Etiolation is the thin, pale, stretched growth a cactus makes when it grows without enough light. More light fixes the growth that comes next. The part that has already stretched generally stays narrow.
The short version
- Etiolated growth is narrower and paler than the stem below it, often with a pointed tip. It means the plant has been growing in too little light.
- It often happens over a winter indoors, when the room is warm enough for the plant to keep growing and the light is too weak for it to grow well.
- More light fixes new growth only. Growth made in good light comes in at normal width, and the stretched part generally stays narrow.
- Raise the light gradually, over several weeks, because a cactus kept in low light can sunburn.
- To help prevent it next winter, rest the plant somewhere cool (about 45 to 55 F), bright and nearly dry, or add a grow light.
- A narrow section left from an earlier dark spell does not mean the plant is sick now. Leave it, or cut it off in warm weather once the plant is in better light.
What it looks like
Look at the top of the stem, where new growth forms, and compare it with the older stem below.
- Narrower. The newest growth is thinner than the stem below it.
- Paler. It is a lighter green than the older stem.
- Pointed. The tip often tapers toward a point, where a healthy tip is broad and rounded.
- Leaning. The stem bends toward the window or the brightest side.
It is easiest to see on a columnar cactus, one of the tall, upright kinds such as San Pedro, because a healthy column generally holds about the same width as it climbs. On a round cactus, the top grows up into a narrow, misshapen neck.
If the stem narrows and then widens again, with full-width growth above a narrow waist, the plant stretched during an earlier dark spell and has had enough light since. The light needs no change.
A stem that has shrunk along its whole length, with wrinkled skin, points to water, not light. See overwatering and underwatering.
Why it happens
A plant that is short of light stretches toward what light there is, and the growth comes in thin. A cactus stretches wherever it is warm and watered enough to keep growing but the light is weak:
- in a room, set back from the window
- at a window that gets no direct sun
- in deep shade outdoors
In winter the days are short and the light through a window is weak. A heated house may stay warm enough for a cactus to go on growing, and growth made in those months is often stretched.
Preventing it in winter
A cactus kept cool and nearly dry rests through the winter and makes little or no new growth, so there is little to stretch.
- Cool. Keep it at about 45 to 55 F.
- Bright. Use the brightest cool spot you have.
- Nearly dry. Water just enough to keep the stem from shriveling. That usually means a light watering every few weeks.
If you have no cool spot, the plant will keep growing, so it needs more light. Put it at your sunniest window (in the Northern Hemisphere, one facing south or west) and add a grow light, a lamp that adds to the light from the window. Fluorescent tubes go 6 to 12 inches above the plant and run 14 to 16 hours a day. Growing cactus indoors covers windows and lamps.
What happens to the stretched section
The stem generally keeps the width it had when it grew. On many cacti, round barrel types in particular, the narrow growth stays with the plant for good.
Once the plant has enough light, new growth at the tip comes in at normal width and color. A column ends up with a narrow waist between 2 full-width sections.
Giving it more light
1. Pick the brighter place.
- Your sunniest window. One that gets direct sun for several hours a day.
- Outdoors for the warm months. Move the plant out once the weather has warmed.
- A grow light, set at the distance and hours given above under "Preventing it in winter", where neither of those is possible.
2. Build up to it over several weeks. A cactus that has lived in low light can sunburn if it goes straight into direct sun, and that includes full sun through bare window glass.
- At a window: for the first few weeks, hang a sheer curtain or set the pot back from the glass. Then take the curtain away or move the pot closer, a little at a time, until it stands close to the glass.
- Outdoors: for the first few weeks, keep it in partial shade, in a spot that gets no direct sun between about 11 a.m. and 3 p.m. Then move it to sunnier spots a little at a time.
If the skin on the sunny side turns yellow, that is the first sign of sunburn. Move the plant back to a shadier spot and go more slowly. Skin that has turned straw-colored and dry is a permanent scar. Cactus sun and light explains acclimation, and corking, sunburn and rot covers the marks.
3. Watch the tip. The light is enough when new growth is as wide as the healthy stem lower down, a normal green, with a rounded tip. A resting cactus makes little or no growth in winter, so judge it in the warm months. If new growth still comes in thin, the plant needs more light than it is getting.
Leaving the narrow section
The section can stay if the plant stands firmly. Some growers tie a stem that leans or wobbles at the narrow point loosely to a stake pushed into the pot.
Cutting it
Cutting is optional, and it suits a columnar cactus. Cut if the stem is unsteady above the narrow section, or if you want an even column. Do it when both of these are true:
- The plant is already standing in its brighter place and has been built up to it without burning. In dim light the regrowth may stretch as well.
- The weather is warm, with nights at about 60 F or above.
Use a sharp knife. Wipe off any sap and dirt, then wipe the blade with 70% isopropyl alcohol so it stays wet for at least 30 seconds. Let it air dry.
If the thin growth is the top of the plant, make 1 cut. Cut at a slant across the full-width stem, just below the point where it starts to narrow, so the plant left in the pot is full width right up to the cut. That plant often sends out 1 or more new stems near the cut, and in good light they generally grow at normal width. The thin top generally stays thin if rooted.
If there is full-width growth above a narrow waist, make 2 cuts, once the top has a few inches of full-width stem.
- Cut at a slant just above the waist, at the point where the stem is back to full width. Root the full-width piece you lift off.
- Cut at a slant across the full-width stem just below the waist. The narrow piece between the 2 cuts is thrown away.
Leave the cut on the plant in the pot dry and open to the air while it heals. Taking cactus cuttings covers the cut itself.
A cutting, meaning a piece of stem with no roots, has to dry before it is planted. Stand it somewhere dry and airy until the whole cut face is dry and firm to the touch. That seal is called a callus. Then plant it cut end down. Give an unrooted cutting no water until it has rooted. Rooting takes 4 to 8 weeks. See how to root a cactus cutting.
Sources
Common Problems and Issues of Succulents. Aaron Steil, Iowa State University Extension and Outreach, reviewed 2023. https://yardandgarden.extension.iastate.edu/how-to/common-problems-and-issues-succulents
Indoor Cacti. Karen Russ, Al Pertuit and Barbara H. Smith, Factsheet HGIC 1502, Clemson University Cooperative Extension Home and Garden Information Center, revised 2015. https://hgic.clemson.edu/factsheet/indoor-cacti/
Cacti and succulents. Deborah L. Brown, University of Minnesota Extension, reviewed 2026. https://extension.umn.edu/houseplants/cacti-and-succulents
Lighting for Indoor Plants. University of Maryland Extension, 2023. https://extension.umd.edu/resource/lighting-indoor-plants
How to grow houseplant cacti and succulents. Royal Horticultural Society. https://www.rhs.org.uk/plants/types/cacti-succulents/houseplants/growing-guide
Care for Potted Cacti and Other Succulents in Desert Climates. Arizona-Sonora Desert Museum. https://www.desertmuseum.org/visit/sheets/1Cact_pot.pdf
Problems and Pests of Agave, Aloe, Cactus and Yucca. Jack Kelly and Mary W. Olsen, University of Arizona Cooperative Extension, revised 2011. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1399.pdf
How to Propagate Agaves and Cacti from Cuttings and Seed. Jack Kelly, University of Arizona Cooperative Extension, 2009. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1483.pdf