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.

Microbe Science for Gardeners Book, by Robert Pavlis

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.

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. Robert , thanks for all your work. I have gardened for 50 years. I think at some point I have tried most all of the above. Without any scientific evidence to back up what I am saying I have noticed I get BER on the fruits that develop during a dry period followed by a wet spell. Mostly in the spring of the year when we get lots of rain and cool days. Once the weather settles and the hot days arrive BER tends to corrects itself.

  2. My tomato plant on the deck is grown in a large container of soil over a reservoir of water which is never allowed to run dry. The plant is a Celebrity and the fruit has BER. The roots are consistently watered.
    So, uneven watering must not be the culprit.

  3. Magnesium moves the calcium where it needs to go in the human body. As with plants. I add 1 tablespoon of magnesium to 1/2 cup of milk and mix that in my water in my watering pale. 2 to 3 days later my plants are producing twice as much an the blossom end rot is gone.

    • I find that hard to believe, because an increase in calcium will not “cure” BER once it has form. What you are the dead cells on the fruit, and they won’t come alive again.

  4. Perhaps the reason why people keep reccomending eson salts is that they work. Theory is nice but results are what matters. I often get blossom end rot and a solution of epson salts has always stopped it within a fewvdays.

    • How do you know it was the Epsom salts that solved the problem? BER tends to occur on the first fruits of the season, and then even with doing nothing, it goes away a lot of the time. The problem people keep recommending it is that they believe it works – but rarely have any evidence that it does. That is one of the main reason we have so many myths.

      • Robert,

        Here’s a published study that backs your assertion that adding Epsom salt (MgSO4) without good cause is not a good idea at least in tomatoes.

        Comparative Metabolomics Unravel the Effect of Magnesium Oversupply on Tomato Fruit Quality and Associated Plant Metabolism

        “5. Conclusions

        In conclusion, the untargeted metabolomic analysis of tomato revealed that Mg oversupply leads to altered root metabolomes, which can be attributed to the stress response of tomato plants to high magnesium levels. In terms of tomato plant metabolism, the present study demonstrated that differential concentrations of metabolites alter the commercially desirable traits of tomato fruits. This is particularly apparent in the root of the plant, which is the first organ to encounter Mg stress. We suggested that tomatoes allocate metabolite resources to roots through activating the metabolism of carbohydrates and polyamines. On the contrary, the metabolism of carbohydrates, amino acids, polyamines, phenylpropanoid was downregulated in leaves. In addition to these findings, Mg oversupply induced marked changes in the fruit metabolome. This was particularly apparent in the primary metabolites, which adversely affect its organoleptic properties and quality-determining traits. Thus, the present study concludes that the excess accumulation of Mg in the soil can have detrimental effects on the overall plant development and tomato fruit quality.”

  5. This study contradicts the theory that foliar application of calcium is fruitless (pun intended):

    The fact that calcium can’t flow from the leaves to the fruit does not prove that foliar spraying with calcium can’t cure or prevent blossom end rot. BER is a complex phenomenon- the biochemical mechanisms of which have yet to be fully elucidated. Perhaps when calcium is plentiful in the leaves, calcium from the soil is free to travel to the fruit instead. Perhaps there is alternative mechanism that has not yet been considered. Respectfully, I will await more evidence (and use calcium chloride), before deciding it is a waste of time to use calcium chloride foliar spray in the prevention and treatment of BER.

    • It may also depend on the type of plant itself. Peppers are not very good at calcium uptake. But in my case too little or too much water was the root (pun intended) of the cause. I feel the about my tomatoes but BER appears to go away after the first fruit.

  6. I once had big patches on my tomatoes, and everyone I spoke with (even the extension office) freaked out and thought it was blight or blossom end rot. I finally stumbled onto info that it was simply sunscald from pruning the plants. i wonder how many people make that mistake and buy products to try and fix it.

    • Interesting question. Sunscald is not uncommon and should be easily recognized by an extension office. But people like their chemicals when they have a problem.

  7. I wonder if it is due to the ammonia (in the form of chloramine, which also includes chlorine) that is now added to a lot of major city tap water systems. This could be the problem inhibiting how calcium is being used by the plant body. (I have to wonder what it is doing to the human body, too? Crippling and aging us, too!) There is also fluoride added to most city water systems, as well, another hormone inhibitor. Undoubtedly, in my opinion, and also in studies: all three of these chemicals working together (no less!) are screwing up lots of life-forms.

  8. The reason people recommend Epsom Salts is because magnesium is necessary in humans for the body to move calcium to the right places. I think that they are assuming the same holds true for plants.

    • That could be, but the people promoting Epsom salts are not thinking that much. They just believe anything on social media.

  9. Just came in from the garden where I found my Roma tomatoes have blossom end rot. Immediately pulled all I found. Noticed some of the blossoms on the bushes are turning black and not developing. Cut all I could find. Is this condition related to BER?

    • BER usually does not show up until the fruit is well on its way to develop. The black blossoms is probably something different.

    • Roma and other plum-shape varieties are more prone to BER for some reason. I’ve often had Romas in the same bed as other varieties. Same soil, same care, same weather. The Romas suffer BER, the others don’t.


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