How To Prevent Tomato Rot

Tomatoes are among the most popular fruits that both novice gardeners and longtime vegetable farmers grow annually. And it’s no wonder why! They’re a delicious addition to salads, sandwiches, salsas, and ceviche, or just to be enjoyed on their own at the end of a long summer’s day.

But what happens when your beloved tomatoes begin to rot? It’s time to learn how to prevent tomato rot once and for all. We’re here to break down tomato blossom end rot so you can spend more time worrying about the perfect tomato recipe to serve for dinner.

What is Tomato Blossom End Rot?

Tomato rot—also known as tomato blossom end rot—occurs when the blossom end of the fruit (opposite the stem) breaks down and rots. The breakdown happens quickly. At first, it looks like water-soaked spots on the end of the tomato. Then, the area shrinks and becomes leathery as the tomato tissue breaks down and turns black.

Tomato blossom end rot will cause the entire tomato to look like it’s decaying. While it can happen at any time during the growing season, it most often occurs with the first tomatoes of the harvest—meaning there are actions you can take quickly to prevent your entire season’s crops from being ruined. 

What Causes Tomato Rot?

Believe it or not, the cause of tomato rot isn’t disease or pest infestation. Tomato rot is caused when a tomato plant can’t access calcium through its roots—not because of a lack of soil nutrition but because of inconsistent moisture during the growing season.

Tomato blossom end rot also occurs when young plants experience rapid growth. The plant’s growth spurt requires more calcium than it can uptake, which leads to rotting problems. Applying the right combination of an organic fertilizer in the right amount will help solve this problem.

7 Best Ways to Prevent Tomato Blossom End Rot

Since tomato blossom end rot is most likely to occur with your first harvest, there are ways to prevent it so you can salvage your later tomatoes. Better yet, apply these principles early, and don’t worry about tomato rot at all during your gardening season! 

• Know your soil
• Monitor calcium levels
• Apply water consistently
• Maintain pH levels
• Add a layer of mulch
• Avoid excessive digging
• Proper application of organic fertilizer

1. Know Your Soil

Your soil holds the key to your planting success. It’s important to perform a complete soil test early on to determine your needs. (The great news is that Rocky Mountain BioAg® also offers a soil test interpretation to ensure you accurately understand the results.)  

Using our soil sample equipment to learn more about your specific soil needs ensures a healthy, thriving tomato plant. Based on the results of your soil test, you may need to add materials, like organic fertilizer or mineral soil amendments, to help your tomatoes flourish. 

2. Maintain Calcium Levels

Calcium deficiency is the number-one cause of tomato blossom end rot. Your soil test may determine that you need more calcium in your soil. The best ways to increase calcium levels in your garden bed are by adding: 

• Diamond K Premium 97 Solution Grade Gypsum: If your soil has been waterlogged, utilize an organic fertilizer that incorporates gypsum. Gypsum, a form of calcium sulfate, helps improve soil structure and drainage issues, leading to better fruit quality.
• ProCal 3-0-0 Plus 20% Calcium Organic Fertilizer: If you’re looking for a robust organic fertilizer to help grow healthy plants, look no further. This fully soluble fertilizer allows the plant to easily move calcium to the tomato fruit. Because of the higher nitrogen count in this organic fertilizer, this is a better option for tomatoes early in the growing season.
• Crab Shell Flour: Crab Shell Flour is a fantastic dry plant food that provides essential nutrients, including the calcium your garden is lacking. 

3. Apply Water Consistently

One of the best ways to prevent tomato rot is by maintaining consistent moisture levels in the soil. Don’t overwater or underwater—this is a Goldilocks situation, and your water levels must be just right.

Tomatoes need about an inch of water every week from rain or irrigation. Watering consistently ensures the calcium in the soil can be taken up by the roots. If overwatering happens, the calcium deficiency occurs because it flushes out of the fruit more quickly.

4. Maintain pH Levels

You know there’s going to be a secret weapon for an uber-successful tomato plant, right? And here it is: Your soil’s pH levels are the secret to your tomato plant’s success. 

Maintaining the correct soil pH level is crucial for preventing tomato rot. Ideally, plants thrive in a slightly acidic (6) to neutral (7) pH range. Test the pH of your soil and add materials, like Dolomite Lime, as and if needed, to bring your soil’s pH into the appropriate range for healthy tomatoes. 

5. Add Mulch Around Your Plants

Apply a 2-inch layer of mulch around the base of your tomato plants to maintain consistent moisture levels and stave off tomato blossom end rot. Mulch will keep the soil moist without waterlogging it. Even better, it helps the plant maintain a stable temperature and keeps those pesky weeds away.

6. Avoid Excessive Digging

The plant’s root system is vital to ensure the tomato gets enough calcium and water to prevent tomato blossom end rot. Avoid digging too much around the root system, especially when the fruit is forming, to maintain a healthy uptake of nutrients—mainly calcium. 

7. Proper Application of Organic Fertilizer

An important component: You must know how to use organic fertilizer for plants for the best results. Using too much organic fertilizer causes the plants to grow faster than the calcium they need can travel for healthy growth, which ultimately causes tomato rot.

Before you ever plant in the spring, adding a 2-inch-thick layer of well-decomposed compost will help boost your soil’s nutrients. Only apply organic fertilizer if it is recommended by the results of your soil test, and when doing so, follow the label instructions carefully.

Can Tomato Rot Spread to Other Plants?

The great news about tomato rot is that it isn’t contagious. It won’t spread from your afflicted tomatoes to other plants in your garden. However, if conditions are right (and especially if your plants have been overwatered), nearby plants may be infected with the same type of fungus and have similar symptoms. To minimize the risk of spreading tomato blossom end rot, properly dispose of affected fruits or vegetables immediately after you harvest them from your garden beds.

While tomato blossom end rot is serious, it’s also curable. Vegetable gardens are a labor of love and require a lot of time throughout the growing season. Tomato rot happens to even the best in the industry, and through proper precautions, you’ll have the garden (and dinner table) of envy every summer.