Why Are My Tomato Leaves Turning Yellow? 5 Causes & Fixes (2026)
クイック回答
Remove yellow leaves immediately and check for overwatering — the #1 cause. If yellowing starts from the bottom, it’s likely nitrogen deficiency (apply balanced NPK fertilizer). If yellowing has brown spots, suspect early blight (apply copper fungicide every 7–10 days). Water at the base, never on leaves, and ensure 6+ hours of sunlight daily.
どのように見えますか？
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Early stage
Lower leaves develop pale yellow patches, especially between veins. Plant still looks mostly healthy from above.
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Advanced
Yellowing spreads upward. Affected leaves develop brown edges or spots. Some leaves begin to curl and drop.
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Severe
Majority of foliage is yellow or brown. Plant is stunted. Fruit production drops significantly. Stems may show discoloration.
治療方法
Apply compost tea or fish emulsion fertilizer
Mix fish emulsion at 1 tablespoon per gallon of water. Apply to soil around the base of each plant, not on leaves. This provides a quick nitrogen boost.
タイミング: Every 2 weeks during growing season
Add 2–3 inches of organic mulch
Straw, wood chips, or shredded leaves. Mulch conserves moisture, regulates soil temperature, and slowly adds nutrients as it decomposes.
タイミング: Once at planting, refresh mid-season
Spray neem oil for fungal infections
Mix 2 teaspoons neem oil + 1 teaspoon liquid soap per liter of water. Spray on affected leaves in the early morning or evening, covering both sides.
タイミング: Every 7 days until symptoms improve
Epsom salt foliar spray for magnesium
Dissolve 1 tablespoon Epsom salt (magnesium sulfate) in 1 liter of water. Spray directly on leaves for fast absorption.
タイミング: Every 2 weeks if interveinal chlorosis present
最適：小規模農家、有機認証、家庭菜園
Balanced NPK fertilizer (10-10-10)
Copper-based fungicide (Bordeaux mixture)
Mancozeb 75% WP
最適：大規模農業、深刻な発生
Water at the base, never overhead
Drip irrigation or hand-watering at soil level prevents fungal spores from splashing onto leaves. Wet foliage is the #1 disease invitation.
Ensure proper spacing (60–90cm between plants)
Good air circulation lets leaves dry quickly after rain or dew, dramatically reducing fungal disease risk.
Rotate crops — don’t plant tomatoes in the same spot for 3 years
Soil-borne diseases like Fusarium and Verticillium survive in soil for years. Rotation breaks the disease cycle.
Test soil pH and maintain 6.0–6.8
Most nutrient deficiencies occur because soil pH locks nutrients away from roots. A simple pH test reveals the real problem.
最良の治療は予防です
この問題が発生するとき
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気温
18–28°C (cool to warm)
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湿度
Above 70% increases fungal risk
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降雨量
Frequent rain worsens blight and wilt
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季節
Mid to late growing season
Tomato農家向け
For tomato farmers: choose varieties with 'VFN' resistance labels (Verticillium, Fusarium, Nematode resistant). In tropical regions, grow heat-tolerant varieties like 'Tropical Ruby' or 'Heatmaster'. Always stake or cage plants to keep foliage off the ground. Remove the lowest 12 inches of leaves once plants are established — this prevents soil-splash infections.
農家もよく尋ねる質問
Can yellow tomato leaves turn green again?
No. Once a leaf has turned fully yellow, it won’t recover. Remove it to redirect the plant’s energy to healthy growth. However, new leaves will grow green if you fix the underlying cause (nutrient deficiency, watering issue, or disease).
Should I remove yellow leaves from my tomato plant?
Yes, always. Yellow leaves are either nutrient-depleted or diseased. In both cases, removing them helps the plant focus energy on fruit production and prevents disease from spreading to healthy foliage.
Is it normal for bottom leaves to turn yellow?
Some lower leaf yellowing is normal as the plant matures and directs energy to fruit. But if more than 2–3 bottom leaves are yellow at once, it usually indicates nitrogen deficiency or early blight — both treatable.
How do I tell if yellowing is from overwatering or disease?
Overwatering: leaves turn uniformly pale yellow, feel soft/limp, soil is constantly wet. Disease: yellowing has distinct patterns — brown spots (blight), one-sided yellowing (wilt), or yellowing between veins only (deficiency).
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