What you see
Firm raised blisters or corky tan bumps on leaf undersides, mostly on older leaves, with no insects and no spreading edge.
It is not a disease and it does not travel to the next plant. What it points to is a combination of a wet pot and conditions where the plant is barely drinking.
What it looks like, and what it is not
Look at the underside of an affected leaf in good light. Early edema looks like tiny water filled blisters in even numbers across the surface. Older damage is tan or brown, raised and corky, and the leaf may curl or cup around it.
It appears on the oldest and largest leaves first, because they were on the plant while the conditions built up. New leaves that open afterward come out clean if the conditions changed.
Rub a spot with a finger. Edema is part of the leaf and does not move. Scale insects lift off with a fingernail, mealybugs smear white, and sooty mold wipes away.
There is no webbing, no honeydew, no insects and no spreading margin. A spot that grows week by week or has a yellow halo around it belongs to another page.
Look at
- 01Whether the bumps are on the underside of older leaves
- 02Whether they are firm and part of the leaf when rubbed
- 03Whether any insects sit on the undersides or axils
- 04How wet the pot and the outer pot have been kept
- 05How much light and air movement the spot gets
What to do now
Confirm it is part of the leaf by rubbing a spot, then look at the pot and the room rather than reaching for a spray.
Most likely cause
Watering while the plant is barely drinking
This is the usual combination. A cool, dull room in winter, a plant with slowed growth, and a watering rhythm carried over from summer. The roots keep taking water up and the leaves are giving off very little, so the pressure has nowhere to go.
A pot that stays wet and an outer pot holding water out of sight both keep the roots supplied around the clock, which makes it more likely.
Water less often and let the mix dry down further between waterings than you would in summer. Feel it an inch or two down and water only if it is dry there.
Empty the saucer and the outer pot after every watering. That single habit removes the constant supply that keeps the pressure up.
Water in the morning where you can, so uptake happens while the plant is lit and giving off water rather than through the night.
What you see
The room is cool or dull, growth has slowed, and the pot is watered on the same rhythm as in summer.
What to do now
Let the mix dry further between waterings, empty the saucer and outer pot every time, and water in the morning rather than at night.
Damp still air around the leaves
Leaves give off water into the air around them. When that air is already damp and does not move, the leaf cannot lose much, and the water arriving from the roots stays.
Crowded shelves, a group planting, a closed bathroom, a propagation box and a plastic cover over a new cutting all produce that. A humidifier running close to a plant in a cool room does the same.
Move the plants apart so air passes between them, and open the room up for a while each day.
This is where the standard advice to raise humidity works against you. A plant showing edema is not short of water in the air, so a pebble tray or a humidifier makes the picture worse rather than better.
What you see
The plant stands in crowded, still, damp air, under a cover or in a closed room, and the leaves stay wet looking.
What to do now
Space the plants out, get air moving in the room, take covers off, and stop adding humidity while the bumps are appearing.
Low light with plenty of water
Light drives the whole process. A plant in a dim corner gives off far less water than the same plant on a bright sill, whatever the pot is doing.
A dark spot combined with a regular watering routine produces the same pressure as an overwatered pot in good light. Short winter days do it to plants that were fine all summer.
Move the plant closer to the window for the dim months, or add light. Then adjust the watering to what the plant is actually using in that spot.
Some plants show this readily and others almost never. Thick leaved plants such as peperomia, jade plant and succulents, ivy, and a number of begonias are the ones that turn up with it most.
What you see
The plant sits well back from a window or in a dim room, and it is watered on a fixed routine through the dark months.
What to do now
Move it nearer the light or add a grow light, then water on what the mix tells you rather than on a set day.
What to do about the marked leaves
The bumps are healed tissue and they stay. No treatment turns them back, and there is nothing to spray for.
Leave the leaves on the plant. They still work, and a plant that has just been through this needs the leaf area it has.
Take off only leaves that are more damaged than sound, or badly cupped, and only once the plant is growing again.
Read the result on the leaves that open next. Clean new growth means the conditions changed, and it is the only confirmation you get.
Why this stays a working explanation
Corky bumps on a leaf underside also come from old thrips scarring, from mite damage on some plants, and from chemical residue after a spray. Those are told apart by looking for the insects and by knowing what has been applied.
Check the undersides and the leaf axils in good light before settling on edema. It is faster to rule out an insect than to explain a spray that did not work.
Change one thing at a time and note the date. Watering, position and airflow changed all at once leave you with an improvement and no idea which change earned it.
Related plants
Keep reading
Common questions
What is edema on plant leaves?
Small raised blisters or corky brown bumps that form when roots take up more water than the leaves give off. Cells swell and burst, and the tissue that heals over stays raised. It is a response to conditions rather than a disease.
Is edema on plants contagious?
No. It is a physical response inside the plant, so it does not move to a neighbor. Several plants on the same shelf can show it at once because they share the room, the light and the watering routine.
How do you treat edema on leaves?
By changing the conditions rather than by spraying. Let the mix dry further between waterings, empty the saucer, move the plant into better light, and get air moving around the leaves. The existing bumps stay.
Do edema bumps go away?
No. That tissue has healed over and keeps its shape. The measure of success is that the leaves opening after the change come out clean.
How do I tell edema from scale insects?
Rub the bump. Scale lifts off with a fingernail and leaves a mark on the leaf, and edema is part of the leaf and does not move. Scale also comes with a sticky film on the leaves below, which edema never does.
Which plants get edema most often?
Thick leaved plants show it most, including peperomia, jade plant and other succulents, along with ivy and a number of begonias. Any plant can show it under a wet pot with dim light and still, damp air.
Last reviewed: 2026-09-07