Recognizing and correcting potassium deficiency in tomatoes
Brown edges on tomato leaves, mainly appearing on the lower leaves, are a typical sign of potassium deficiency. The symptoms may look dramatic at first glance, but they are clearly identifiable and can be addressed in a targeted way.
Typical symptoms of potassium deficiency in tomatoes:
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Yellowish to brown discoloration along the leaf edges
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Leaf margins appear scorched or dry
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Necrosis begins at the edges and gradually moves inward
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Leaf veins remain green for a long time, while the tissue between them discolors first
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Symptoms usually appear first on older, lower leaves
The deficiency develops gradually. If the underlying causes are not corrected, it can lead to stunted growth, poor fruit development, or fruit cracking.
Causes of potassium deficiency
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Imbalance in nutrient supply, e.g. too much nitrogen and too little potassium
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Depleted soils or nutrient-poor potting substrate
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Heavy-feeding varieties or a high fruit load
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Irregular watering, which disrupts nutrient uptake
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In container growing: limited root space = faster nutrient depletion
Potassium is a mobile nutrient that the plant redistributes from older leaves to younger parts when it is in short supply. This is why symptoms first appear on the lower leaves.
Corrective measures for potassium deficiency
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Remove damaged leaves – they will not recover
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Apply a potassium-rich liquid fertilizer (e.g. tomato fertilizer with an NPK ratio of 6-3-10 or similar)
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Alternatively: comfrey liquid manure or wood ash (use sparingly) as natural potassium sources
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Water regularly and evenly, avoiding waterlogging
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Avoid excessive nitrogen fertilization – maintain a balanced nutrient ratio
Existing damage will remain visible, but plant growth should stabilize. New leaves will then emerge healthy again.
Potassium deficiency is not uncommon in tomatoes—especially under heavy fruit load or when grown in containers. The symptoms are clear: brownish leaf edges on older leaves. If addressed in time, the deficiency can be easily corrected without affecting the harvest.