Plant diagnosis
Why does my geranium have brown spots?
Window-box pelargoniums are sun-and-air plants — yellow lower leaves mean wet soil, leggy growth means a dim corner, and blackened stem bases mean rot has won.
The 4 most likely causes
The cause of geranium brown spots usually narrows to one of the items below, ranked by how often we see each in Growli's diagnostic chats. Work down the list — most readers find their answer in the top two.
- Fungal or bacterial leaf spot (Possible)
Brown spots with yellow halos appearing on geranium, especially after water sat on the leaves overnight, are most often fungal or bacterial leaf spot. Remove affected leaves, water only at the soil line, improve airflow, and apply a copper fungicide if it spreads. - Sunburn or intense direct sun (Possible)
Bleached patches, papery brown spots, or crisped leaf surfaces on the south-facing side of geranium are sunburn. Acclimatise it more gradually after a move, or filter midday sun with a sheer curtain. Sunburn damage doesn't heal — wait for new growth. - Overwatering or poor drainage (Likely)
In most homes overwatering is more often a drainage problem than a frequency problem. Geranium needs a pot with a drainage hole, a chunky free-draining mix, and a watering rhythm of water deeply, then let the top third of the pot dry. Soggy soil drowns the roots and the first symptom you see above ground is yellowing or wilting foliage. - Pests sucking sap (Possible)
Sap-sucking pests (aphids, spider mites, mealybugs, scale) all cause similar symptoms: yellow stippling, distorted new growth, sticky residue. Inspect leaf undersides and stem joints with strong light. Most are controlled with weekly insecticidal soap or a horticultural oil spray.
Why geranium in particular
Brown spotting on a Pelargonium has a few distinct signatures. Corky, raised tan bumps confined to leaf undersides are edema, a watering-and-humidity fault rather than a disease. Fuzzy grey-brown rot spreading over leaves and stems in cool, damp air is botrytis. Most serious are small water-soaked spots that dry to brown, or brown V-shaped wedges biting in from the margins - the mark of bacterial blight, which turns leaves yellow and can go on to kill the whole plant systemically.
Normal turnover, or real trouble?
Cold nights and strong sun flush a geranium's older leaves red or bronze - a pigment response, not rot, fading as warmth returns. The horseshoe zone natural here is likewise no blemish. Treat brown marks as trouble only when active: water-soaked spots drying to dead patches, wedges eating in from the margins, or fuzzy grey growth in damp weather, all spreading leaf to leaf rather than colouring evenly.
How to diagnose in 60 seconds
Run these quick checks before you change anything — the right fix depends on what you find.
- Are the spots dry and crisp or wet and spreading? Crisp = sunburn, fluoride, or old damage; wet = active fungal or bacterial spot.
- Do the spots have a yellow halo? Halos are classic for bacterial and fungal leaf spot.
- Are they only on the sunny side of the plant? That points to sunburn.
- Are the leaf tips uniformly brown while the rest is healthy? Crispy tips on geranium usually mean low humidity or tap-water minerals.
The fix — step by step
Keep the leaves dry: water at the base, space plants so air moves between them, and clear fallen spotted leaves that harbour it. Pick off affected leaves with clean, dry hands. The one that changes everything is bacterial blight - the water-soaked spots and marginal wedges - because it lives inside the plant and travels in cuttings, so a blight-suspect geranium must be thrown out whole and never propagated from, however healthy its tips.
This is the recovery sequence Growli walks users through for geranium with brown spots. Work through the steps in order; skipping ahead is the most common reason a plant fails to bounce back.
- Quarantine if you suspect disease. If spots look wet, are spreading, or have a yellow halo, move geranium away from your other plants until you have a diagnosis. Disinfect your tools between plants.
- Remove the worst-affected leaves. Snip off heavily spotted leaves at the base. Don't compost them — bag and bin to stop spore spread. Never remove more than 30% of foliage in one go.
- Switch to filtered or rain water. If you suspect tap-water damage, water with rainwater, distilled water, or tap water that has stood uncovered for 24 hours. Continue for 4-6 weeks before re-evaluating.
- Improve airflow and watering technique. Water at the soil line only — never on the leaves. Space geranium so leaves are not touching neighbouring plants. A small fan in stagnant rooms makes a surprising difference.
- Apply a treatment if needed. For active fungal spread, a copper-based fungicide applied weekly per the label is the standard remedy. For sunburn or fluoride damage, no treatment helps — just remove damaged leaves and wait for new growth.
When this can't be saved
Most cases of geranium brown spots are recoverable, but a few red flags point to a plant that has gone past the point of return. If you spot any of these, consider propagating a clean cutting and starting over.
- Spots are spreading by several per day across multiple leaves — active aggressive disease.
- The whole crown of the plant is blackening from a central point outward.
- Healthy-looking neighbouring plants are starting to show the same symptoms.
Prevention
For geranium, the single biggest preventative is matching its native rhythm: water deeply, then let the top third of the pot dry, 6+ hours of direct sun for compact growth and flowers, and a free-draining pot with a working drainage hole. Water at the soil line, not the leaves, especially in the evening when leaves can't dry before nightfall. Switch to filtered or collected rainwater for sensitive species — it pays for itself in fewer crispy edges. Improve airflow around densely planted shelves with a small clip-on fan.
Common questions
Why is my geranium brown spots?
Geranium brown spots is most often caused by fungal or bacterial leaf spot. Remove the worst leaves, switch to filtered water if the species is tap-sensitive, and water at the soil line only.
What is the most common cause of geranium brown spots?
The most likely cause is fungal or bacterial leaf spot. Brown spots with yellow halos appearing on geranium, especially after water sat on the leaves overnight, are most often fungal or bacterial leaf spot. Remove affected leaves, water only at the soil line, improve airflow, and apply a copper fungicide if it spreads.
Why does this happen to geranium in particular?
Brown spotting on a Pelargonium has a few distinct signatures. Corky, raised tan bumps confined to leaf undersides are edema, a watering-and-humidity fault rather than a disease. Fuzzy grey-brown rot spreading over leaves and stems in cool, damp air is botrytis. Most serious are small water-soaked spots that dry to brown, or brown V-shaped wedges biting in from the margins - the mark of bacterial blight, which turns leaves yellow and can go on to kill the whole plant systemically.
How do I fix a geranium with brown spots?
Keep the leaves dry: water at the base, space plants so air moves between them, and clear fallen spotted leaves that harbour it. Pick off affected leaves with clean, dry hands. The one that changes everything is bacterial blight - the water-soaked spots and marginal wedges - because it lives inside the plant and travels in cuttings, so a blight-suspect geranium must be thrown out whole and never propagated from, however healthy its tips.
Is geranium brown spots normal, or a real problem?
Cold nights and strong sun flush a geranium's older leaves red or bronze - a pigment response, not rot, fading as warmth returns. The horseshoe zone natural here is likewise no blemish. Treat brown marks as trouble only when active: water-soaked spots drying to dead patches, wedges eating in from the margins, or fuzzy grey growth in damp weather, all spreading leaf to leaf rather than colouring evenly.
How do I prevent geranium brown spots?
For geranium, the single biggest preventative is matching its native rhythm: water deeply, then let the top third of the pot dry, 6+ hours of direct sun for compact growth and flowers, and a free-draining pot with a working drainage hole. Water at the soil line, not the leaves, especially in the evening when leaves can't dry before nightfall. Switch to filtered or collected rainwater for sensitive species — it pays for itself in fewer crispy edges. Improve airflow around densely planted shelves with a small clip-on fan.