Tomatoes Rotting at the Bottom? (Blossom End Rot Explained)

Tomatoes are a popular and easy-to-grow vegetable in a home garden. However, a common problem is tomatoes rotting at the bottom. If you’ve experienced this, you’ll know the tomato fruit looks perfectly normal on top but turns black and mushy at the bottom, making it inedible. So let’s find out the cause of the bottoms rotting on tomatoes and how to fix the problem.

Tomatoes Rotting on the Bottom: Blossom End Rot
Tomatoes Rotting on the Bottom: Blossom End Rot

Why Are My Tomatoes Rotting at the Bottom?

Tomatoes rotting at the bottom is due to Blossom End Rot which is caused by a calcium deficiency, often due to incorrect watering, poor soil condition, over-fertilization, and environmental stress. 

Let’s delve into each cause of Blossom End Rot with detailed solutions to help you prevent this problem from happening.

What is Blossom End Rot? 

Before diving into what causes blossom end rot and how to fix it, it would be helpful to know what it is and looks like. 

Blossom End Rot, or bottom rot, is a physiological disorder that affects tomatoes, causing the bottom of the fruit to become black, mushy, and hollow, rendering the fruit inedible.

The condition is caused by a calcium deficiency in the plant, which leads to a breakdown of cells in the cell walls, which causes the bottom end of the fruit to rot. 

When a calcium deficiency occurs in the tomato plant, it means the roots cannot carry calcium from the ground to the fruits. If you fix what is causing the calcium deficiency in the plant, the next fruit it produces should be rot-free. 

What Does Blossom End Rot Look Like?

Tomatoes Rotting on the Vine Blossome End Rot
Tomatoes Rotting on the Vine Blossom End Rot

The symptoms of Blossom End Rot usually appear when the first fruits to develop on the plant are still green, but they can also occur later in the growing season. 

Blossom End Rot can be a bit hidden at first. I’ve grown some beautiful-looking tomatoes that looked perfectly healthy from the top tomato, only to later discover, they were in fact affected by Blossom End Rot. It was only once I lifted them up that I discovered they were actually rotting at the bottom.

Have a look at the below photo which look like healthy tomatoes. They are actually the same tomatoes as shown in the photo above with Blossom End Rot!

Tomatoes Growing on the Vine
Tomatoes Growing on the Vine

Initially, a water-soaked spot appears on the blossom end of the fruit, which can grow in size and become hollow and black as the fruit matures. The affected area is usually dry and leathery. 

Fruit affected by Blossom End Rot is safe to handle and dispose of since a fungus or bacteria does not cause it. And you can eat tomatoes affected by Blossom End Rot, simply cut away the rotten end and eat the healthy part of the tomato.

While Blossom End Rot can be a frustrating problem for gardeners, it is not contagious and will not spread to other plants.

By understanding the causes of Blossom End Rot and implementing preventative measures, you can help prevent this condition’s development in your tomato plants.

Let’s find out what they are.

Incorrect Watering 

An incorrect watering schedule can cause Blossom End Rot in tomatoes due to its effect on calcium uptake. When tomato plants are not watered properly, the soil around the roots can become too dry or soggy. This can lead to a calcium deficiency, causing Blossom End Rot.

Tomato plants need to be well watered to avoid a calcium deficiency. Luckily incorrect watering is easy to prevent.

Depending on your climate and natural rainfall, tomato plants need 1-2 inches of water throughout the week. In summer, I water my tomatoes daily but when the weather starts to cool, I ease off the watering down to 2-3 times a week.

Tomatoes grown in pots will require additional watering as they tend to dry out faster.

As a general rule of thumb, water your tomato plants if the soil is dry about 1 inch below the surface. You can do this by checking with your finger, or you can use a soil monitor like this one which will check the moisture level for you.

Adding a 2-inch thick layer of mulch around your plants will help the soil remain damp. 

It is important to monitor the soil moisture level regularly to ensure that the plants are not being overwatered or underwatered.

Your watering schedule should be adjusted if you have rain during the week so you don’t overwater.

