What to check first

Locate the damaged area

Turn the fruit over: the blossom end is opposite the stem. Blossom-end rot commonly starts there as a small water-soaked area that becomes dark and flattened. Spots scattered elsewhere, particularly on ripe fruit, need a different assessment. Take a photo showing the whole fruit as well as the lesion. [1] [3]

Compare fruit and weather

Record whether the first developing tomatoes were affected after a dry spell, heavy rain, or hot weather. Blossom-end rot often appears on early fruit. That pattern is useful evidence of interrupted calcium delivery; it is not a laboratory test of your soil. [1]

Check moisture where roots grow

Feel below the surface before watering and compare the center and edge of a container. Repeatedly drying out and then flooding the root zone is more informative than a dry-looking soil crust. Review whether an irrigation timer kept running through rain. [2]

Review recent feeding and digging

Note fertilizer products, application dates, and any hoeing close to the stem. Excess nitrogen and root injury can contribute. A soil test is a better basis for correcting a genuine calcium or pH problem than adding amendments to every plant with damaged fruit. [1]

Choose the next step for your plant

Make moisture more consistent

Water the root zone according to its moisture and drainage, rather than compensating for missed watering with repeated soaking. Mulch can reduce fluctuations. For a container, make sure drainage works and increase how often you inspect it during hot, windy weather. [2]

Judge the next fruit

Remove badly affected tomatoes; the damaged area will not repair. Keep healthy foliage and roots intact, and avoid extra fertilizer while you establish the cause. Compare later fruit with this first group instead of treating persistent marks on old tomatoes as a failed recovery. [1]

What to avoid

  • Do not assume calcium fertilizer will solve a moisture or root problem.
  • Avoid deep cultivation close to tomato roots.
  • Do not spray a fungicide simply because the damaged patch is dark.

What to watch next

Mark which fruit were already affected and check newly developing fruit over the following weeks. Keep a short rain, watering, and fertilizer record. If damage spreads beyond the blossom end, has unusual growth, or accompanies wilting plants, send photographs and that history to your local Extension office before choosing treatment.

Common questions

Is blossom-end rot contagious?

Blossom-end rot itself is a physiological disorder, not an infection moving between plants. However, microorganisms can colonize the damaged tissue, so a decaying tomato may have more than one problem. [1] [3]

Can a well-watered plant still get it?

Yes. Moisture earlier in fruit development, damaged roots, rapid growth, and nutrient balance can matter. Seeing moist soil today does not establish what the developing fruit experienced previously. [1] [2]

Sources and review

This guide was prepared with AI assistance and checked against the sources below. It has not been reviewed by a botanist. Conditions and plant responses vary; use the checks above to decide what applies. Read our editorial standards.

  1. University of Minnesota Extension: Tomato disorders

    Blossom-end symptoms, calcium transport, moisture and root stress, nitrogen, and removal of damaged fruit.

  2. University of Minnesota Extension: Irrigation strategies for vegetables

    Stable soil moisture and calcium delivery; calcium may be present in soil when blossom-end rot occurs.

  3. University of Minnesota Extension: Tomato fruit rots

    Location and appearance distinguish blossom-end rot from other tomato fruit damage.