Blossom End Rot on Tomatoes: Causes and Fixes

Tomatoes turning black on the bottom aren't really rotten

rot on tomatoes

The Spruce / K. Dave 

Nothing compares to the taste of vegetables picked fresh from your garden and homegrown tomatoes are one of the best. Tomatoes grow on vines, and like many vines, the tomato plant grows rapidly. These plants can be troubled by blights, infections, and voracious insect pests. One problem you are likely to run into that sounds much worse than it is: blossom end rot.

When tomatoes reach the half-grown stage, fruits that may seem fine otherwise begin to develop hard brown spots on the bottom. These gradually grow in size and turn leathery and black by the time the fruit ripens into redness. This symptom, which can also occur in related members of the nightshade family, such as peppers and eggplants, is usually a condition known as blossom end rot (BER), sometimes referred to as tomato blossom end rot or tomato end rot.

 Problem Type  Plant Disease
 Affected Plants  Tomatoes, Peppers, Eggplants, Zucchini

What Is Blossom End Rot?

Despite the name, blossom end rot is not a bacterial rot, nor is it a disease. It is a condition caused by a calcium deficiency in the plant when the fruit is forming and will often resolve itself as additional fruit begins to set. Calcium is the nutrient necessary for forming the skin of the fruit. Deformity results when the plant is unable to deliver the necessary calcium at the crucial phase of growth.

The first sign is a light brown discoloration near the bottom of the fruit. These spots grow and darken until they cover up to half of the tomato and dark sunken craters form. It will look like the tomatoes are rotting on the vine.

If you're growing indeterminate tomatoes (those that set fruit all season) and you have a few tomatoes with blossom end rot, it doesn't mean that all your tomatoes will be affected. Even without treatment, most of your later season tomatoes will likely be fine.

first signs of blossom end rot
The first sign of blossom end rot

The Spruce / K. Dave

bottom of tomatoes rotting
Later stage blossom end rot

The Spruce / K. Dave

Causes of Blossom End Rot in Tomatoes

Although calcium deficiency is what causes blossom end rot, it is fairly rare for this to be caused by soil that is lacking in calcium. Instead, the lack of calcium is a result of various environmental conditions that prevent the plant from taking up and transporting the necessary calcium.

In precise terms, there are two main reasons for blossom end rot:

  • The plant grows so fast due to over-fertilization during early fruiting that it is unable to take up sufficient amounts of calcium to keep up with the fruit development.
  • Stress factors render the plant unable to process the calcium the plant does take up from the soil. The stress is most commonly due to improper watering, particularly in container gardening. If the soil gets too dry, the plant doesn't get the calcium it needs to produce healthy fruit. If the plant gets too much moisture, the same thing can happen.

3 Ways to Fix and Prevent Blossom End Rot

  1. Remove Affected Tomatoes

    If you have tomatoes with blossom end rot on your plants, remove the damaged tomatoes as soon as you detect the problem. They will keep growing and use the plant's energy, which is better put to use producing new rot-free fruit.

  2. Improve Your Watering Routine

    • Your best bet for treating blossom end rot is to adjust your watering to make sure you are using good watering practices. 
    • Don't let your tomato plants dry out; keep the soil moist, but not wet.
    • Water your plants at ground level and avoid overhead watering as this can invite soil-borne disease that weakens the overall plant and affects both growth and yield.
  3. Add Mulch

    Mulching tomatoes helps to conserve moisture in the soil. Use organic mulches such as straw free of weed seed, grass clippings, peat moss, or wood chips.

    watering tomato plants
    The Spruce / K. Dave 


    Some tomato varieties, particularly Roma types, are more susceptible to blossom end rot due to rapid growth and high yields.

How to Help Prevent Blossom End Rot

While adjusting feeding and watering rates to levels that encourage steady, moderate growth of the plant can somewhat reduce the occurrence of blossom end rot, it is difficult if not impossible to prevent it entirely, since garden conditions are so variable. There are several ways to prevent blossom end rot from happening in the first place.

using spray on tomato plants

The Spruce / K. Dave  

  • Plant tomatoes in the right soil. Soil that is well-drained and adequately amended with organic material, such as compost or peat moss, makes it easier for the roots to take up the crucial calcium as the fruit is just developing.
  • Test soil pH. Most vegetables do well in soil with pH levels of 6.2 to 6.8, but vegetables prone to blossom end rot need a pH level of at least 6.5, which frees up more calcium in the soil. If a soil test indicates a pH level that is too low (too acidic), take measures to raise the pH level. Working fast-acting agricultural lime into the top 12 inches of soil is a good way to do this.
  • Plant at the right time. Gardeners that are too eager often put their tomatoes in the ground when the soil is still too cold for the roots to adequately develop. This again deprives the plant of calcium at the critical growth period. If you are growing seedlings, harden them off slowly with gradually increasing periods of outdoor exposure before subjecting them to soil conditions.
  • Fertilize plants properly. Don't overfertilize with a high-nitrogen fertilizer that accelerates the development of leaves and diverts energy away from fruit development. But don't under-fertilize. Tomatoes are heavy feeders, and potting soil, unless it is pre-fertilized, doesn't provide all the nutrients tomatoes need.
  • Use mulch around plants. This can help retain moisture in the soil, allowing for a steadier growth rate that makes blossom end rot less likely to occur.
  • Use a calcium spray solution. Commercial calcium spray products applied directly to the plants two or three times a week when the blossoms first appear may supply tomatoes with the calcium they need. However, the effectiveness of this treatment is limited.
  • Add Epsom salts at planting time. Dig a fairly deep hole and remove the seed leaves and lowest leaves of the plant. Tomatoes need to be planted deep with about a third of the plant buried in the soil. Mix 1-2 tablespoons of Epsom salts into the soil used to fill the planting hole. This allows the plant to establish a good root system with early uptake of nutrients for consistent growth.
  • How do you fix blossom end rot?

    There are three ways to fix blossom end rot once it begins. 1) Remove the affected tomatoes so no more plant energy is wasted. 2) Improve your watering routine. 3) Add mulch around the plants so that soil moisture is retained.

  • What are the main causes of blossom end rot?

    Over-fertilization of the tomato plant during early fruiting causes it to grow so rapidly that it is unable to take up sufficient amounts of calcium to keep up with the fruit development. Also, stress due to improper watering impedes the plant's ability to absorb the calcium it needs to produce healthy fruit.

  • Can overwatering cause blossom end rot?

    Yes—but so can under-watering. Use good watering practices and don't let tomato plants dry out; keep the soil moist, but not wet. Water your plants at ground level and avoid overhead watering as this can invite soil-borne disease that weakens the overall plant and affects both growth and yield.

Originally written by
Kerry Michaels

Kerry Michaels is a container gardening expert with over 20 years of experience maintaining container gardens in Maine. She specializes in writing and capturing photography for gardening and landscape design for print and broadcast media, including the Discovery Channel, Small Gardens, and Disney, among others.

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  1. Blossom-end rot tip sheet. Michigan State University Extension

  2. Prevent Blossom End Rot in Tomatoes. University of Georgia Tattnall County Extension