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Black Bottom Tomatoes: What’s the Cause and How to Fix it


You head out into the garden to check the progress of your prized tomatoes only to find dark waterlogged spots on the bottom of the fruit. You then check your zucchini and notice the blossom end of the small fruit has shriveled and turned brown. Don’t panic!  While your plants are suffering from a disease, there is a simple and effective solution.

Blossom End Rot

Your plants have blossom end rot, which can affect not only tomatoes but squash, melons and peppers. Symptoms often include:

  • Lots of flowers but no fruit
  • Fruit begins to grow but then withers and dies
  • Blossom end of fruit turns brown/black.
  • Dark sunken lesions form on the blossom end of fruit

Blossom end rot is caused by a calcium deficiency. Calcium is important to a plants cell development. A lack of calcium causes cells to be weak and unable to contain their contents. In plants this results in dark, watery, soft spots on the fruit. A calcium deficiency in plants can happen two ways, either the soil lacks calcium or the plant is unable to absorb the calcium in the soil.

Uneven watering can hinder a plant’s ability to take in calcium. To make sure your plants are getting a consistent amount of water and enough water try watering on a schedule. To do this use a sprinkler system, soaker hoses, or a watering blanket set on a timer. This way your plants get a nice slow soak at regular intervals. Nitrogen helps plants put out tons of flowers, but can also cause plants to not be able to absorb calcium. To prevent this avoid applying fertilizer or compost tea high in nitrogen once plants are established.

If lack of calcium in the soil is the issue there are many ways to get calcium to your plants to help them grow large healthy fruits. One of the most traditional methods is to apply lime to the soil. Lime is made from crushed limestone and is naturally high in calcium and magnesium. Lime also has the added benefit of promoting better air and water flow in the soil, perfect for those with heavy clay soil.

Another method of adding calcium to your soil is by side dressing with a calcium rich fertilizer such as Dr. Earth’s Organic Fish Bone Meal. Fish Bone Meal is an organic source of calcium and phosphorous and Dr. Earth products have the added advantage of seven beneficial soil microbes. Dr. Earth’s Organic Fish Bone Meal can also be used to create a nutrient rich compost tea.

The up side of blossom end rot is that it doesn’t really harm the plant just the fruit. This means by properly identifying and treating the problem you can still have a great harvest this season.

Are your tomato or other vegetable plants suffering from pests or disease? Comment below or email us at gardenadvice@mastergardening.com