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I find myself having to take notes in order to keep the information straight when I read scientific papers, so when I dug out the following review paper on the topic I decided to summarize the relevant information and add some comments to tie the science talk to backyard gardening conditions and practices. The paper itself focuses on the cellular/physiological aspects of BER, which does not concern us gardeners, but it also contains quite a bit of background info that does concern us. However, most of that background is from BER problems in commercial greenhouses, conditions and practices very different from outdoor gardens exposed to the whims of Mother Nature, so their conclusions as to what works and doesn't work must be considered in that context.

I do suggest looking at the article as some of the figures are informative.

https://aob.oxfordjournals.org/cgi/reprint/95/4/571

https://aob.oxfordjournals.org/cgi/content/full/95/4/571

The article:
A Cellular Hypothesis for the Induction of Blossom-End Rot in Tomato Fruit
LIM C. HO and PHILIP J. WHITE*
Annals of Botany 2005 95(4):571-581

My synopsis for gardeners

BER is caused by multiple cellular problems in the distal end of fruits, which result from low available calcium at that location during the first two weeks of fruit development (just after the flower fades and falls away, when most of cell division and differentiation is taking place). Because of the low number and structure of transport vessels in their fruit plum-shaped tomatoes are more susceptible than round fruited varieties. BER calcium sprays [calcium chloride et al.] applied before the second week of fruit growth can help directly, sprays are the best way to control BER under the controlled conditions of a greenhouse [But other steps might be just as effective in the more variable conditions of an outdoor garden--TZ].

Calcium can either be restricted from entering the plant (soil-root conditions) or be inefficiently transported to the distal part of the fruit once in the plant. The latter is caused by above ground conditions affecting leaf water loss and photosynthetic rates.

BER can be induced by a number of growing conditions, such as low soil calcium, low phosphorus, high magnesium, high nitrogen (particularly NH4), high potassium, high salinity, drought, water logging in the root zone, cold soil/roots, and also low humidity, high light, high temperature and high air movement in the leaf-shoot environment. When soil calcium is plentiful roots may not be able to take it in efficiently when the soil is cold or waterlogged. Once calcium is in the plant it is dependent on high turgor pressure to get to the distal part of the fruit. If water loss/transpiration is high from the leaves turgor pressure is reduced in the plant. At its most critical low pressure the plant wilts because it can't get enough water to its leaves. Bright light, heat, low humidity and air movement contribute to high water loss.

Movement of water up from the roots is mainly driven by negative pressure formed by evaporation within the leaves, so the leaves are literally sucking water from everything below them including the fruits. Root pressure is a much weaker force and pushes water up into the plant. It is driven by the difference in dissolved substances between the internal water and the soil water. As soil dries the concentration of dissolved substances in the remaining soil water increases, thus reducing root pressure in the plant, high salinity in moist soil has the same effect.

In addition to water transport effects, bright light also boosts photosynthesis and thus fruit growth. This is bad if the rate of calcium entering the fruit is not adequate to support the increase in growth rate.


Here is my interpretation of that information as it regards garden growing.


Some scenarios for BER

1) Cold wet cloudy conditions suddenly change to warm and sunny conditions soon after fruit set. The plant ramps up fruit growth while cold oxygen starved roots can't take in calcium fast enough.

2) The garden is shallowly tilled/amended over more compact subsoil layer, and the soil is high in nutrients from pre planting fertilizer application. Shallow rooted plants grow big, and then hot weather hits on schedule in early summer just as lots of tiny fruits are forming. The big leafy plants suck all the water out of the top layer of soil, reducing their internal water pressure and starving the fruits of calcium.

3) You are growing in low calcium, high fertilizer conditions with fluctuating water availability. This often resembles a five gallon bucket of potting mix, or low quality hard dirt with little organic matter, or a sand box.

4) You are growing Roma/plum tomatoes under ALMOST perfect conditions.


If you are plagued by BER, what can you do other than spray the plants with an anti-BER calcium solution when the fruits are barely visible (0-2 weeks old)?

Because soil calcium is rarely critically low, and because you cannot control cloudy, rainy, sunny, hot, dry or windy weather here are some things that you can try without having to test your soil for pH-calcium levels.

1) Soil: Make sure your soil both drains well and is water retentive. This means deeply dug with a lot of organic matter so that it provides air and even moisture to the roots in both wet and dry weather. High soil moisture offsets soil salinity and reduces the effects of high transpiration (makes wilting less likely). Compost will increase the amount of calcium available to the plants, I'm not sure if peat moss or pine needle compost will provide additional calcium in the same way, the acidity could also cause problems. Mulch heavily to slow drying.

