Blossom End Rot

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Robert Pavlis

Blossom End Rot (BER) is a disfiguration found in fruiting vegetables, like tomatoes, peppers, watermelons, egg plants and apples. This problem is usually blamed on a shortage of calcium, but this turns out to be a myth.

blossom end rot in tomatoes
Blossom end rot in tomatoes, photo source:  NC State University

Blossom End Rot – What is it?

Blossom End Rot or BER shows up as a small wet water-soaked spot at the blossom end of the fruit. Over time it darkens to a brown or black color and becomes leathery and hard. This is not a disease, as reported by many web sites, nor is it the result of insect damage. As the fruit grows, something goes wrong with the normal growth process and the cells in the fruit start to die. The dead cells turn black and hard. It is a physiological condition due to the plants environment.

BER is most common on the first fruits of the season, but it can occur at any time.

The fruit, once affected, will not develop properly, and can be discarded so the plant can focus it’s energy on newer fruit.

Blossom End Rot – What Causes it?

For years it was claimed that a lack of calcium was causing Blossom End Rot since fruit with BER has low calcium levels.

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For some time scientists thought that the problem is one of moving calcium around inside the plant, not necessarily a shortage. Various ‘transporter’ compounds, such as gibberellins and a recently isolated protein are responsible for moving calcium to points in the plant where it is needed. Calcium is required for cell growth and so it is required in fairly large amounts by the developing fruit. When these transporter compounds are not doing their job properly, it results in low levels of calcium at specific points in the plant.

The latest research shows that BER develops in the fruit first and only after it is a problem, do calcium levels in the fruit change. What this means is that:

BER causes a calcium deficiency in the fruit – not the other way around.

Once you understand the real problem, it becomes obvious why many of the remedies for BER don’t work.

What Causes Blossom End Rot?

The most common cause is irregular watering but other environmental factors can also cause BER, including salinity, drought, high light intensity, heat, and ammonia nutrition.

For example, cool temperatures affect the level of gibberellins, which in turn may lead to BER. This may in part explain why BER is more common early in the season when it is cool.

How do You Solve Blossom End Rot?

In many cases the plant seems to grow out of the problem over time. As mentioned above, the first fruit of the season is most likely to have the problem, and after that, fruit grows normally–for no clear reason.

The following are some solutions that have been proposed:

1) Fertilize with calcium. It is possible that the soil is deficient of calcium, and if this is the case fertilizing with calcium will may help eliminate BER. However, most soil has lots of calcium and if it does have calcium, fertilizing with more will not help the problem. Too much fertilizer may exacerbate the problem by making it harder for the plant to absorb calcium. For example, excess ammonium can make it harder for the plant to absorb calcium.

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2) Spray calcium fertilizer on the leaves i.e. foliar feed. Foliar feeding is not a good long term solution for feeding plants especially for home gardeners, at best it is a quick fix solution. Calcium only moves in the plant via the xylem from the roots, up the plant and into growing points. Calcium has no ability to flow from the leaves via the phloem to the developing fruit. 

An interesting experiment measured the effects of calcium foliar spray on tomato plants and found that it affected both plant growth and reduced BER. It is possible that the increase of calcium in the leaves results in more calcium being directed to the fruit from the roots. This is just one study, but calcium foliar spray may reduce BER.

3) Spray calcium on the fruit. Fruit has a tough waxy outer skin that is not very permeable, and it has no stomata to allow nutrients to enter. It is even less likely to absorb calcium than the leaves. This does not work.

4) Treat the plant with Epsom salts. I don’t know why people keep recommending Epsom salts to solve problems–it’s just silly. Epsom salts is magnesium sulfate–it does not contain calcium! Blossom End Rot has nothing to do with a magnesium shortage.

5) Water more, or less. There is some evidence that water levels in the plant play a role in calcium levels in various parts of the plant, and water levels may have an effect on the transporter compounds. The problem with this advice is that it is difficult to know if you need to increase or decrease water levels. Keep the soil moist and don’t over water.

6) Grow a different variety of tomato. This can work. Some varieties are more likely to get Blossom End Rot so growing a different variety could solve the problem for you.

7) Adding bonemeal or lime to the soil. Both these products contain calcium and if your soil is deficient of calcium, these might help. Keep in mind most soils are not deficient of calcium, so I would not use these products until you have a soil test done.

8) Don’t over fertilize with nitrogen. This is important and can contribute to BER. Too much nitrogen causes the plant to grow more leaves. As water is drawn towards the leaves, it carries calcium with it which may in turn reduce the amount of calcium going to the fruit. Over fertilization also increases the amount of salts around the roots, which makes it harder for the plant to absorb calcium.

There is no magic bullet to solve Blossom End Rot. Treat plants the way they want to be treated (good soil, compost, regular water etc) and you should not have serious problem. But if you do have BER, don’t believe everything you read.

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

60 thoughts on “Blossom End Rot”

  1. And then there’s the fact that some varieties are more prone to BER. Eg, the plums. I’ve had countless cases of different varieties in the same beds, same soil, same watering, same weather, and BER affecting the plums but none of the others. Always had to assume it’s something genetic.

  2. I’ve had issues in the past with BER. About 15 years ago I stopped tilling. Went to a deep mulch, layering method. Only using a broad fork to work the soil. I’ve been using leaves from the yard chopped up, green cut sawmill dust and compost as mulch. I also began using fungi mycelium in the form of shiitake and king oyster mushrooms to break down the woody materials. I’ve not seen BER in 10 years. I don’t water at all, we live in Oklahoma zone 7b. Only water the gardens get is rain.
    I’m not botanist or biologist, just permaculture gardener. I do believe there is direct relationship to photosynthetic plants fungi and bacteria that tilling disrupts. Might be an area to further research in future thanks for taking time to read this.

      • Could be that the mulch prevents the soil from drying out as much though. Maybe fungi mycelium can also transport water from elsewhere in the soil to the vegetable plant’s roots?

      • I haven’t had blossom end rot issues with in-ground tomatoes, but did have a problem with container tomatoes, until I added a couple inches of pine needle mulch to the top of the containers, and then the problem went away, and the soil remained moist even if it only received water 1-2 times per week.

  3. Nice article. I have found that my tomatoes and peppers get BER from un even watering. Originally I added calcium but of course that did absolutely nothing. Epsom salts will not help as well but I have had it turn my basil plants from pale to vivid dark green. I also apply it to my peppers and had good results. There may be no science backing this up but it works. There are just a few things like spaying my as tomatoes with aspirin to fend of disease works and again no science. As for BER I put everything on soaker hoses with a timer and topped the garden with mulch… more BER!


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