Poor Soil Conditions 

Tomato plants require specific soil conditions to thrive and produce healthy fruit. The soil conditions suited to tomato plants are: 

  1. Well-drained soil: Tomato plants require well-drained soil that is not waterlogged. Overly wet soil can lead to root rot and other diseases, damaging or killing the plant. If the root system is damaged, it can not carry the calcium to the tomato fruit. 
  2. Nutrient-rich soil: Tomato plants require soil rich in nutrients, especially nitrogen, phosphorus, and potassium. These nutrients are important for the growth and development of the plant and the production of healthy fruit.
  3. Proper pH balance: Tomato plants prefer slightly acidic soil with a pH between 6 and 6.8. Soil that is too acidic or too alkaline can lead to nutrient deficiencies. You can check your soil pH with this soil gauge here.
  4. Organic matter: Adding organic matter to the soil can improve its structure, fertility, and water-holding capacity. Organic matter can be added as compost, aged manure, or other organic materials.
  5. Warm soil: Tomato plants prefer warm soil, with a minimum temperature between 60-70 °F (16-21 °C) but the warmer the better. When the soil is still cold, planting tomatoes too early in the season can lead to Blossom End Rot. 

The soil must be properly prepared before planting tomatoes, ensuring optimal growing conditions and preventing Blossom End Rot. This may involve adding compost or other organic matter to the soil, testing the pH with a home testing kit, and amending the soil as needed. 

Planting your tomatoes in less-than-ideal conditions is ok, as soil conditions can be fixed. If your pH balance is off, you can add sulfur or de-acidifier to lower the pH levels or limestone to neutralize the acidity. Though in the case of lowering pH, which can be tricky to do successfully, my preferred method if possible is to use homemade compost along with aged manure to help feed to soil everything it needs before and throughout the growing season.


Over-fertilization of tomato plants can lead to an imbalance of nutrients in the soil, which can contribute to the development of Blossom End Rot.

Excessive nitrogen can interfere with the plant’s ability to absorb calcium, an essential nutrient for developing strong cell walls in the fruit. Without adequate calcium, the cell walls in the fruit can begin to rot at the bottom. 

In addition to nitrogen, over-fertilization with other nutrients, such as potassium and magnesium, can also contribute to the development of Blossom End Rot. These nutrients are important for healthy plant growth, but an excess can interfere with calcium uptake and other essential nutrients. 

To ensure your tomato plants receive the right nutrients, you need to check your fertilizer instructions. Some require an application every few weeks, while others only require 2-3 feeds during the growing season. It is also important to choose a balanced fertilizer like this one that contains the essential nutrients that tomato plants need, including nitrogen, phosphorus, and potassium.

The addition of compost and aged manure a few times during the growing season will also keep your tomato plants happy.

If you think you have over-fertilized your tomato plants, first, you need to remove any excess fertilizer. Next, you must flood the soil to wash away any excess fertilizer.

I have found flooding them in the early early morning worked best because the sun made sure to dry up the water quickly, minimizing the risk of leaving the soil waterlogged for an extended period of time. 

Environmental Stress 

Tomato Blossom End Rot - Tomato Growing Problems
Blossom End Rot on a still green Tomato

Another factor that can contribute to a calcium deficiency in tomato plants is environmental stress. This refers to anything within the tomato plant’s immediate environment that can influence it. Two factors that can lead to a calcium deficiency in tomato plants and therefore Blossom End Rot are extreme temperatures and overcrowded roots. 

Extreme Temperatures 

When tomato plants are exposed to high temperatures over 90 °F (32 °C) for a prolonged period during a heat wave, they will begin to droop. Extreme humidity will have a similar effect on tomato plants. 

When a tomato plant wilts due to a lack of water caused by heat, its calcium uptake will not be what it should be. The stress put on the tomato plant by too much heat or humidity causes the fruit to rot. To combat this, ensure you increase your watering schedule accordingly. 

Overcrowded Roots 

Another environmental stress factor that can cause Blossom End Rot is overcrowded roots. Overcrowded roots make it difficult for the tomato plant to absorb and transport calcium. 

When the roots of a tomato plant become overcrowded, they compete for nutrients and water, resulting in reduced calcium uptake by the plant. 

Now for the science behind it; calcium is transported to the developing fruit through the xylem, a series of tubes that run from the roots to the rest of the plant. When the roots are overcrowded, the xylem can become damaged or blocked, affecting calcium transport to the tomato fruit. As a result, the tomato may develop Blossom End Rot.

So ensure your tomato plants have enough space to grow and develop a healthy root system. Tomato plants should be planted 18-24 inches (45-60cm) apart, depending on the variety.

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