Cacti are some of the easiest houseplants to keep alive, and also some of the easiest to drown. Clemson Extension puts it simply: most cacti tolerate neglect but thrive with good care, and watering properly is the most important factor in growing them successfully. This guide covers cactus care indoors for the common desert cacti: light, soil, the soak-and-dry watering rhythm, winter rest, repotting, propagation, root rot, pests and pet safety.
Cactus Care at a Glance
| Factor | What desert cacti need |
|---|---|
| Light | Bright sun: a south or west window with several hours of direct sun; grow lights if needed |
| Soil | Free-draining: commercial cactus mix, or equal parts potting soil and coarse sand or grit |
| Water (spring to early fall) | Water thoroughly, then let the soil dry out completely |
| Water (winter) | Only enough to keep the plant from shriveling, usually a light watering every few weeks |
| Temperature | 65 to 85 °F in growth; 45 to 55 °F in winter rest is ideal |
| Feeding | Low-nitrogen fertilizer (Clemson: 5-10-5 monthly June to September; UMN: once or twice in late spring or summer at half strength) |
| Repotting | Only as needed, into a slightly larger pot, in spring |
| Pets | Most true cacti non-toxic to cats (ASPCA); spines can injure |
Sources: Clemson HGIC 1502 Indoor Cacti; University of Minnesota Extension; ASPCA.
This guide is about desert (arid climate) cacti, the spiny kinds most people picture. Jungle cacti such as Christmas cactus need different care; see our Christmas cactus guide.
Light
Clemson says arid climate cacti need bright sunlight and that south- or west-facing windows with several hours of direct sun each day are ideal, with artificial light used to supplement if necessary. University of Minnesota Extension agrees that cacti need abundant light and suggests, where window light falls short, fluorescent tubes 6 to 12 inches above the plants for 14 to 16 hours a day (modern LED grow lights work too; see our grow light guide).
Too little light causes etiolation: the cactus stretches toward the window, grows thin and pale, and the new growth is narrower than the old. That stretched growth won’t thicken again, but new growth will be normal once light improves. When moving a cactus into stronger light, or outdoors for summer, do it gradually: Clemson advises partial shade for the first few weeks outdoors, and UMN warns against hot sun from 11 a.m. to 3 p.m. at first, to avoid sunburn.
Soil
Clemson notes that cacti actually like a rich soil as long as it drains freely, and recommends commercial cactus mix or a homemade mix of equal volumes of peat-based potting soil and very coarse sand or grit. UMN suggests one part potting soil to one part coarse sand and offers a simple test: moisten the mix and squeeze it; when you open your hand, it should fall apart. Pumice or perlite can replace some of the sand; see our vermiculite vs perlite guide.
Pots and Repotting
Always use a pot with drainage holes. UMN warns that excess water trapped in the soil causes rotting in a very short time. Terracotta dries faster than plastic or glazed ceramic, which suits cacti, but any pot works if it drains and you water carefully.
Clemson says cacti like to be slightly pot-bound and should be repotted only as needed, ideally in April as they start summer growth, into a container only slightly larger than the current one, because an oversized pot stays wet and can lead to rot. Its repotting tips:
- Wear heavy leather gloves, or wrap the cactus in several layers of newspaper to handle it.
- Ease it out, shake off old soil and check the roots.
- Set it at the same depth in fresh, dry cactus mix.
- Wait several days before watering, and don’t fertilize newly repotted plants.
How to Water a Cactus
The soak-and-dry rhythm is the core of cactus care:
- Spring to early fall: Clemson says cacti grow quickly from March to September and should be watered like other houseplants that prefer to dry slightly between waterings. UMN adds: always allow the soil to dry out completely between waterings.
- Water thoroughly until water runs from the drainage holes, then discard the excess after a few minutes (UMN). UMN warns that repeated shallow sprinklings often result in distorted growth.
- Winter: water just enough to keep the plant from shriveling, usually a light watering every few weeks (Clemson).
- Never let the pot stand in water. Clemson notes waterlogged soil quickly leads to root rot.
Check the soil rather than the calendar: push a finger or a wooden skewer into the mix; water only when it comes out dry. Pots dry more slowly in cool, dim weather, so the interval stretches a lot in winter. For bottom watering, see our bottom watering guide.
Winter Rest and Flowering
Clemson says dormant cacti do best at 45 to 55 °F in winter, for example in a cool, sunny room or near a cooler window. Most tolerate normal house temperatures, but they are more likely to flower and prosper if kept cool in winter. UMN explains that you may be able to bring cacti into bloom indoors by recreating their native winter conditions: good light, dry soil and cool nights. It names Mammillaria, Gymnocalycium, Lobivia and Rebutia as among the easier cacti to flower indoors.
Skip fertilizer in winter. Clemson recommends a low-nitrogen fertilizer such as 5-10-5 once a month from June through September, or a time-release fertilizer once in spring; UMN suggests feeding cacti only once or twice in late spring or summer, with a houseplant food higher in phosphorus than nitrogen at half strength.
