Why does my begonia have brown spots?

The 4 most likely causes

The cause of begonia brown spotsusually 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.

1. Low humidity (Likely)
   Begonia is native to humid environments and struggles when household humidity drops below 40%. The first sign is crispy brown leaf tips, followed by pale, curling foliage. A humidifier, a pebble tray, or grouping plants together raises local humidity meaningfully.
2. Fluoride or chlorine in tap water (Likely)
   Begonia is sensitive to the fluoride and chlorine added to most municipal water supplies. Minerals build up at the leaf tips and cause crispy brown edges or speckled spots. Switch to rainwater, filtered water, or tap water that has sat uncovered for 24 hours so the chlorine can off-gas.
3. Fungal or bacterial leaf spot (Possible)
   Brown spots with yellow halos appearing on begonia, 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.
4. Sunburn or intense direct sun (Possible)
   Bleached patches, papery brown spots, or crisped leaf surfaces on the south-facing side of begonia 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.

Why begonia in particular

Rex begonias are unusually prone to fungal and bacterial leaf spotting because their soft, hairy leaves hold moisture against the surface. Cool, damp, still air brings botrytis as fuzzy grey-brown patches, while water sitting on the foliage invites bacterial spots ringed with a yellow halo. Their love of humidity works against them here, so the tell is spots that appear after misting or splashing rather than the dry, evenly scattered marks you would blame on sun or minerals.

Normal turnover, or real trouble?

Half the point of a Rex begonia is its patterning, and the swirls of silver, plum and near-black that follow the leaf's spiral can be misread as damage, as can the red, hairy leaf backs. True colour sits in symmetrical bands that trace the leaf's design. A brown spot is different: it is an irregular dead patch that cuts across the pattern, often sunken or ringed, and it will spread rather than stay put.

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 begonia usually mean low humidity or tap-water minerals.

The fix — step by step

The first move is to dry the plant out and open it up: stop all misting and overhead watering, pick off the worst-spotted leaves and bin them rather than compost them, and get gentle air moving across the foliage with a small fan. Space it so leaves are not pressed against neighbours. Water only from below from now on. Wet, crowded, still air is what let the spots start, so reverse each of those.

This is the recovery sequence Growli walks users through for begonia with brown spots. Work through the steps in order; skipping ahead is the most common reason a plant fails to bounce back.

1. Quarantine if you suspect disease. If spots look wet, are spreading, or have a yellow halo, move begonia away from your other plants until you have a diagnosis. Disinfect your tools between plants.
2. 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.
3. 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.
4. Improve airflow and watering technique. Water at the soil line only — never on the leaves. Space begonia so leaves are not touching neighbouring plants. A small fan in stagnant rooms makes a surprising difference.
5. 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 begonia 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 begonia, the single biggest preventative is matching its native rhythm: when the top 2-3cm of soil is dry, every 5-7 days, bright indirect light, 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

Related guides

• PictureThis alternatives — 7 plant ID apps compared
• Is begonia toxic to cats and dogs? — toxic to pets, per the ASPCA
• How often to water begonia — the watering brief
• When to repot begonia — pot size and timing
• Brown spots on plants — the full diagnostic guide across species
• What's wrong with my plant? — Growli's flagship diagnosis index
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