2) Fertilizer: Provide phosphorus early in the season (planting hole etc) but hold off on Magnesium (Epsom’s salts) and high nitrogen fertilizer (organic or synthetic) until after fruit set. Commercial tomato farmers wait until midseason/after fruit set and then side dress the plants with nitrogen fertilizer. It boosts plant growth/health at the time the plants are growing the largest, and doesn't interfere with flowering or BER. It also prevents nitrogen loss from the soil through leaching and nitrification.

3) Early summer bright sun & hot days: Because high transpiration rates reduces calcium transport to fruits, selective well timed leaf pruning might be a good idea. Most of us get BER mainly with the first fruits of the season, and since it is a good idea to trim off the bottom leaves to aid airflow and reduce fungal infection anyway, it might be a good idea to wait until you have a good number of flowers and pea-sized fruit before trimming those big bottom leaves off (leaves below the first set of flowers; or about 1/4 to 1/3 of total leaf area). This will immediately shift the leaf to root ratio in favor of roots and boost the amount of calcium getting deep into the fruit. Reducing leaves will also reduce photosynthesis and slow fruit growth rate, thus reducing the need for calcium in the little fruits. So, with pruning you are attacking the problem from both directions. However this is probably best done only one time because the plant will grow roots in proportion to its leaf area/water needs, so repeated pruning will affect over all growth and production. Note: if you are growing determinant varieties only trim off some bottom leaves, do not sucker the plants because that will stop growth and production.

4) You may want to have your soil tested in general. Long term organic practices (large inputs of manure and compost, or wood ash for many years) can result in very high potassium levels, which affect calcium uptake. In this case, adding calcium can help both prevent BER and increase overall nutritional quality of the fruit. Yes, this is counter to number one above (add lots of organic matter), but life is complicated. Be careful to add the appropriate calcium source based on your soil pH (e.g. gypsum for high pH soil, limestone or dolomitic lime for acidic soil), or uptake of all nutrients could be affected.


List of factors and reason they promote BER

Below ground --Root environment:
Low Ca—Calcium is needed for proper cell development in fruit.
Low P—Potassium is needed for root growth and fruit development, most of the plant’s entire need is taken up while the plant is young.
High Mg, -- Magnesium competes with calcium for uptake by roots (competition is minor though), and it increases nitrogen/photosynthetic efficiency = leaf growth and fruit growth.
High N (particularly NH4), -- Nitrogenous ions compete with calcium for uptake by roots and nitrogen favors foliage growth over root growth.
High K, -- Potassium competes with calcium for uptake by roots.
High Na-- Sodium competes with calcium for uptake by roots, and displaces potassium within the plant (only relevant in irrigated desert areas and for people who are told to salt planting holes for better tomatoes).
High salinity (total salts) -- at high levels causes osmotic stress, inhibiting water uptake by plant, thus lowering turgor pressure.
Drought, --Reduces Ca availability (less water for it to be in) and increases salinity of soil water.
Water logging in the root zone, --inhibits root activity = Ca uptake.
Cold soil, -- inhibits root activity = Ca uptake.

Above ground -Leaf-shoot environment:
Low humidity-- increases transpiration thus reduces internal water pressure.
High air movement -- increases transpiration thus reduces internal water pressure.
High light --increases transpiration, increased fruit growth rate,
High temperature --increases transpiration, increases growth rate of fruit.

Thank you! Very thorough (and complicated ! ) -- a great resource for trouble-shooting and preventive actions.

Thank you. Good report. I have this problem with several fruit, but the vines are producing so many that some need to go anyway.

I am assuming these need to be plucked from the vine.

Also, I have Celebrity and BetterBoy side by side, and I think the BB's have more BER. Does variety make a difference?

These are also more prevalent on the tomatoes I am experimenting with growing "over the water", so wind, temperature, etc could be affecting them more.

That's good stuff, thanks for posting it!

EG

As far as variety goes fruit shape is the most important thing, with plum shape being most susceptible because of the internal structure of the fruit. For round fruited varieties, other things would come into play like how a given variety grows foliage in relation to roots etc. rather than an inherent weakness for BER, so I guess that under certain soil conditions one variety could be worse than another, or one variety happend to set a lot of fruit at a particularly bad time (weather conditions) for BER. If two varieties flower a week apart that could make a difference one year.


It might be a good idea to keep track of weather conditions early in the season and mark down when each plant starts to flower since it is in the first two weeks after the flower drops that BER "infects" the fruit.

