Tomato Rot – How to Manage and Prevent Blossom End Rot

If you’re reading this, you are probably not in the best of moods. You’ve inspected your tomatoes and found them soft, squishy, and discolored at the base. You’re frustrated because you did everything right and followed all the guidelines, but here you are with tomatoes that won’t ever make it to a salad. Your fruit has tomato rot, also known as blossom end rot (BER), and you’ll need to dispose of all the affected tomatoes. However, don’t despair just yet! We have some valuable information to help you save the not-yet-affected tomatoes on your plants. We’ll also assist you in preventing and managing blossom end rot in your future tomato gardens.

This article will take you through what exactly is blossom end rot, how it occurs, and how you can arm yourself with gardening knowledge to help prevent it in the future.

We’re also going to help you try to save the rest of your tomato crop now.

Single green tomato with blossom end rot.
Table of Contents

    Understanding Tomato Rot (Blossom End Rot)

    If you ask enough people why blossom end rot occurs, you will have many single-note answers. 

    It could be not enough calcium or too much water – maybe not enough water – etc. But several factors can cause blossom end rot, and sometimes numerous circumstances can contribute to its onset.

    Ok, So what is Tomato Rot?

    Blossom End Rot, commonly known as Tomato Rot, is a physiological disorder that affects tomato plants. It shows up as a dark, sunken spot on the end of the tomato opposite the stem. At first, the affected area looks filled with water, but as time passes, it becomes brown or black and may become leathery or mushy.

    Semi red tomato with blossom end rot.  The tomato rot has turned black and has spread from the blossom spot to cover the entire end of the tomato.

    Causes of Tomato Rot:

    There are numerous causes of tomato rot, but it often always boils down to a lack of calcium. Either the soil has inadequate calcium, or there is a challenge the plant cannot overcome to adequately pull the calcium from the soil, either through watering issues, pH challenges, or environmental factors:

    Calcium Deficiency: 

    One of the primary causes of Blossom End Rot is a lack of calcium in the developing fruit. Calcium is essential for proper cell development and structural integrity. When the plant cannot transport enough calcium to the developing fruit, it leads to characteristic rotting symptoms.

    Inconsistent Watering: 

    Irregular watering practices can contribute to Tomato Rot. Fluctuations in soil moisture levels can disrupt the plant’s ability to absorb calcium effectively. Calcium uptake is hindered when the soil becomes too dry or wet, leading to fruit rot.

    pH Imbalance in the Soil: 

    The soil’s pH level plays a crucial role in plant nutrient availability. When the soil pH is too high or too low, it can affect calcium uptake. Acidic soils with low pH levels and alkaline soils with high pH levels can limit calcium availability, increasing the risk of Tomato Rot.

    Environmental Factors (temperature, humidity): 

    Environmental conditions can also contribute to Blossom End Rot. Extreme temperatures or exceptionally high heat, can disrupt the plant’s ability to regulate water uptake and transpiration, affecting calcium distribution to the fruits. High humidity levels can also exacerbate moisture-related issues, such as inconsistent water uptake and calcium transport.

    Varietal Susceptibility: 

    Certain tomato varieties are more prone to Blossom End Rot than others. Factors such as genetics and fruit characteristics can influence susceptibility. Therefore, selecting tomato varieties known for their resistance to Tomato Rot is helpful, especially if you have experienced the issue.

    Understanding these causes allows you to take appropriate steps to prevent and address Tomato Rot in your tomato plants. In the following sections, we will discuss treatments and preventative measures you can employ to ensure a healthy and robust tomato harvest.

    Still green, unripe, young tomato fruits affected by blossom end rot. This physiological disorder in tomato, caused by calcium deficiency.
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    Diagnosing Tomato Blossom End Rot

    To accurately diagnose Tomato Rot, it’s important to recognize its specific signs. Here’s what to look for:

    Dark, sunken areas: One of the main indications of Tomato Rot is the formation of sunken, dark spots on the blossom end of the fruit. At first, these areas might seem damp, but they will eventually turn black or brown. As the condition worsens, the affected tissue may become soft and mushy or tough and leathery.

    Localization at the blossom end: Tomato Rot is a type of disease that only affects the blossom end of the fruit, opposite the top stem. It begins as a small patch and can spread quickly, covering a large area of the tomato if not treated promptly. Unlike other fungal diseases, which can affect the whole fruit, Tomato Rot is more specific in its target.

    Progression of the Rot: Tomato Rot tends to develop gradually. You may notice a small, discolored spot on the fruit in its early stages. Over time, this spot enlarges and deepens in color, eventually affecting a significant portion of the blossom end. If left unchecked, the rot can lead to complete fruit decay.

    Tomato rot turning black on a still green tomato on the vine.

    Distinguishing Tomato Rot from other tomato diseases

    Distinguishing tomato blossom rot from other tomato diseases with similar visual characteristics is crucial for accurate identification. To accomplish this, consider the following tips:

    Fungal diseases: Unlike fungal infections such as early or late blight, Tomato Rot is localized at the blossom end and does not typically spread to other parts of the fruit. Additionally, fungal diseases may exhibit different symptoms, such as dark lesions with concentric rings, fuzzy mold growth, or visible spores.

