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How to Grow Cacti: Light, Grit and a Dry Winter Rest

Most cacti die from winter watering, not neglect. Gritty mix, the brightest window, a soak in summer and almost nothing from October to March.

By Zakaria 4 min read Save to Pinterest — opens Pinterest in a new tab
Cactus plants pots
Photo: milivigerova, Pixabay Content License, via Pixabay
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Nearly every dead cactus died of water in winter. Light, grit, and a genuinely dry rest from October to March is most of what there is to know.

The annual cycle

Most cactus advice is given as a set of rules. It makes far more sense as a year.

What the plant wants, month by month
PeriodWaterTemperatureFeed
March–AprilResume gradually, one light wateringRisingNone yet
May–AugustSoak when bone dry, every 2–3 weeksWarm, as bright as possibleLow-nitrogen cactus feed monthly
SeptemberReduceCoolingStop
October–MarchNone, or almost none8–12°C, brightNone

The winter rest is not neglect, it is the point

Desert cacti evolved around a dry season. Watering through winter in a warm room keeps them growing when they should be resting, produces weak etiolated growth, is the commonest cause of rot, and prevents flowering.

A cool bright windowsill in an unheated room, kept dry, is ideal. A warm living room with occasional watering is how most houseplant cacti slowly decline.

Soil and pots

Mix: cactus or succulent compost with a third to a half added perlite, pumice or coarse grit. The test is simple — water poured on should run straight through, not pool on the surface.

Pot: terracotta, which breathes and dries, with drainage holes. Only slightly larger than the rootball, because an oversized pot holds damp compost the plant is not using.

Top dressing: a layer of grit over the compost. It keeps the base of the plant dry — where rot starts — and stops compost splashing up the stem.

Watering, stated precisely

Soak thoroughly until water runs from the holes. Then do not water again until the compost is dry all the way through.

  • Summer: usually every two to three weeks
  • Winter: usually not at all
  • Test by weight. Lift the pot — a dry one is noticeably light
  • Never leave it standing in a saucer
  • Small frequent watering is the enemy. It keeps the surface damp and the roots permanently half-wet

Light, and the stretching problem

Cacti want the brightest position you have — a south-facing window in the northern hemisphere, or supplementary light.

In insufficient light the plant etiolates: it stretches toward the light, producing pale narrow growth that cannot support itself and looks nothing like the compact body below.

That growth does not thicken again. More light prevents further stretching but does not reverse what has happened. For a badly stretched plant the remedy is to behead it above firm growth, callus the cut, and re-root the top — see how to plant cactus cuttings.

Acclimatise before summer sun

A plant that has spent winter indoors will scorch if moved straight into full outdoor sun. Pale bleached patches are permanent.

Move it out over two weeks, starting in shade and increasing exposure gradually.

Getting them to flower

In order of importance:

  1. A cool dry winter rest. 8–12°C, bright, no water. The main trigger
  2. Maximum light in the growing season
  3. Maturity. Many species simply will not flower until they are several years old
  4. Low-nitrogen feed in summer — high nitrogen produces body growth at the expense of flowers
  5. Patience. Some species flower reliably every year; others do not

Desert cacti are not jungle cacti

Worth separating, because the advice above actively harms the second group:

  • Desert cacti — most of what is sold as “cactus”. Full sun, dry winter rest, gritty mix
  • Jungle cacti — Christmas and Easter cactus (Schlumbergera), Rhipsalis, epiphyllum. Bright indirect light, more water, more humidity, richer mix. They grow on trees in humid forest, and treating them like a desert plant kills them

If the plant has flat leaf-like segments and came from a garden centre at Christmas, it is the second kind.

Diagnosing problems

  • Soft brown base → rot. Cut above into firm tissue, callus, re-root
  • Soft and translucent overall → severe overwatering
  • Shrivelled, wrinkled, firm → underwatered. Soak it
  • Pale bleached patch → sunscald from moving it too fast
  • Thin stretched top → etiolation. Needs light, and probably beheading
  • White cottony fluff in the crevices → mealybugs. Alcohol on a cotton bud
  • No flowers, healthy plant → it is not getting a winter rest

Step by step

Time
P365D
Cost
20
You need
Cactus or succulent compost, Perlite, pumice or coarse grit, Horticultural grit for a top dressing
Tools
Terracotta pots with drainage holes, Thick gloves or folded newspaper

  1. Choose the brightest position you have

    A south-facing window or the equivalent. Insufficient light causes permanent stretching, and no amount of later correction thickens growth that has already etiolated.

  2. Mix a gritty compost

    Cactus or succulent compost with a third to a half perlite, pumice or coarse grit. Water poured on should run straight through rather than pooling.

  3. Pot into terracotta with drainage

    Only slightly larger than the rootball. Terracotta breathes and dries, and an oversized pot holds damp compost the roots are not using.

  4. Add a grit top dressing

    A layer of grit over the compost keeps the base of the plant dry, which is where rot starts, and stops compost splashing onto the stem.

  5. Water by soaking, then let it dry out fully

    Water until it runs from the drainage holes, then wait until the compost is dry all the way through — every two to three weeks in summer. Never water little and often.

  6. Feed lightly through summer only

    A low-nitrogen cactus feed monthly from May to August. High nitrogen produces soft body growth at the expense of flowers.

  7. Give a dry winter rest from October to March

    Move it somewhere bright at around 8 to 12°C and stop watering almost entirely. This rest is what prevents rot and what triggers flowering in most desert species.

  8. Acclimatise gradually before any summer sun

    A plant that has wintered indoors scorches in full outdoor sun. Move it out over about two weeks, starting in shade, since bleached patches are permanent.

Common questions

How often should you water a cactus?

Thoroughly, then not again until the compost is completely dry — which in summer usually means every two to three weeks, and in winter often means not at all. The common failure is small frequent watering, which keeps the surface damp while the roots sit in compost that never properly dries, and that is what causes rot. The rule that saves most plants is seasonal rather than numerical: water generously through the growing season, and give a desert cactus a genuinely dry rest from about October to March.

What soil do cacti need?

A gritty free-draining mix that water runs through rather than sits in — typically cactus compost with a third to a half added perlite, pumice or coarse grit. Standard houseplant compost holds far too much water and is the second most common cause of losses after overwatering. A top dressing of grit is worth adding as well, because it keeps the base of the plant dry where rot otherwise starts, and it stops compost splashing onto the stem.

Why is my cactus going soft and brown at the base?

Root or basal rot, almost always from overwatering, poor drainage, or watering during the winter rest. Once the base has gone soft the lower tissue is usually unrecoverable, and the practical response is to cut well above the damage with a sterile blade into firm green tissue, let the cut callus for a week or two, and re-root the top as a cutting in dry gritty mix. Discard the rotted base rather than attempting to save it.

Why won't my cactus flower?

Most commonly because it never gets a cool dry winter rest, which is what triggers flowering in a great many desert species. A cactus kept warm and watered year-round grows steadily and flowers rarely. Giving it a genuine rest — around 8 to 12°C, bright, and essentially no water from October to March — is the single most effective intervention. Age and light matter too: many species simply will not flower until mature, and a plant in insufficient light will not have the resources.

Why is my cactus growing thin and stretched at the top?

Etiolation, caused by insufficient light. The plant stretches toward the brightest source, producing pale narrow growth that cannot support itself and looks nothing like the compact body beneath. The stretched section will not thicken again — light prevents further stretching but does not reverse what has happened. If it is severe, the usual remedy is to behead the plant above firm growth, callus and re-root the top, and keep the result in considerably brighter conditions.

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