Why does my kale have brown spots?

The 4 most likely causes

The cause of kale 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.

1. Fungal or bacterial leaf spot (Possible)
   Brown spots with yellow halos appearing on kale, 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.
2. Sunburn or intense direct sun (Possible)
   Bleached patches, papery brown spots, or crisped leaf surfaces on the south-facing side of kale 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.
3. Overwatering or poor drainage (Likely)
   In most homes overwatering is more often a drainage problem than a frequency problem. Kale needs a pot with a drainage hole, a chunky free-draining mix, and a watering rhythm of about 1-1.5 inches of water per week, evenly. Soggy soil drowns the roots and the first symptom you see above ground is yellowing or wilting foliage.
4. 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 kale in particular

Brown spots on kale usually name a specific fungal disease if you read their shape. Circular brown-to-grey lesions marked with concentric rings, like a small target, often ringed by a yellow halo, are Alternaria leaf spot, favoured by warm, wet weather on these broad leaves. Angular yellow-to-brown patches bounded by the leaf veins, with a greyish fuzz on the underside in damp air, are downy mildew instead. Both spread by splashed water and lingering leaf wetness, so watering the soil rather than the foliage slows them.

Normal turnover, or real trouble?

An outdoor leaf crop collects cosmetic marks that are not disease: tiny pale shot-holes from flea beetles peppering the leaf, ragged edges from caterpillar chewing, and weathering blemishes on the toughened outer leaves. These stay small and don't develop. The spots that matter grow and organise, circular brown lesions ringed like a target and haloed in yellow, or angular patches boxed in by the veins, because those are fungal infections that spread leaf to leaf.

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 kale usually mean low humidity or tap-water minerals.

The fix — step by step

Because kale's leaf spots spread in splashed water and lingering wetness, start by picking off and binning the worst-marked outer leaves rather than composting them; the clean inner leaves are what you eat anyway. Then switch to watering the soil, never the foliage, and thin or space crowded plants so leaves dry quickly after rain. A mulch stops spores splashing up from the ground, and next season move brassicas to a fresh bed.

This is the recovery sequence Growli walks users through for kale 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 kale 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 kale 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 kale 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 kale, the single biggest preventative is matching its native rhythm: about 1-1.5 inches of water per week, evenly, 6+ hours of sun, tolerates part shade, 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

• What's wrong with my plant? — the diagnosis apps compared
• Is kale toxic to cats and dogs? — mildly toxic to pets, per the ASPCA
• How often to water kale — the watering brief
• When to repot kale — 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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• Kale — curling leaves
• Kale — drooping
• Monstera — brown spots