Potassium deficiency on tomato
A physiological disorder that shows up mainly during heavy fruiting, when the tomato uses huge amounts of potassium to build and color its fruit. The classic tomato symptom is uneven ripening — green or yellow patches left on an otherwise red fruit.
Symptom photos
Symptoms
- Older, lower leaves drying and browning around the edges (marginal scorch)
- Leaves curling downwards and turning brittle
- Uneven ripening — green or yellow patches near the stalk on a ripe fruit
- Hard, white strands inside the flesh
- Poorly colored fruit with less flavour and lower sugar content
- Reduced tolerance of drought, cold and disease
What it does to the crop
- A clear drop in fruit quality and flavour
- Blotchy fruit that cannot be sold
- Weakened plants that are more prone to fungal disease
What encourages it
- Light, sandy soils low in potassium
- Heavy, prolonged cropping that drains potassium reserves
- Too much nitrogen at the expense of potassium
- Excess calcium or magnesium interfering with potassium uptake
- Uneven watering restricting movement of the nutrient
Prevention
- Increase potassium feeding from the time the first trusses set
- Use potassium sulphate rather than muriate of potash (tomatoes dislike chloride)
- Foliar feed with potassium at the first signs on the fruit
- Keep soil moisture even
- Balance nitrogen against potassium — fruiting plants need more potassium
⚠️ Before you reach for a spray
This atlas is informational and still growing — different diseases can look almost identical. Confirm the diagnosis and read the product label before applying any plant protection product. If you are unsure, ask your local extension or advisory service.
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