Cactus Roots
Most desert cacti have fairly shallow, spreading roots adapted to catch water quickly after rain, which is one reason they do best in a pot that is not much bigger than the root system and a mix that dries out between waterings. Healthy roots are firm and light-colored; dark, mushy roots mean rot. Because cacti store water in their stems, they can survive weeks without water, but they cannot survive roots sitting in wet soil.
Propagating Cacti
Clemson lists seeds, cuttings, grafting and offsets, and UMN calls stem cuttings an easy method. For a home grower:
- Offsets (pups): wearing thick gloves, cut or twist off a pup at its base.
- Stem cuttings: cut a segment or branch with a clean knife.
- Let it callus: leave the cut end to dry in a shaded spot until a dry skin forms over the wound before planting, as Iowa State Extension advises for succulent cuttings. Planting a fresh, wet cut invites rot.
- Plant the callused cutting in dry or barely moist cactus mix, upright, and wait until roots form before watering normally.
Root and Stem Rot
Clemson says that in the home, diseases are rarely a problem except for root and stem rots, which usually result from a soil mix that doesn’t drain quickly or from watering too often. Signs include a soft, discolored, mushy base or stem and a plant that wobbles in the pot.
- Unpot the cactus and remove the old soil.
- Cut away all soft, dark tissue with a clean knife until only firm, healthy tissue remains. If the base is rotten but the top is firm, cut off the healthy top and treat it as a cutting.
- Let the cut surfaces callus over in a dry, shaded place.
- Replant in fresh, dry cactus mix in a clean pot with drainage, and wait before watering.
For more on rot, see our root rot guide.
Pests
Clemson lists aphids, spider mites and mealybugs as the major pests of cacti, with scale also possible and harder to control. It advises checking new plants before purchase and using houseplant insecticidal sprays or soaps labeled for cacti, following the label. A light scale infestation can be picked off by hand; a heavy one may mean discarding the plant. See our guides to mealybugs, spider mites and scale.
Are Cacti Toxic to Pets?
Mostly non-toxic, but spines hurt
The ASPCA’s cat list includes several true cacti as non-toxic: Christmas cactus, Easter lily cactus (Echinopsis multiplex), old man cactus, thimble cactus (Mammillaria fragilis) and tree cactus (Opuntia species). But “pencil cactus” (Euphorbia tirucalli) is not a true cactus and is listed as toxic. Even non-toxic cacti can injure a pet’s mouth or paws with their spines, so keep spiny plants out of reach.
See our cat-safe plants list for more options.
Troubleshooting
| What you see | Likely cause | Fix |
|---|---|---|
| Soft, mushy, dark base or stem | Root or stem rot from wet soil | Cut away rot; callus; repot in dry mix |
| Thin, pale, stretched growth leaning to the window | Too little light (etiolation) | Move to a sunnier window or add a grow light |
| Wrinkled or shriveled, soil bone dry | Underwatering | Water thoroughly; resume regular soak-and-dry |
| Shriveled with wet soil | Roots have rotted and can’t take up water | Check roots; treat as rot |
| Yellow, bleached or brown patches on the sunny side | Sunburn after a sudden move into strong sun | Shade and reintroduce sun gradually |
| Distorted growth | Repeated shallow watering (UMN) | Water thoroughly, less often |
| Cottony tufts, webbing or bumps | Mealybugs, spider mites or scale | Isolate and treat |
| No flowers | Warm, wet winters | Give a cool, dry, bright winter rest |
Sources: Clemson HGIC 1502; University of Minnesota Extension. Fixes are general practice.
Frequently Asked Questions
How often should you water a cactus?
From spring to early fall, water thoroughly whenever the soil has dried out completely. In winter, Clemson recommends watering just enough to prevent shriveling, usually a light watering every few weeks.
How much light does a cactus need indoors?
A lot. Clemson recommends a south- or west-facing window with several hours of direct sun daily; UMN suggests grow lights 6 to 12 inches above the plants for 14 to 16 hours if window light is not enough.
What soil is best for cactus?
A free-draining mix: commercial cactus mix or equal parts potting soil and coarse sand or grit, as Clemson and UMN recommend. The moist mix should fall apart when squeezed.
How do I know if my cactus has root rot?
The base or stem turns soft, dark and mushy, and the plant may wobble or shrivel even though the soil is wet. Unpot it, cut away all rotten tissue, let it callus, and replant in dry mix.
How do you get a cactus to flower?
Give it a cool, dry, bright winter rest. Clemson suggests 45 to 55 °F in winter, and UMN says good light, dry soil and cool nights recreate the conditions that bring cacti into bloom.
Are cacti toxic to cats?
Most true cacti are listed as non-toxic to cats by the ASPCA, but spines can injure pets. “Pencil cactus” is a toxic Euphorbia, not a true cactus.