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”

    • There is a shortage of drinking water in some places, but most certainly not in others. I’ve lived in both types of places. Take out the ‘globally’ and the statement becomes correct.

  1. I like how Robert points out the finer distinctions at the core of science that get lost when it goes into the mainstream and gets consumed by nonscientists (e.g., between lack of nutrients and lack of nutrients where they are needed) and how he addresses rational comments with rational answers, corrects himself when he kind of says something not precisely right… and does so in a respectful, approachable way. Science is never really clear, and bringing it down from the ivory tower to the garden is even more of a challenge. Thank you Robert!

  2. “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.”

    Because Calcium, Magnesium, and Potassium are all interrelated and they each affect each other. Adding any of the three causes changes in the cation availability of the other two.

    Magnesium regulates metabolism. Where there’s not enough of it in the plant tissue, it affects other biological processes, such as the assimilation and mobility of calcium.

    Nothing happens in isolation inside a plant.

    • No. From University of Minnesota : “The causes of catfacing are not definitely known, but it is generally agreed that any disturbance to flowers or flower buds can lead to abnormally shaped fruits. Cold temperatures and contact with hormone-type herbicide sprays are commonly believed to be responsible for catface.”

  3. We have been taught recently that BER is not a lack of Ca, but instead variations in water levels making the Ca unavailable to the plant/fruit. You hit the nail on the head several times here-make sure that there is enough Ca in the soil; water consistently (don’t let them dry out and then drown them); and this is super important I think….change varieties. We grew hybrids (Celebrity, Polbig, Defiant) right along with some heirlooms (Rose, Gilbertie) one year. Almost all of the Rose tomatoes had BER, lots of the Gilbertie had it, but NONE of the hybrids!

    • BER is a lack of calcium, but a lack in the fruit, not the soil.

      I am not surprised that different varieties of tomato have different tendencies towards BER. And plant breeding usually selects for varieties that do better. Heirloom is not always better.

    • I should have made my first statement a little clearer-not necessarily a lack of Ca in the soil, but as you said, a problem getting that Ca to the plant parts. We were told that consistent watering can aid in this problem. I don’t know that it’s true, but it works for us! We use drip irrigation in our high tunnel and add a chelated Ca product once or twice a week alternating with small amounts of water soluble fertilizer-it makes me feel better! I guess I’ve never seen great results from foliar applications of anything! My neighbor seems to have problems with BER each year….he does seem to apply copious amounts of fertilizer….wondering if that is his problem???

      • Water fluctuations do seem to make BER worse.

        Lots of fertilizer could be causing all kinds of problems. It could be raising pH in which case calcium becomes less available. The salts in fertilizer will also react with each other and it could be precipitating the calcium out of solution. Soil chemistry is much more complicated than people realize and science still has lots to learn about it. It is clear that adding fertilizer in excess can cause all kinds of problems.

        • During my childhood my uncle would visit us every spring to plant our 1/2 acre vegetable garden. He would first come about a month before planting seeds, to take composted mulch and turn it into the soil. We never used any commercial fertilizer other than some manure every few years, never any poisons for pest. Never weeded just turned them into the soil between rows. And every year was a victory garden. Sure some of the leaves on the chard had a few holes from pincher bugs but never made a difference in the kitchen. Nature does pretty good if also have an uncle with a thumb greener than grass.

  4. Um. I’m sticking my neck out again.

    I garden on acid sand and have a persistent problem with BER on courgette, plus occasionally on tomatoes (but no bitter pit on apples). The soil is limed occasionally, and the crops rotated fairly strictly, but both the weather and I are erratic and irregular waterers. And I dig in a lot of animal muck, but rarely feed plants otherwise.

    This year, I tried a new method of watering/feeding the tomatoes, using a two litre pop bottle, screwed into a pierced spike, thrust into the ground (through the three inches of spoiled haylage mulch) by each plant (17 tomatoes and 6 assorted courgette). My original intention was to avoid wetting the leaves in my on-going battle against late blight, but I found it an excellent method of feeding, I actually knew that it was delivered to the root system and not just running off the surface down the garden path. So I did feed the toms, once a week, as per the bottle of Tomorite.

    When baby courgette started rotting at the end, and one or two tomatoes showed BER, I dosed with calcium nitrate once a week – 2 heaped tablespoons per five litre watering can per three plants.

    No more BER. Healthy baby courgette within 24 hours.

    I continued for three weeks and then ran out of calcium nitrate.

    Going on gut feeling, anecdotal evidence, and intuition….it did seem to work for me. Rather wish you hadn’t scientifically demolished it quite so thoroughly!

    • Courgette? Never heard Zucchini called that before. 🙂

      I never said calcium can’t cure BER. If you have a calcium deficiency in the soil, calcium will help. It is just that most people don’t have this deficiency in home gardens. Sandy soils are known for their nutrient deficiency. Sand does not hold onto nutrients of most types as strongly as clay or humsy soils.

      BER also seems to correct itself. It is quite common to see it on the first few fruits and then it goes away on it’s own.

