A cactus that changes shape is worrying, because cacti usually change so slowly. The two most common changes look similar at a glance and need opposite fixes. A wrinkled cactus is often short of water. A soft one is often rotting, and more water makes it worse.

Before you water, press the plant gently with a gloved finger and check the mix. Those two checks sort out most cases. This guide also covers the look-alikes: cold damage, sunburn, low-light stretching and the normal brown bark of older cacti.

The two-minute check

What you seeTextureMixMost likely
Shrivelled, wrinkled or deflated stemFirmDry well below the surfaceThirst
Wrinkled stemFirm or slightly soft at the baseWet for daysRoot loss from rot
Soft, dark, water-soaked patchMushyOften dampRot
Yellow then straw-coloured patch on the sunny sideDryAnySunburn
Black, then crisp, after frostSoft, then dryAnyFreeze damage
Thin, pale, stretched new growthFirmAnyToo little light
Tan, bark-like base on an older plantHard, dryAnyNormal corking

Virginia Cooperative Extension warns that wilting is the first symptom of both underwatering and overwatering. That is why the mix and the texture matter more than the shape.

Wrinkled and firm: thirst

Iowa State Extension describes underwatered succulents shrivelling, with stems and leaves that become wrinkled and mottled. Roots can die from lack of water. Clemson’s advice for dormant indoor cacti is to water just enough to keep them from shrivelling, so wrinkling in winter is a cue for a light drink.

Signs that point to thirst:

  • the stem is firm all over, including at the soil line;
  • the mix is dry several centimetres down, and the pot feels light;
  • the plant has gone a long time without water.

What to do:

  1. Water thoroughly until water runs from the drainage hole.
  2. Empty the saucer. Clemson says a cactus must never stand in water.
  3. Let the mix dry before watering again. Iowa State suggests checking that it is dry several inches down first.

If a firm, wrinkled cactus stays wrinkled after the mix has been thoroughly watered, check the roots. Iowa State notes that roots can die from lack of water, and dead roots cannot take it up.

Wrinkled on wet mix: roots lost to rot

A wrinkled cactus in mix that has been damp for days is a warning sign. Rotted roots cannot supply water, so the stem shrivels even though the pot is wet. Clemson says waterlogged soil quickly leads to rotting of the roots.

Unpot it and look. The UF Emerging Pathogens Institute says healthy roots are white and firm. Overwatered roots turn soft and brown, or even black, and the mix may smell sour.

Soft and mushy: rot

Soft tissue is the more serious problem. Iowa State lists yellowing and soft, mushy stems, with damp soil, as signs of overwatering. Clemson says root and stem rots usually come from a mix that does not drain quickly or from watering too often.

The Texas A&M Plant Disease Handbook describes bacterial soft rot of cacti and succulents as watery, soft, black tissue that deteriorates rapidly. It also describes a fungal stem rot that starts as yellow spots and can rot a plant at the base or top. Arizona Extension describes an internal soft rot of barrel cacti caused by Pythium, a soil organism favoured by moist conditions. Because that rot is internal, it is often too late to treat once you see it.

What to do:

  1. Stop watering and unpot the plant. Wear thick gloves or use tongs, as UF/IFAS suggests for spiny plants.
  2. Find the edge of the rot. Cut through the stem with a clean knife above the soft area, into firm, clean tissue.
  3. Decide what to keep. Iowa State says to discard the plant or propagate healthy-looking segments. If the rot runs through the whole stem, discard it.
  4. Callus before planting. Illinois Extension suggests letting a cactus or succulent cutting sit for 4–7 days before inserting it in a well-drained mix, to help prevent rot.
  5. Clean up. Do not reuse the old mix. Texas A&M advises treating broken surfaces promptly and keeping plants out of high humidity to limit soft rot.

The UF Emerging Pathogens Institute is blunt about bacterial infections in fleshy plants: throw the plant out and start over. Discarding is not failure if the rot is spreading fast.

Not rot: corking and scab

Older cacti often develop brown, bark-like tissue near the base. NMSU’s Southwest Yard and Garden notes that corky, often light brown or tan areas form naturally on older parts of a cactus. They can also follow scratches or insect feeding. Fungal lesions, by contrast, tend to be sunken and black.

Press it. Corking is hard and dry. Rot is soft and wet.

Texas A&M describes scab as rusty, corky areas on cactus stems, and recommends more light and lower humidity. Our prickly pear guide shows how scab looks on pads.

Cold and freeze damage

Clemson says cacti prefer 18–29 °C (65–85 °F) in the growing season and do best at 7–13 °C (45–55 °F) while dormant in winter. That cool rest is normal. Freezing is not.

Arizona Extension describes freeze damage on succulents as blackening of exposed parts, which dries and turns crisp after a few weeks. Barrel cacti may show straw-yellow rib edges, and columnar cacti may yellow and die back after a severe freeze. Damage from a short, mild freeze may only affect the skin, and the plant can outgrow it.

What to do: wait a few weeks for the damage to show fully before cutting. Arizona notes that container plants moved indoors until freezing weather passes, kept dry and in bright light, survive without damage.

Sunburn

Arizona Extension says plants not used to direct sun burn easily. They turn yellow, then the skin turns straw-yellow and dies, leaving a permanent scar. Iowa State notes that sun-damaged areas will not recover.

Burned tissue is dry, not mushy. Move the plant back, then raise light slowly. Clemson notes that forest cacti such as holiday cacti need bright but filtered light and may sunburn in direct sun.

Thin and stretched: too little light

Iowa State describes tall, spindly, pale new growth as a sign that light is too low. Clemson says desert cacti need bright sunlight, ideally direct sun for several hours a day.

Stretched growth is firm, so it is easy to tell from rot. Move the plant to brighter light gradually. Iowa State notes that some succulents recover over time, while others need the lanky growth cut back.

Holiday cacti are different

Christmas, Thanksgiving and Easter cacti are forest cacti. Clemson describes them as needing bright, filtered light rather than full sun. Their segments can go limp from either thirst or rot, so the same press-and-check approach applies. Our Easter cactus problems guide covers that group.

Prevent both problems

  • Water by the mix. Clemson suggests treating cacti like houseplants that dry slightly between waterings from March to September, then watering lightly every few weeks in winter. Iowa State suggests starting with every two to three weeks.
  • Use a fast-draining mix. Clemson suggests equal parts peat-based potting soil and very coarse sand or grit. Iowa State suggests one-third organic and two-thirds mineral material.
  • Keep the pot snug. Clemson warns that an oversized pot keeps the mix moist and can lead to rot. UF/IFAS says cacti like to be slightly pot-bound.
  • Choose terracotta. Iowa State and Virginia Extension note that clay pots dry faster.

For broader care, see our indoor succulent care guide and our houseplant root rot guide.

References