My vines have lots of tomatoes, but I have plucked as many as 3 or 4 from a vine with BER. I have some tomatoes in some boxes (about 20 inches of new top soil) and some in my garden area. Probably more BER in the boxes than in the garden, but some in both. Of course, the boxes have more blooms, more fruit....primarily because of the rich soil, and more sunlight.

I do think that several of the "effects" you mention above could have been the case. We had cool days/nights and then SUMMERTIME, the plants took off. This is my first year with the boxes, and I am experimenting with how to water. I have the whole garden on an irrigation system, watering every third day. The boxes seem to drain well, they are sitting on the edge of my pier, over the water (lots of air, sun, and drying). Next year I may get them on their own system, or on a system that is every other day.

There are times when the plants seem to have had that "tough" look--healthy, but the stems and leaves a little dry and curled.

[img]https://i854.photobucket.com/albums/ab104/lakngulf/G2010May/G2010043.jpg[/img]

just stripped a plant completely tomatoless today...It was a german queen. Every single tomato... The weather's been pretty bad here. Cool spring to 103. TONS of rain to none for 8 days now. My may-moes are sufferring.

Looks like Yellow Bells are susceptible :
[img]https://i290.photobucket.com/albums/ll272/applesbucket/Image7365.jpg[/img]

It's very prolific though; this is only a handful out of dozens, I think I'll still get to can some yellow tomato sauce this summer.

So are Risentraube.
These are drought induced.

[img]https://i728.photobucket.com/albums/ww281/Ozark_Lady/100_2785_phixr.jpg[/img]

The 4 little guys are Risentraube, the others are OSU blue.

When I water daily, very few show up, but just miss one day watering, and there ya have it BER.
So far, this is almost the entire harvest for 2010, I did get 6-8 other tiny Risentraube. No other tomato is showing BER.
This drought is just taking out my garden totally. Actually, only the container plants are surviving, since they don't have to share water with the other plants, weeds, or tree roots.

Ozark Lady wrote:So are Risentraube.
These are drought induced.

[img]https://i728.photobucket.com/albums/ww281/Ozark_Lady/100_2785_phixr.jpg[/img]

The 4 little guys are Risentraube, the others are OSU blue.

.

Almost definitely drought induced, but the wrong end on most of them to be Blossom End Rot. More like some variant of green shoulders (black shoulders?) anyway the tops don't ripen up right and it is due to heat and drought and too much sun exposure. The one at the bottom with the little round hole is probably hornworm damage.

The OSU blue is basically a suntan. Wherever the sun hits the fruits it turns blue, once you peel the fruit it is red, with an occasional hint of purple.
If you look closely, you can see the tomato stem, where it shaded the tomato and left "a bikini line" for lack of a better description. So far, my blue tomatoes have only been the shoulders, or one side, never a truly blue tomato.

Hornworms are bad this year, I just sprayed tomatoes with Bt yesterday, I have plants without leaves, just overnight.

I know it is the drought, the weeds are just so dry, that mama hornworm doesn't lay her eggs on them, so I am getting more than my fair share of them!

I'm not sure what RBG was getting at but I was going to say the OSU is supposed to be dark and even a lot darker. I saw some on another site that are amazingly BLACK/BLUE!!!!


Oh to have some of those seeds.


Hint hint.

What I was getting at was that this is a thread on BER and OL said in her post they had BER (" When I water daily, very few show up, but just miss one day watering, and there ya have it BER. ") , but that's not what is going on. Makes a difference what you decide to do about it.

Don't know if others had seen this. But I had read on another site that throwing a small handful of crushed eggshell into the hole when you plant your seedlings will solve the problem. This leads me to believe what I read in the original post about it possibly being caused by a lack of calcium availability during fruit production. I had this problem last year but not in previous years. I'll be throwing in some egg shells for the heck of it. Don't know if it was calcium or our cray hotand dry weather last year, but the egg shells can't hurt that's for sure. And if I don't see any this year,I'll probably be saving ALL of my egg shells next year!

For those who lack calcium, you can throw in a Tums antacid at the bottom of your hole before you put in your little tom plant. It doesn't hurt the plant, it dissolves great and the plant has all the calcium for the growing season so it doesn't get BER.

I also throw in 2-3 pinches of Espom salts in the bottom as well.

I had a terrible problem with BER last year and am doing everything I can this year to prevent it. Last year I grew the tomatoes in a tilled, depleted field but tilled in some chicken manure before planting and mulched with lots of egg shells. Didn't help.

This year I am planting them in my good nurishe-for-years lasagna bed and putting in a little lime.

Does the TUMS addition really work? I will definitely be giving it a try. I have a lot of TUMS on hand!

I depend on my tomatoes for seed sales! I need good tomatoes. I managed to get enough seed from last year's BER tomatoes to keep it going but sold out quickly. I look for better things from my tomatoes this year.

