Black or Brown Spots on Houseplant Leaves

Causes and how to tell them apart

1. Fungal leaf spot[1][2]

   How to tell: Small brown spots with yellow edges, sometimes in rings like a target. Tiny black dots may show in dead tissue, and spots can merge.

2. Bacterial leaf spot[1][3]

   How to tell: Spots look watery or water-soaked, often with a yellow halo, and are about the same size. They can be angular between veins, may ooze, and dead tissue can be soft and smell rotten.

3. Anthracnose[1]

   How to tell: Damage starts at the leaf tips, which turn yellow, then tan, then dark brown, and the browning can wrap around the leaf.

4. Too much sun (sunburn)[4][5]

   How to tell: Spots often follow a recent move to a brighter spot. If spots keep appearing, the light is the likely cause.

5. Cold water, chilling or aerosol damage[6][4]

   How to tell: White or straw-colored spots or rings point to cold water splashes or aerosol damage. Chilling below 50 degrees F and spray injury can also cause spots.

6. Overwatering (oedema)[6][1]

   How to tell: Look for raised, corky patches on the undersides of leaves. This points to too much water, especially with poor airflow and humid air, rather than disease.

7. Salt buildup, dryness or low humidity (brown tips and edges)[1]

   How to tell: Brown that sits on the tips or edges of leaves, rather than in round spots, fits dry air, watering problems or salt buildup. A white or grey crust on soil or pot rim means salts.

What to do, step by step

1. Pick off spotted leaves and throw them away.[2][1]
2. Water early in the day so leaves dry fast, and avoid splashing water on the leaves.[2][1]
3. Give plants room so air can move between them, and lower humidity around them.[2]
4. If spots keep showing on leaves facing a bright window, move the plant to a spot with less sun.[5]
5. If overwatering is a possibility, tip the plant out and check the roots. If roots are brown, rotted and soft, you probably need to water less.[6]
6. Skip fungicide at first. Cleaning up the plant and drying the conditions often works in home settings. A plant with a body-wide bacterial infection should be thrown out.[2][3]

How to prevent it

• Give plants good air circulation and do not crowd them.[1]
• Do not mist the leaves of plants prone to leaf disease.[1]
• Inspect new plants before buying and reject any with leaf spots, since those blemishes will not go away.[4]
• Scrub used pots clean before reusing them and use fresh potting mix when repotting.[1]