Journal/Vegetable Garden · 7 min
Tomato Problems: A Visual Diagnosis Guide
Blossom end rot, cracks, curl, blight and yellow leaves — how to tell them apart and fix them fast.
Quick answer
Most tomato problems trace back to three causes: uneven watering (blossom end rot, cracking, curl), poor airflow (blight, mildew), or hunger (yellowing lower leaves). Mulch heavily, water deeply twice a week, and feed weekly once flowers open.
Tomatoes complain loudly. Once you learn to read the symptoms, you can usually correct course before you lose the crop.
Symptom checker
Common tomato symptoms and causes
| Symptom | Likely cause | Fix |
|---|---|---|
| Black leathery patch on bottom of fruit | Blossom end rot — uneven water uptake | Mulch and water evenly; not a calcium deficiency |
| Fruit cracking on top | Heavy rain after a dry spell | Mulch and keep soil steady |
| Leaves curling upward | Heat stress or over-pruning | Afternoon shade above 30°C |
| Yellow lower leaves | Nitrogen shortage or overwatering | Feed weekly with tomato food; check drainage |
| Brown spreading patches on leaves + stems | Late blight | Remove foliage, harvest fruit, destroy debris |
| Fine webbing under leaves | Spider mites | Rinse with water; increase humidity |
How to prevent 90% of it
- Mulch 5 cm deep with straw or compost.
- Water at the base twice a week, deeply — not lightly every day.
- Feed with a high-potash tomato food once flowers open.
- Prune the lowest leaves so they don't touch the soil.
- Rotate — never grow tomatoes in the same soil two years running.
Frequently asked questions
Is blossom end rot a calcium deficiency?
Not usually. The calcium is there in the soil — inconsistent watering stops the plant taking it up. Adding calcium rarely helps; even watering does.
Can I save a blighted tomato plant?
No. Remove it, bag it (don't compost) and harvest any healthy fruit early to ripen indoors. Blight spreads fast.
Why do my tomato leaves look silver and speckled?
Spider mites. Rinse the plant, raise humidity, and check under leaves for tiny moving dots.
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