
• Soft, dark, collapsing base. Rot from wet soil (UMN). Cut off rotten tissue, let the healthy part callus, and replant in dry mix.
• White cottony tufts in the crevices. Mealybugs. UMN wipes them off with a cotton swab dipped in alcohol; Joy Us Garden checks the base and crevices monthly.
• Hard, brown bumps that scrape off. Scale; treat the same way (UMN).
• Bleached or brown patches on the sunny side after a move outdoors. Sunburn (Joy Us Garden). The scar is permanent; acclimate gradually next time.
• Shrivelling in winter. Some shrinking is normal when it is kept dry; UMN waters sparingly to stop it going too far.

For new plants, Planet Desert keeps them apart from the collection for two to three weeks so any pests show up first. Our pest guide has photos of each insect.

Several plants sold as cacti need different care or handling:

• Christmas, Thanksgiving and Easter cacti are forest cacti. Planet Desert notes that forest cacti need more frequent watering than desert types. Use our Christmas cactus guide, not this page.
• Pencil cactus (Euphorbia tirucalli) is not a cactus at all. NC State Extension places it in the spurge family and warns that its milky sap is very caustic: it can cause mild to severe skin irritation, and in the eyes it can cause temporary to permanent damage to the cornea. Wear gloves and eye protection when cutting it. Some cactus guides, including Planet Desert's, list it among cactus types.
• Aloe, jade and other succulents share the dry-soil rule but have their own needs; see aloe vera care and jade plant care.

A photo of the whole plant in PlantLens tells you which one you have before you choose a routine.

Joy Us Garden cites the ASPCA as listing cacti non-toxic, but notes that the spines are a hazard for curious pets. The bigger risk in a house with pets or children is the look-alike: pencil cactus sap is caustic to skin and eyes (NC State).

If a pet has chewed a plant and you are not sure what it was, call your vet or the ASPCA Animal Poison Control Center on (888) 426-4435. For a person with sap in the eyes or mouth, call Poison Control on 1-800-222-1222.

Research and drafting for this page were done with the help of AI, and every figure was then checked line by line against the sources listed at the end of the page. Sources were opened on 2026-09-25. If you find a mistake, tell us and we will correct it.