Blossom-end rot usually starts as a water-soaked area at the blossom end of a tomato, opposite the stem. It can develop into a dark, sunken patch. It is a physiological disorder involving inadequate calcium reaching the developing fruit, rather than a contagious disease.
Why it happens
Uneven moisture, root damage and rapid growth can interfere with calcium movement even when calcium is present in the soil. Excess nitrogen can contribute. Adding more calcium without checking the growing conditions may miss the cause.
Protect the next fruit
- Keep root-zone moisture consistent and maintain drainage.
- Mulch appropriately to reduce swings between wet and dry soil.
- Avoid damaging roots when cultivating near plants.
- Use a soil test and fertilizer guidance instead of adding amendments by guesswork.
The damaged part of an existing tomato will not heal. Improving care can help later fruit develop normally. Inspect container plants especially often because their growing medium can dry quickly.
Can an affected tomato be eaten?
When the problem is truly blossom-end rot and the rest of the tomato is otherwise sound, Extension guidance allows cutting away the affected area for fresh use. That does not apply to every tomato with a black spot. Mold, spreading decay, leaking or uncertainty about the diagnosis are reasons to discard the fruit rather than assume it is edible.
Use sound tomatoes for canning
The National Center for Home Food Preservation recommends firm, disease-free tomatoes for canning. Do not use this article as permission to can damaged or decaying fruit. Follow a tested recipe, including required acidification and the correct processing method.
If lesions do not match blossom-end rot, send clear photos to your local Extension office before treating the plants. A correct diagnosis helps you choose useful care instead of repeatedly applying unnecessary products.