    • So delighted to find Mr Palvis article on BER. I am in the mountains about 800 ft above sea level in Lebanon
      Second year of BER. Small Hybrid veggies from US fine, soil is good , maybe watering style not consistent, by hand
      BTW Courgette are French pale green squash. Common in the Middle East .
      Thank you. Great website!

    • Hi Deborah, I thought I had blossom end rot on my courgettes/zucchinis, only to discover that it was actually a lack of pollination. The ends of the fruit don’t develop and then they rot, even if the base of the fruit swells. I found hand pollination in the morning really helps, and growing them adjacent to herbs like basil, sage and rosemary in flower which attract pollinators. It is always a problem for me with the first couple of fruit on the plant, as often there are simply no male flowers developed yet on the plant for pollination to take place. I realise that you commented five years ago, but thought it might help someone else too!

  5. Re: Epsom salts. I don’t know about plant cells specifically, but I do know that in human cells, magnesium is the transport mechanism for moving calcium in and out of cells, much in the same way that sodium and potassium are two halves of the transport mechanism for moving water in and out of cells. Epsom salts are magnesium sulfate. Potentially then it should be able to assist in calcium metabolism to the fruit.

    • Magnesium does not seem to be involved in plants. Reference 2 talks about gibberellins and abscisic acid controlling calcium levels in the fruit.

      • My understanding is that magnesium is directly related to photosynthesis but high levels can directly affect absorption of calcium by the roots.

  6. BER is caused by inconsistent watering, simple. Had the problem a couple of times, both stopped when automatic watering systems were installed. Convinced based on this that BER s caused by variations in soil moisture, beyond that which the plant can tolerate.

    • Your conclusion is mostly correct, but it is not ‘simple’. In fact scientists have been studying the problem for many years and there are still some things about BER they don’t understand. Plant systems are very complex.

  7. Hello and thank you for your website and many articles. My question is with your statement: “…. First of all foliar feeding is not a very good way to get nutrients into a plant–it is just not very effective. …”

    How does this reconcile with studies conducted by Dr. H.B. Tukey et al, that showed when they compared the nutrient uptake at the roots from a soil application versus foliar spraying and found that a 95 percent efficiency of uptake compared to about a 10 percent efficiency from soil applications?

    Thank you again for your valued writings.

    • Dr. Tukey did show that nutrients were absorbed by the foliage of the plant. It is certainly accepted today that spraying some chemicals onto leaves results in the plant absorbing the chemical. For example, if a plant is showing an iron deficiency, you can spray with an iron compound and see fairly quick improvements in chlorosis.

      Are the numbers 95% and 10% correct? They are certainly quoted by many people. I have not looked at the original research paper, but this one seems like a good summary. It is written by Dr. Tukey, but not dated. His conclusion is “If we apply these materials to the leaves in soluble forms, as much as 95% of what is applied may be used by the plant. If we apply a similar amount to the soil, we find that only about 10% of it is used.” A key word is “as much as”.

      In his experiment he used phosphorus and compared foliar feeding to several types of soils. Some soils are more efficient, and some nutrients are absorbed more slowly by leaves. At best the 10 to 95 ratio is an approximation. However, foliar feeding was significantly more efficient.

      The experiment was conducted for 3 weeks. Foliar feeding is going to be a rapidly process. After 3 weeks you are not going to get more absorbed. In realistic conditions rain is likely to shorten this period, since rain would wash off any material not yet absorbed. When phosphorus is added to soil, it moves very slowly in the soil. Adding phosphorus on the top layer of soil results in it moving down the soil at a rate of a couple of cm per year. But eventually it gets to the roots–but not in 3 weeks.

      The plants in the experiment were tested 3 weeks after phosphorous was applied. But in the real world, the phosphorus that is not used in 3 weeks will be available for use in the future. Dr Tukey did not take this into account when he made his conclusions. Feeding through the soil is a long term process.

      I think it is more correct to say that foliar feeding is a quick way to get some chemicals into the leaf. Based on his experiment one can not conclude that in the long term foliar feeding is more efficient than feeding through the soil.

      What about BER? Dr. Tukey says “Calcium, strontium, barium, iron, and magnesium were readily absorbed but did not move out of the leaf to which they were applied.” And this is what I found others saying as well. The plant does not have a good mechanism for moving the calcium from the leaf to the fruit. To simplify things we can think of it as a one way road from roots to fruit. There is no connecting road from leaf to fruit. At best the calcium would need to travel from leaf to root, and then back to fruit, and that does not seem to happen to any significant extent. For this reason foliar feeding with calcium is not effective against BER.

      What about my statement “First of all foliar feeding is not a very good way to get nutrients into a plant–it is just not very effective”. I have to agree that this statement is not entirely correct as written. What I should have said is that “First of all, foliar feeding is not a good long term solution for feeding plants, at best it is a quick fix solution” . I have changed the post to reflect this.

      Thanks for pointing out the mistake.

      • Where I live here in the south, in general, getting leaves wet is a a bad idea period. Unless you like fungal problems. The air is wet enough.


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