Why Do Tomatoes Turn Black on the Bottom While Growing?

Tomato plants that develop black lesions have contracted blossom-end rot, a physiologic disorder caused by low nutrients in the fruit and lack of adequate moisture. If you give your tomatoes proper care and prepare the garden for your crop, you're less likely to encounter this condition.

  1. Significance

    • When tomatoes develop black spots on the bottom, they have developed blossom-end rot. The tomatoes cannot be eaten, so gardeners should clip them off the plant to prevent the problem from spreading. Peppers and eggplants can contract the same disorder. Gardeners could lose up to half their tomato crop from blossom-end rot in some years, according to Ohio State University Extension Service.


    • The black spots starts out as a watery lesion near the end of the tomato, which can appear on either green or red fruits. The watery spot sinks into the fruit and turns black and can grow halfway up the affected fruit. Once you've noticed the initial symptoms, there's nothing you can do to reverse damage in infected fruit.


    • Tomato plants tend to develop blossom-end rot when they receive uneven amounts of moisture. For example, plants that go from being too dry to too wet, then back, are susceptible to the disease. To prevent this, water your tomatoes regularly. Removing affected fruit can prevent blossom-end rot from spreading to new tomatoes. Tomato plants need 1 inch of water per week, on average.


    • Plants grown in calcium-depleted soil are also likely to develop this condition. Ohio State University horticulturists note that adding calcium directly to the soil doesn't really help, because it's too challenging for the fruit to absorb this. Maintaining soil pH around 6.5 will give you a naturally calcium-rich soil. Using nitrate nitrogen instead of ammonium-derived nitrogen to fertilize the tomatoes also helps keep calcium levels up to ward off blossom-end rot.

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