PlantRx

Aloe vera black spots

By Karim DiabatePublished Updated How these guides are built

Black, as opposed to brown, usually means wet. On an aloe vera it points at rot or at an infection far more often than at dryness or sun, and the first thing worth checking is the roots rather than the leaves.

A healthy Aloe Vera, photographed for reference
A healthy aloe vera for comparison. This is a reference photo, not a picture of the problem. Photo by MidgleyDJ and Wikimedia Commons contributors (CC BY-SA 3.0), via Wikimedia Commons.

What is specific to this plant

  • A thirsty aloe curls its leaves inward and they feel thin and flat. A drowning one goes soft and translucent from the base up. These look nothing alike once you know to check the texture.
  • Aloe grown in too little light flops outward from the centre instead of holding an upright rosette, and it will not stand back up.
  • Reddish or bronze leaves are usually sun stress or cold, and are not a disease.

What it could be, and how to tell

These look alike in a photograph, so each one below lists what you would ALSO see if that is the cause. Work down the list and stop at the one where the other symptoms match too.

most common

1. Rot working up from the roots

What else you would see

  • black or very dark spots that feel soft or damp rather than crisp
  • the lowest leaves affected first
  • a sour smell, and mix that stays wet
How to confirm it: Slide the plant out of its pot and look at the roots. Healthy ones are firm and pale. Brown, soft, or hollow when you press them means rot, and that changes what you do next completely.

What to do

  1. Stop watering and let it dry down this far: the whole pot.
  2. Check that the pot drains and empty any saucer or decorative outer pot it sits in. Water held out of sight keeps the mix wet whatever you change above it, and it stays invisible until you lift the pot.
  3. If the roots are soft and brown, trim them back to firm tissue with a blade sterilised first and repot into fresh gritty cactus or succulent mix.
common

2. Bacterial leaf spot

What else you would see

  • dark spots with a yellow halo, often with a wet or greasy look
  • new leaves affected as well as old
  • rapid spread, noticeable day to day
How to confirm it: A greasy, water-soaked look with a yellow edge, spreading fast and ignoring the usual bottom-to-top order, points at bacteria rather than at watering.

What to do

  1. Isolate the plant straight away.
  2. Cut away affected leaves with a sterilised blade and bin them.
  3. Stop misting, keep the foliage dry, and improve airflow.
  4. If you use any treatment product, follow its label exactly.
common

3. A bruise where the leaf's own sap has leaked inside it

What else you would see

  • a dark patch in the shape of a knock, a fingermark or the pot rim it was pressed against
  • the mark staying exactly the size it started at over several weeks
  • the leaf still firm all around it, with no softness spreading outward
  • a yellow-brown weep at any cut or torn edge on the same leaf
How to confirm it: Ask whether the mark could have been a knock, and then watch its edge rather than treating it. An aloe leaf carries a bitter yellow sap in a layer just under the skin, and when the leaf is crushed or bent that sap leaks into the tissue and dries dark, which is why a bruise on this plant goes black rather than merely dented. A mark that does not grow and sits in firm tissue is that. A mark spreading outward, with softness around it, is rot and the causes above apply.

What to do

  1. Nothing to treat. The mark is dead tissue in a living leaf and it stays as it is.
  2. Move the plant so its leaves are not pressed against a window, a wall or the pot rim, which is where most of these come from.
  3. Take the leaf off at the base for appearance if you want to, cutting close and cleanly, and expect it to weep as you do.
less common

4. Cold damage

What else you would see

  • damage that appeared within a few days of a cold snap, or of the heating or air conditioning coming on
  • the plant sits near a window, an exterior door or a vent
  • the damage is worst on the side facing the cold
How to confirm it: Sudden onset on the exposed side only, following a temperature change. A leaf resting against cold glass overnight is enough to do it.

What to do

  1. Move the plant away from the glass, the door or the vent.
  2. Damaged tissue will not recover. Leave it unless it turns soft, which is the point at which it can start to rot.
less common

5. Physical damage

What else you would see

  • isolated marks that have not changed in size for weeks
  • marks where the leaf touches a wall, a pot or another leaf
  • no new leaves affected
How to confirm it: A mark that does not spread over two or three weeks, and that no new leaf repeats, is damage rather than disease.

What to do

  1. Nothing to treat.
  2. Give the plant enough room that its leaves are not rubbing against anything.

Common questions

Black spots or brown spots, does the difference matter?

Yes. Black and soft usually means water and rot. Brown and crisp usually means dryness, sun or age. They are close to opposite problems and the responses do not overlap.

Is it contagious to my other plants?

A bacterial or fungal leaf spot can spread, particularly on wet foliage in still air. Rot caused by overwatering does not spread from plant to plant, though the habit that caused it usually affects several.

Can I just cut the black parts off?

Removing affected leaves helps and is worth doing, but it treats the symptom. If the roots are rotting, nothing improves until the roots and the mix are dealt with.

Before you act on any of this

This is general plant care guidance for a plant, not advice about people or animals. We never tell you whether a plant is safe to eat or touch, and we never tell you a plant is safe for a child or a pet. If a child or animal may have eaten any part of a plant, contact Poison Control (US 1-800-222-1222) or a vet immediately rather than reading further.

Treatment advice here is deliberately category level. We do not give product names, mixing ratios or application intervals. Whatever the label on the product in your hand says is the instruction that counts, and following it is your responsibility.

Where this comes from

The general horticultural facts behind this differential come from published university extension and Royal Horticultural Society guidance. What is specific to this plant, and the order the causes are ranked in, is ours, and the methodology page says where that reasoning stops being reliable.

Other aloe vera problems

Not sure which one it is?

PlantRx is an iPhone app that reads the photo and gives you the same kind of ranked differential you just read, for your plant specifically, with the evidence it based each answer on. The first diagnosis is free, in full. There is no subscription and no account.

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