A dark patch under a tomato: check moisture before adding calcium
Bed & Balcony · Care observation sheet · 2026-10-20

A first check for a tan-to-dark patch at the end opposite the stem. This is an observation guide, not a diagnosis from a description or photo.

OBSERVATIONS
Plant/cultivar and location:
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Patch position relative to stem:
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First affected fruit cluster and stage:
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Drainage and moisture history:
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Fertilizer used and any soil-test result:
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Later fruit condition and changes made:
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CHECKS
If a flattened patch is centered opposite the stem: Record whether the fruit was still enlarging. This pattern can fit blossom-end rot; compare it with the linked extension examples.

If the pale patch is on the sun-facing side: Record exposed fruit and any recent leaf removal. Location matters; do not label all fruit blemishes as blossom-end rot.

If leaves, stems or many fruit surfaces are also changing: Document the wider pattern. Seek a local plant adviser if there is rapid spread or the signs do not match a simple fruit disorder.

ACTION CHECKLIST
[ ] 1. Inspect before amending
Look at several fruit on the same plant. Note the first affected cluster, container size, drainage and recent fertilizer. Keep the plant label or packet so the record includes the actual cultivar.

[ ] 2. Make root care consistent
Check soil moisture regularly and use mulch where suitable to reduce large swings. Avoid digging close to the roots. Base additional fertilizer on the growing medium, product instructions and a relevant soil test rather than on the fruit patch alone.

[ ] 3. Watch later clusters
Remove affected fruit that will not develop normally, following local disposal guidance. Keep records of later fruit: a plant can produce unaffected fruit after an early affected cluster. Record changes one at a time where practical.

NEXT CHECK
At the next care visit, record moisture and the state of a newly developing cluster. Bring the photos, cultivar name, fertilizer details and watering history to a local adviser if the problem persists.

REFERENCE
University of Minnesota Extension: Tomato disorders
https://extension.umn.edu/garden-and-home/yard-and-garden/gardening-in-minnesota/yard-and-garden-problems/tomato-disorders
University of Minnesota Extension: Tomato fruit spots
https://apps.extension.umn.edu/garden/diagnose/plant/vegetable/tomato/fruitspots.html

Your notes stay in this file. Review local conditions before acting.