Blossom End Rot: How to Identify, Treat, and Prevent It

Blossom end rot is a common tomato problem associated with growing conditions. It affects tomato fruit. Stems and leaves show no symptoms.

What does blossom end rot (BER) look like?


The bottom side of the tomato (either a green or ripened one) develops a sunken, leathery dark brown or black spot. Gardeners most often notice BER when fruit is 1/3 to 1/2 its full size.

What causes it?

A calcium imbalance.

A tomato’s cells need calcium to grow. Calcium acts like glue in cells – it binds them together.

Tomatoes absorb calcium through water. But calcium isn’t fast-moving.

If a tomato grows quickly, or if other conditions slow water absorption, then calcium doesn’t have enough time to travel through the whole piece of fruit.

Plants can’t absorb enough calcium – whether or not there’s enough in the soil.

A tomato’s tissues break down and leave the telltale damage on its bottom.

Conditions that can slow water and/or calcium absorption can include:

  • inconsistent watering
  • root damage
  • cold temperatures/cold soil
  • excessive heat
  • too much nitrogen in soil (lowers calcium uptake)
  • large amount of salts in the soil (lowers the availability of calcium)
  • markedly acidic or alkaline soil (pH imbalance prevents calcium absorption)

When does blossom end rot affect plants?

Different conditions allow tomatoes to develop BER

  • when early to mid-season fruit develops, because soil is cooler and plants have fewer roots
  • during fruit set, and tomatoes need calcium to bind together cells
  • when watering is inconsistent
  • when temperatures are excessive – either too cold or too hot – which interferes with water uptake
  • when season starts out wet and turns dry during fruit set, just as tomatoes need calcium the most
  • when plants are grown in cold, heavy soil which prevents roots from developing strong
  • when soil has excessive salts, which reduce calcium availability

How can you control and treat blossom end rot?

Prevention is the most method of control (see below).

Blossom end rot cannot be reversed on a tomato once it’s set in, but you can take these steps to slow and halt it.

  1. Preserve affected plants by applying calcium immediately. You can use products specifically developed to treat, prevent, and slow blossom end rot in tomatoes like Tomato Rot-Stop Follow package directions for application. Or mix 1 tablespoon calcium chloride (sold commercially for other uses as de-icing salt or DampRid® Closet Freshener) in one gallon of water. Spray 2-3 times a week until blossom end rot is under control. Apply early in the morning when temperatures are cool. (Check out a good selection of garden sprayers here.)
  2. Pick affected fruit to reduce stress on the plant and allow it to direct its energy to other tomatoes. 
  3. Cut out spots on harvested fruit and eat remainder. Blossom end rot does not make the rest of the tomato inedible. However, if tomatoes have been infected by fungi or mold, discard them.

How can you prevent blossom end rot?

There are lots of ways you can take precautions for next year's crop!

  • Carefully harden off young seedlings gradually to protect them from extreme temperatures and conditions.
  • Select a planting area with good drainage.
  • Avoid setting out plants too early in the season, which can expose them to cold temperatures and cold soil. Allow soil to warm before planting.
  • Work in plenty of compost and organic matter into the soil before planting, so that the plant’s root system has a better chance to grow strong and deep.
  • Add quick-release lime when planting tomatoes so that there’s plenty of calcium in the soil and it’s absorbed quickly. Tomatoes grow best when the soil pH is about 6.5.
  • Keep your tomatoes’ water supply even throughout the season so that calcium uptake is regular. Tomatoes need 1-3 inches of water a week. They perform best when watered deeply a couple of times a week rather than superficially every day.
  • Mulch plants once established to maintain moisture levels.
  • Once blossoms emerge, apply tomato fertilizer that is high in phosphorus (the second number in a fertilizer’s three-number series), like 4-12-4 or 5-20-5. Too much nitrogen (the first number) or large amounts of fresh manure can prevent calcium uptake.
  • Cultivate carefully around tomato plants to avoid damaging root systems. Try not to dig more than an inch or two deep around plants.