    Bacterial diseases: Bacterial diseases like bacterial spots or bacterial cankers often present as dark lesions with irregular shapes, often surrounded by a yellow halo. They may also cause wilting or bumps on the plant stems or leaves. Unlike Tomato blossom Rot, these diseases typically affect various parts of the plant, not just the fruit.

    Viral diseases: Viral diseases, such as tomato mosaic virus or tomato yellow leaf curl virus, often result in distorted or mottled leaves, stunted growth, or yellowing of the plant. Unlike Tomato Rot, viral diseases do not cause specific localized symptoms on the fruit.

    By carefully your growing tomatoes, observing these symptoms, and comparing them to the characteristics of other tomato diseases, you can make a more accurate diagnosis of Tomato Rot. Once diagnosed, you can address the issue effectively with appropriate treatments and preventative measures.

    Treating Tomato Blossom End Rot

    There are several ways to help your crops if you consistently see blossom end rot:

    Correcting calcium deficiency:

    If you suspect Blossom End Rot in your tomato plants may be caused by a calcium deficiency, a soil test is recommended to confirm the root cause. This test provides valuable insights into nutrient deficiencies, particularly calcium levels in the soil. If the test detects low calcium levels, it supports the likelihood of calcium deficiency contributing to Blossom End Rot. 

    Fortunately, methods can address this issue and save your crop while preventing further damage. Correcting calcium deficiency is critical, and conducting a soil test first for tomatoes is a helpful step in identifying the problem.

    Soil amendment with calcium-rich materials (slower method):

    One of the most effective ways to replenish calcium levels in the soil is through soil amendment. Incorporate calcium-rich materials, such as gypsum or agricultural lime, into the soil before planting. These amendments gradually release calcium, ensuring a steady supply to your plants. With consistent application, you can help restore the balance of nutrients in the soil, improving calcium and nutrient uptake by the tomato plants.

    You can add things like egg shells to the soil, but it will take time for the calcium in the egg shells to become bioavailable; it will not help this year’s crops, but it will eventually break down and make the soil calcium rich.

    Cracked and cleaned brown egg shells on a bright white background.

    Foliar application of calcium-based sprays (quick method for this season) 

    To combat Blossom End Rot, one effective method is to directly apply calcium-based sprays to the leaves of your affected tomato plants. These sprays offer a quick and easily accessible source of calcium. 

    By regularly using them as directed, you can supplement calcium levels and alleviate the symptoms of Blossom and End Rot on your tomatoes. 

    Although it won’t reverse the damage caused to already affected fruits, it can help prevent future occurrences and support the growth of healthy fruits this season.

    Remember, treating Blossom End Rot requires patience and a proactive approach. Addressing the calcium deficiency that causes blossom end rot and providing the necessary nutrients can help your crop recover and enjoy a bountiful harvest. Stay positive and committed to preventing blossom end rot in your tomato plants, and you’ll be rewarded with vibrant, rot-free tomatoes you can savor and share.

    Foliar spray on a tomato plant.

    Regulating Watering Practices

    Proper watering techniques are essential for managing tomato blossom end rot. By adopting the following practices, you can help prevent and mitigate root damage and the impact of inconsistent watering:

    Consistent Soil Moisture

    Consistency is key when watering your tomato plants. Aim to provide regular, deep watering rather than frequent shallow watering. Keeping a consistent moisture level allows the roots to access moisture at a deeper level, promoting healthy plant growth and calcium uptake.

    Monitor the soil moisture by inserting your finger into the soil up to the second knuckle. If it feels dry, it’s time to water. By maintaining consistent moisture levels, you can help prevent the fluctuation that can contribute to Blossom End Rot.

    Tomato seedling with a stream of water from above.

    Mulching to retain moisture:

    Applying a layer of organic mulch around the base of your tomato plants can have significant benefits. Mulch acts as a protective barrier, helping to retain soil moisture by reducing evaporation. It also helps regulate soil temperature and prevents weed growth.

    Spread a 2 to 3-inch layer of straw, wood chips, and other types of organic mulch around the base of your plants, making sure to keep it a few inches away from the stem. This mulch layer will help maintain a more stable moisture environment for your plants, reducing stress and aiding in calcium absorption.

    Balancing Soil pH:

    Maintaining the proper pH level in your soil is crucial for preventing tomato blossom end rot. Here are some steps to help you balance the pH effectively:

    Testing soil pH: Use a soil testing kit or send a sample to a local agricultural extension office. A pH test will provide valuable information about the current pH level of your soil.

    Adjusting soil pH: If your soil pH is too slightly acidic (below 6.0), you can raise it by adding lime. Follow the recommended application rates based on your soil test results. For soils that are too alkaline (above 6.8), you can lower the pH by incorporating elemental sulfur or other acidifying agents. Again, follow the instructions and recommendations specific to your soil type.

    By achieving the optimal pH range for tomato plants (pH 6.0-6.8), you can enhance nutrient availability, including calcium, and create an environment that promotes healthy fruit development.

