Why are my tomatoes growing black on the bottom?

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Brock Ingham
Brock Ingham

After months of hard work and care the last thing you want to see on the bottom of your tomatoes is little black spots. One of the highlights of the summer is picking the seasons first formed juicy tomato, there is nothing quite like it. Yet, at times, you may notice your tomatoes may have an unsightly black patch on the bottom. Don’t worry. It’s a typical issue known as blossom end rot that’s simpler to resolve than you would imagine. So, if you have experienced black patches on the tomato’s bottom or wish to avoid them, this post is for you.

Black spots on tomatoes
Black spots on tomatoes

As the saying goes: “You will realize that those round, pinkish-red things that are available in the stores bear no resemblance at all to the real tomato.”

― Craig Lehoullier

Why do tomatoes grow black spots?

Blossom-end rot is a common disorder that results in black spots on growing fruit and is brought on by a calcium deficit. However, home gardeners must note that, at times, the condition is not due to a lack of calcium in the soil. Thus, calcium additions and sprays will not effectively resolve the issue. Rather, blossom end rot in tomatoes occurs when the plant fails to absorb calcium from the soil owing to excessive or insufficient watering, like drought, strong rainfall, or inconsistent watering.

Hence, blossom end rot is neither a bacterial rotting nor a disease. The black patches on the bottom of tomatoes may occur with little to no indication. It might occur during your first tomato harvest or at any moment throughout the season.

What does blossom-end rot look like?

Blossom-end rot appears initially as water-soaked areas on the blossom ending or base of the tomatoes. The damaged tissue starts to deteriorate fast, causing the affected region to appear sunken, dark brown or black, and leathery. This condition often happens midway through the fruit’s development and may arise both while the fruit is still greenish and once it has already started to ripen. There may also be white spots or stripes on the underside. Your thriving plant may not exhibit any additional symptoms except bottom-blackened tomatoes, although sometimes you may discover rotten tomatoes on the vines.

Blossom end rot
Blossom end rot

Can you stop blossom end rot once it starts?

If you see blossom end rot of any of your fruits, the condition is sadly irreversible. You will need to eliminate the damaged fruit and adjust your plant’s calcium levels for the subsequent fruit to develop normally.

If irregular watering is part of the issue, consider watering on a routine and adding mulch around your plants. You may also use a continual drip irrigation system to ensure a steady moisture level.

Typically, tomato end blossom rot will impact the first two fruiting cycles. Although blossom end rot may make a plant susceptible to disease, it is not communicable and will not spread to other fruits; thus, sprays and fungicides are unnecessary. Eliminating the problematic fruit and maintaining a regular watering schedule may resolve the issue for subsequent fruits.

How do you treat tomatoes with black bottoms?

Fortunately, blossom-end rot may be prevented. Adequate soil moisture is essential for avoiding this condition. Ensure that you routinely water your tomatoes during dry months. They require approximately one inch of water every week, and it is preferable to deliver the whole quantity at once through a gradual, constant soaking to the root zone. A small amount of water applied daily or every few days exacerbates the issue since it does not permeate the soil to hydrate the whole root zone. Please take into account that calcium in the soil is not always close to the roots of plants; it might have to traverse a distance with moisture in the soil to reach the plant.

In addition to watering regularly and appropriately, you may take many more measures to avoid blossom end rot.

  • Mulch promptly and adequately. Applying a layer of 2 to 3 inches of organic material to the soil’s surface surrounding your tomato plants at the beginning of the season maintains consistent soil moisture levels. You are also decreasing weed growth. Straw, untreated grass cuttings, and leaf mulch provide excellent mulch for tomato plants.
  • Ensure that the pH of your garden’s soil is as near to 6.5 as feasible. The optimal pH facilitates calcium absorption. Calcium and numerous other critical elements are more easily accessible to plants at this pH level.
  • Prevent over-fertilization, particularly with chemical fertilizers. As a result of the interference of excess ammonium ions, tomato plants supplied with ammonia-based nitrogen fertilizer are less able to absorb calcium.
  • Drip irrigation will assist prevent the soil from getting absolutely bone dry in the case of high heat.
Bunch of tomatoes with end rot
Bunch of tomatoes with end rot

What is the fastest way to add calcium to the soil?

Supplying calcium to the soil reduces blossom end rot, among the most terrible gardening diseases. Hence, to avoid this condition and have good tomatoes, home gardeners must ensure enough supply of calcium in the soil. There are several techniques to add calcium to garden soil, depending on the soil’s condition. It is best to begin with a healthy soil base, then add calcium fertilizer as necessary. Consider these approaches.

1. Foliar spray:

A quick and convenient way to add calcium is through a spray comprising calcium acetate, chloride, or calcium nitrate. This approach is effective and fast-acting on plants with an evident and severe calcium deficit. In the event of sprays, plant leaves immediately absorb calcium.

2. Lime:

Calcium carbonate, sometimes known as lime, is an excellent source of calcium that you can add to your soil, yet we must avoid excessive application. Remember that it will increase the soil’s pH. Dolomitic lime includes magnesium and might be advantageous if your soil possesses low magnesium levels.  

3. Bone Meal:

Made from animal bones that have been broken up, bone meal is an excellent soil supplement that may increase the calcium in the soil. Bone meal increases calcium levels progressively throughout a whole growing season.

4. Gypsum:

This type of calcium sulfate is an excellent addition if soil pH is an issue; unlike many other supplements, gypsum is pH neutral.

Milk powder is a reliable solution to eliminate blossom end rot in tomato plants, keeping them healthy and safe and bringing in a much larger and more abundant harvest.

5. Wood Ashes:

Wood ash from hardwoods is beneficial for soil improvement. Consider that wood ash will, however, increase the soil’s pH.

6. Eggshells:

Eggshells are a slower method of adding calcium to soil than bone meals since they must decompose before plants can use them. You may add eggshells to the soil while planting seedlings, add eggshells to manure and then add the finished compost to the soil, or apply eggshells directly to the soil.

Eggshell fertilizer
Eggshell fertilizer


Does powdered milk help blossom end rot?

Blossom end rot occurs when the plant cannot transport sufficient calcium to all of its components with water. As milk and other dairy products include substantial amounts of calcium, they are excellent for the general development of plants. Make careful to blend the milk powder with water to aid soil absorption.

What does Epsom salt do for tomatoes?

Magnesium and sulfur are micronutrients found in Epsom salt. The cultivation of tasty tomatoes depends on various conditions, including a good soil micronutrient intake. By introducing magnesium and sulfur to the soil, some gardeners may discover that Epsom salt enhances the taste. When cultivating tomato plants, the taste cannot be overlooked.

A strong supply and equilibrium of all micronutrients — particularly magnesium and sulfur — are crucial for plant development, making your tomatoes more flavorful.

Final Thoughts

A water-soaked black patch characterizes blossom-end rot at the blossom end of tomatoes. Despite the rather unsettling name, it is neither a disease nor triggered by a pathogen. In actuality, it is triggered by a calcium deficit, owing mostly to the vitamin not reaching the tomatoes even though the plant has enough calcium. Yet, with these techniques, you can always prevent the issue and grow healthy tomatoes.

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