Thanks for the TUMS tip! I am excited about trying it this year!

No matter how much calcium you add to the soil, if the pH is too high or too low, the plant won't be able to access the mineral. Have a soil test done first. Then add any amendments that are lacking.

Yes please read TZ's very thorough explanation of BER at the beginning of this thread. It is very rarely due to a lack of calcium in the soil. It is either a problem of the roots being able to uptake it oar the plant being able to transport it to the fruit. Providing extra calcium might help a bit to compensate for the difficulty, but it doesn't solve the problem.

And Epsom salts can make it worse (see TZ's post for the explanation).

Thanks for the information. I did skim a little of it. Not really a science detail person. I won't be getting the soil tested either. I'm more of a causal gardener and must keep it cheap. I am adding some lime this year, the Tums and some epsom salts later in the season and mulching. Any more "secrets" I can do that will help, easy and cheap?

I planted them in a new bed last year in a depleted field with just a little chicken manure tilled in. This year I will plant them in the good bed where I have not had BER when used previously, so I don't expect problems but will do the listed things above just to be safe.

Thank you all for the information!

I also have put in my tomato powder milk along with eggshells and banana peels. So far so good........

When I found BER on some of my tomatoes, I put a handful of dried milk (calcium) around the base of each plant and watered.
The next rush of fruits didn't get the BER.
I don't know if it worked or not, but it seemed to do it. I did this for many varieties of tomatoes last year and they all benefited from the extra dried milk.

I'm growing 8 different kinds of tomatoes....there's 2 that haven't fruited yet. I started these myself and were stunted. I'm frankly surprised they've grown at all but they look pretty good now. Anyway, of the 6 that ARE fruiting, I have only 1 plant that is BERing right now. I can't remember what kind it is. But I've noticed that this plant also really gets thirsty very quickly.

Hi all. Last year many of my tomatoes had BER. I simply sliced the BER part of the tomato off and ate them anyway...It was my very first time growing a garden and I couldn't imagine tossing my babies out They tasted fine.

Question is, was it ok (safe) for me to still eat them after cutting away the BER?

Thanks all!

ice

You are still here, aren't you? Yes, it is safe. The BER isn't a disease, it is just a physiological response to the conditions. It just spoils the quality of the tomato in that area.

rainbowgardener wrote:You are still here, aren't you? Yes, it is safe. The BER isn't a disease, it is just a physiological response to the conditions. It just spoils the quality of the tomato in that area.

In my experience, you have to get to them fairly quickly, or else they can spoil a little faster than an unblemished tomato. Not too difficult a chore for many!

I had bad BER problems the first year I gardended, but since then I've been adding lime to my holes when I transplant and I haven't had nearly as many problems with it. And that's in spite of the fact that I plant a good number of paste tomatoes.

Well, I suppose I am here physically Good to know though, that I don't have to toss the BER ones!

When you say you put lime in the holes, are we talking the fruit or mineral?

Thank you!

ice

mattie g wrote:

rainbowgardener wrote:You are still here, aren't you? Yes, it is safe. The BER isn't a disease, it is just a physiological response to the conditions. It just spoils the quality of the tomato in that area.

In my experience, you have to get to them fairly quickly, or else they can spoil a little faster than an unblemished tomato. Not too difficult a chore for many!

I had bad BER problems the first year I gardended, but since then I've been adding lime to my holes when I transplant and I haven't had nearly as many problems with it. And that's in spite of the fact that I plant a good number of paste tomatoes.

Ice...I mean the mineral. I just use pelletized lime - nothing fancy. I assume it works OK since my BER issues have been fairly minimal. And I assume it doesn't hurt the plants since mine grow really strong and out out good amounts of fruit. I figure that putting it in the holes when the plant is young helps the plant absorb it over a period of time, rather than just trying to treat as it happens.

Garden (or pulverized) lime will work faster than pelletized.

I do not add calcium to correct or prevent BER. For the most part, I only had the problem in the peak of summer when the plants would wilt in the middle of the day. I adjusted my watering times and it solved the problem. I actually have not had a problem with tomatoes grown in earthboxes since they have a reservoir and do not dry out. The only thing that does sometimes happen is that if the tomatoes get too much water, they crack more (can't stop the rain). Excess water when the fruit is ripening sometimes leads to blander fruit.

BER is a physiologic response to a relative lack of calcium. Rarely does the soil actually lack calcium. The soil can have a lot of calcium but it won't do any good unless the plants are able to absorb it. Most of the time what is really needed is to finesse the watering schedule. The real science is tweaking the water so it is not too much, not too little, and get it so it is just right.