    Hand holding test tube with pH indicator comparing color to scale.

    Supplementing nutrients through fertilization:

    Proper fertilization is vital for your tomato plants’ overall health, lush growth, and nutrient balance. Consider the following steps to ensure they receive the necessary nutrients:

    Balanced fertilizer application: Choose a balanced fertilizer with equal or relatively balanced amounts of nitrogen (N), phosphorus (P), and potassium (K). Using a fertilizer with all the essential nutrients ensures that your plants receive all the necessary nutrients. Follow the package instructions for proper application rates and timing.

    Calcium-rich fertilizers: To specifically address calcium deficiency and prevent Blossom End Rot, you can also use calcium-rich fertilizers. Look for fertilizers with higher calcium levels, or add supplemental calcium sources, such as bone meal or crushed eggshells, to your regular fertilizer. This additional calcium will help support fruit development and reduce the risk of blossom end rot.

    Remember to follow the fertilization schedule and avoid over-fertilizing; using too much nitrogen as excess nutrients can lead to other problems. Regular and balanced fertilization will provide your plants with the necessary nutrients, including sufficient calcium alone, promoting healthy growth and reducing the occurrence of Tomato Blossom End Rot.

    Learn More: For more detailed information check out our full guide to fertilizing tomato plants!

    Pruning and Removing Affected Fruits:

    As part of your Tomato Blossom End Rot treatment plan, promptly identifying and removing affected tomatoes and fruits is important. Here’s how you can proceed:

    Pruning affected parts: Once you notice fruits displaying symptoms of Blossom End Rot, remove them from the plant. Use clean garden shears or pruning scissors to cut off the affected fruit, removing it entirely from the plant’s leaves first. 

    Still green, unripe, young tomato fruits affected by blossom end rot. This physiological disorder in tomato, caused by calcium deficiency.

    Preventing Tomato Blossom Rot

    There are many things a garden can do to help prevent losing crops of tomatoes to tomato rot. Here are a few easy things you can do to encourage a healthy harvest:

    Selecting Resistant Tomato Varieties:

    Choosing resistant tomato plant varieties is an effective strategy for preventing tomato rot. Look for varieties that are specifically bred for resistance to blossom end rot. These varieties are genetically equipped to handle calcium uptake and are less susceptible to the condition. When purchasing tomato seeds or transplants, check for labels or descriptions indicating resistance to Blossom End Rot.

    Blossom End Rot Resistant Tomatoes:

    • Celebrity
    • Fresh Pak
    • Jet Star
    • Mountain Pride
    • Pik Red
    • Cherry tomatoes
    • Heart-shaped tomatoes
    Beautifully full ripe red tomatoes on a vine, unblemished.

    Tomatoes Highly Susceptible to Blossom End Rot:

    • Roma-type tomatoes (San Marzano, I am looking directly at you!)
    • Beef Steak Tomatoes are moderately susceptible.

    Regular plant inspection and maintenance:

    Regularly inspecting your tomato plants and providing proper maintenance can help prevent and address issues before they escalate. Here’s what you can do:

    Visual inspection:

    1. Routinely examine your plants for signs of stress, disease, or insect infestations.
    2. Look for symptoms of blossom end rot, such as discolored or rotting fruits, and remove affected fruits promptly.
    3. Check for any abnormalities in foliage, including spots, wilting, or discoloration.

    Pruning and trellising: Prune excess foliage to improve air circulation and sunlight penetration. Pruning reduces humidity levels and minimizes the risk of disease. In addition, consider using trellises or stakes to support the plants and keep them off the ground, further reducing contact with soil-borne pathogens.

    Weed control: Regularly remove weeds from the vicinity of your tomato plants. Weeds compete for nutrients and water, creating an unfavorable growing environment. Additionally, weeds can harbor pests and diseases that may affect your tomatoes.

    Crop rotation

    Implementing crop rotation and effective pest control practices are crucial to preventing blossom rot. Consider the following measures:

    Crop rotation: Avoid planting tomatoes in the same location year after year. Rotate your crops by growing tomatoes in a different garden area every season. Crop rotation helps disrupt disease cycles and reduces the same nutrient depletion year after year.

    Tomato with rot developing on the bottom.

    Avoid Blossom End Rot With Good Garden Management

    We’ve all been there. Last year, I lost my first flush of San Marzanos to BER. I did all the things! But we had a very dry spring. It was a new garden (new zone, new everything), we had all kinds of challenges, and my watering plan was not up to snuff. When we noticed BER on our first fruit flush, I just about lost it (no, I did, I lost it, full transparency). We pulled all the rotten fruit from the plants, amended with more compost, started a weekly foliar spray with calcium, and laid down drip lines in all our tomato beds. Our second fruit flush had no BER.

    If you catch BER early enough in your season and are dealing with indeterminate tomatoes, you may fix the problem, and subsequent tomato flushes may be fine. So don’t lose hope.

    If you have any questions we didn’t answer, feel free to leave a comment below or reach out to us via email.

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