Other facts about blossom end rot

Determinate tomato varieties are more prone to BER because they set fruit in a short period of time. Indeterminates and semi-determinates set fruit throughout the season, making it easier for plants to regulate calcium intake.

BER also affects eggplant, peppers, squash, and watermelon.

See more examples of Blossom End Rot on our Pinterest Board.

Tomato problems from growing conditions

Blossom drop – when tomatoes don’t set fruit ...

Why a tomato cracks and what to do about it ...

Sunscald: why too much sun can be hazardous to tomatoes ...

Are bumps on tomato stems harmful to plants?

How to identify tomato problems and prevent them ...

Tomato pests

The tomato hornworm: how to identify and control it ...

Tomato worms-cutworms: keep them away with stem collars ...

Stink bugs: how to identify and control them on tomato plants...

Tomato diseases

Different kinds of tomato blight and how to tell them apart ...

How to identify and treat Septoria leaf spot ...

More tomato problems

Problems on tomato leaves ...

Problems on tomato stems ...

Are There Problems on Bottoms of Your Tomatoes?

Is there a problem on the bottoms of your tomatoes? Explain what the problem looks like. Share what tomato variety you’re growing and when you first noticed the problem. While you’re at it, describe your growing conditions, the weather, and how much water your plants have had. Any details you can share will help us help you!

[ ? ]

Upload 1-4 Pictures or Graphics (optional)[ ? ]


Click here to upload more images (optional)

Author Information (optional)

To receive credit as the author, enter your information below.

(first or full name)

(e.g., City, State, Country)

Submit Your Contribution

 submission guidelines.

(You can preview and edit on the next page)

What Other Visitors Have Said

Click below to see contributions from other visitors to this page...

Why are all of my tomatoes are getting big rotten spots? 
Q. The majority of the tomatoes on my 16 tomato plants are getting these large rotten spots on them before they are ripe. Does anyone know what could …

Blossom End Rot on Tomatoes 
Q. Some of my tomatoes have a black spot on the blossom end (not stem end). Can you tell me the cause and cure for this problem? A. Blossom end …

The bottoms of my tomatoes look rotten 
Q. The bottoms of my tomatoes look rotten! What is this and what should I do? A. When the bottom side of the tomato (either a green or ripened one) …

Black bottoms on my tomatoes 
Q: How do I prevent black bottoms on my tomatoes? A : Tomatoes with black or brown leathery spots on the bottom side have succombed to blossom end …

Black soft bottoms on red tomatoes 
Dear Tomato Dirt, I have potted 2 tomato plants and they look great. They're growing well with green leaves and tons of tomatoes and flowers. However, …

The bottom of my tomatoes are turning brown before they get ripe Not rated yet
Q. I was so excited to pick the first tomatoes and was saddened to turn them over to find the bottom was rotten. The rest is good, but sure wastes a lot …

The bottoms of my tomatoes are turning black Not rated yet
Q. I only have 4 tomato plants. I planted them in mid May, I watered them every morning through our hot days and the first tomatoes were beautiful. Now …

Watering with water-softened water contributes to blossom end rot Not rated yet
I found that watering tomatoes using softened water (from a water softener) can contribute to blossom end rot. Softeners reduce calcium (among other agents). …

Tomato End Rot Not rated yet
Q. I am using cal-mag and chicken poop for my potted tomatoes and am still having problems with blossom end rot. I have tried everything from using products …

Tomato Blossom Rot Not rated yet
Q. I think my tomatoes have tomato blossom end rot. What causes it and how can I get rid of it? A. Blossom end rot is caused by a calcium imbalance. …

My tomatoes rot on bottom part Not rated yet
Q. My tomatoes plants are in pots, but once they begin to ripen, they start to rot on the bottom side. I have them on a sprinkler system to water 2 times …

Big black/brown areas on the bottom of unripened tomatoes. What are they? Not rated yet
Q.Our tomato plants are all at the early stages of the small green unripe tomatoes but on the bottom of the tomatoes that are maturing is a black/brown …

Click here to write your own.

Return from Blossom End Rot to Tomato Dirt home

New! Comments

Have your say about what you just read! Leave a comment in the box below.