Prevent Blossom End Rot: Tips for Healthy Tomatoes

By: Angela Judd | June 3, 2024

The tomato looks perfect, and then you turn it over and see the telltale dark, leathery spot on the bottom. This frustrating condition is known as blossom end rot, and it can affect a variety of fruits and vegetables. Learning to identify, treat, and prevent blossom end rot will help you avoid this common problem.

Article Outline:

What does blossom end rot look like?
What is blossom end rot?
Does this mean my plants need more calcium?
What are the common causes of blossom end rot?
Can you fix blossom end rot?
How to avoid blossom end rot

What does blossom end rot look like?

The easiest way to identify blossom end rot is to look for a dark, sunken, or decayed spot on the bottom of the fruit. But, the first sign of blossom end rot is usually a small water-soaked spot at the blossom end of the fruit. As the condition progresses, it will grow, eventually turning brown or black and sunken. The inside of the fruit also decays.

Some fruits may have leathery spots on the top of the fruit. This is usually sunscald or sun damage, not blossom end rot.

Sunscald on peppers and tomatoes - not blossom end rot — Sunscald on peppers and tomatoes – not blossom end rot

Summer squash may not develop properly. Withering fruit is usually caused by poor pollination, but summer squash can also develop blossom end rot.

Poor pollination on squash plants — Poor pollination resulting in withered summer squash

What is blossom end rot?

Blossom end rot is a common disorder that affects tomatoes, peppers, squash, and other fruits and vegetables. It occurs due to a calcium deficiency in the tomato’s tissue, which leads to poor cell wall development and dark spots on the fruit.

The plant absorbs calcium through its roots, but it tends to accumulate in certain parts of the plant. As a result, the rot can develop even if there is plenty of calcium present. Developing tomatoes require a consistent supply of calcium for healthy fruit development.

Does this mean my plants need more calcium?

The answer is yes, but you may not need to add it. The soil often contains plenty of calcium, but the plant can’t access it.

What are the common causes of blossom end rot?

Inconsistent watering: Fluctuating soil moisture levels disrupt the plant’s ability to absorb calcium effectively. Hot, dry weather can cause water stress, reducing the plant’s ability to take up calcium. Too much water (or rain) may wash the available calcium from the root zone.
Young plants: Blossom end rot is common on the season’s first fruits. When plants are young, and their root systems are still developing, they may struggle to absorb sufficient calcium from the soil.
Too much nitrogen: The rapid growth caused by overfertilization may direct available water and nutrients to the leaves and starve the fruit.
Damage to the roots: Cultivating too close to the roots or fertilizer burn can prevent calcium uptake.

Can you fix blossom end rot?

While it’s true that blossom end rot on individual fruits can’t be “undone,” There is hope. Once you notice blossom end rot on the fruit, remove and discard the fruit. The rot will not spread to other fruits. Do not use fungicides or pesticides; they will have no effect.

Do your best to identify the likely cause of the problem. If possible, take steps to remedy the situation. Employing the prevention strategies listed below can significantly reduce the chances of subsequent fruit suffering the same fate.

How to avoid blossom end rot

Maintain even moisture. Moisture stress is the most common cause of blossom end rot. To keep the soil evenly hydrated, consider using drip irrigation, which delivers water directly to the plant’s roots, and apply a thick layer of organic mulch, such as straw or wood chips, to help regulate moisture and prevent evaporation.
Avoid digging around plants’ roots. Root damage limits the plant’s water uptake ability, especially when it’s hot and dry.
Maintain proper pH and nutrient levels. A soil pH of 6.5-6.8 is ideal for tomatoes. Adequate levels of calcium, phosphorus, and nitrogen are also necessary. Testing and amending before planting helps ensure healthy tomatoes. Here’s the soil test kit I use on Amazon.
Ensure good drainage. Well-draining soil prevents salt-build up that can prevent nutrient uptake.
Choose resistant varieties. Some tomatoes, like Celebrity and Mountain Pride, are less vulnerable to this condition. When selecting tomato varieties, look for those labeled ‘blossom end rot resistant’ or ‘BER resistant. ‘ These varieties have been bred to be less susceptible to blossom end rot.

As a gardener, your role in identifying, treating, and preventing blossom end rot is crucial. By being vigilant for early signs of this disorder and making necessary changes, you can prevent blossom end rot from ruining your harvests. Your actions can make a significant difference in maintaining the health of your plants.