Wow...so much good information. I have had black spots on my tomatoes and I thought it was some kind of rot as I usually just grow flowers. Now I feel informed and armed with usefull, practical knowledge on how to combat BER and that the fruits of my labor would still be safe to eat. Thanks all!

Linda

I fight with BER every year! Such good information in this post.

mostly I deal with soil flushing due to the heavy rains we get from time to time here in Alberta. I had two indeterminants last year get like 12-15 feet tall and nothing but BER... I nearly cried pulling a 5 gallon pail of compost off that plant.

I did lose one of my tomatoes already but the rest seem to be doing alright... so far....

Stay tuned !

I was doing some reading today and this guy recommended adding a cup of agircultural gypsum to every hole that you have a tomato plant to help prevent BER. I'm not an experienced gardener by any means. Last year I just fed my tomato plant water once in awhile and never had any issues. This year I have 4 tomato plants and 2 of them are suffering a bit from BER. Mine are all in the ground but my neighbour who has his 1 plant in a pot seems to be suffering quite a bit from BER. He also waters from the bottom of the pot up where I water directly into the ground. Mine are showing signs on some tomatoes but not nearly as bad as his are showing. Just curious as what would be the cause of this?

I don't think it is the difference between watering from the bottom or the top, I think it is the difference between containers and ground. Container growing is very different. Containers dry out much faster, so they have to be watered more frequently. In the process of daily watering, you are also flushing nutrients out of the soil. And even with daily watering, the small amount of soil in a container is going through a lot more wet/dry cycles, drying out and then getting lots of water. Inconsistent watering is one of the common causes of BER. For others, go back to the beginning of this thread and read the material that was posted.

The wet/ dry thing is one reason why very large containers are recommended for growing tomatoes - like 10 gallons for a full sized tomato plant - because that amount of soil doesn't dry out as fast.

I had a few slight BER problems this year. Surprisingly enough I didn't have any on my containers only a few in the garden.

I haven't had BER in years, but I have the tomatoes in 18 gallon pots so they are not as prone to drying out quickly and I tend to have a heavy hand watering. I don't give the tomatoes dolomite either. I haven't had any issues with BER in earthboxes.

"I don't give the tomatoes dolomite either. I haven't had any issues with BER in earthboxes."

I wish I could say the same. Last year was my first year growing in earthboxes, and also the first time I got BER.
I hope it will be better this year, the instructions call for adding new dolomite lime and there was some still left from last year in the aggregate. I know its not uneven watering because Earthboxes keep the water constant as long as the reservoir is filled daily.
Very frustrating. I just started my seeds this past weekend so I am trying to find the answers before the earthboxes get planted at the end of October.

I just reread this OP this morning, after I had my coffee, because I needed to be awake to understand it better. I want to thank you TZ, this makes it so very clear as to the why of BER. This is excellent, and I am bookmarking it.

TZ -OH6 wrote:I find myself having to take notes in order to keep the information straight when I read scientific papers, so when I dug out the following review paper on the topic I decided to summarize the relevant information and add some comments to tie the science talk to backyard gardening conditions and practices. The paper itself focuses on the cellular/physiological aspects of BER, which does not concern us gardeners, but it also contains quite a bit of background info that does concern us. However, most of that background is from BER problems in commercial greenhouses, conditions and practices very different from outdoor gardens exposed to the whims of Mother Nature, so their conclusions as to what works and doesn't work must be considered in that context.

I do suggest looking at the article as some of the figures are informative.

https://aob.oxfordjournals.org/cgi/reprint/95/4/571

https://aob.oxfordjournals.org/cgi/content/full/95/4/571

The article:
A Cellular Hypothesis for the Induction of Blossom-End Rot in Tomato Fruit
LIM C. HO and PHILIP J. WHITE*
Annals of Botany 2005 95(4):571-581

My synopsis for gardeners

BER is caused by multiple cellular problems in the distal end of fruits, which result from low available calcium at that location during the first two weeks of fruit development (just after the flower fades and falls away, when most of cell division and differentiation is taking place). Because of the low number and structure of transport vessels in their fruit plum-shaped tomatoes are more susceptible than round fruited varieties. BER calcium sprays [calcium chloride et al.] applied before the second week of fruit growth can help directly, sprays are the best way to control BER under the controlled conditions of a greenhouse [But other steps might be just as effective in the more variable conditions of an outdoor garden--TZ].

Calcium can either be restricted from entering the plant (soil-root conditions) or be inefficiently transported to the distal part of the fruit once in the plant. The latter is caused by above ground conditions affecting leaf water loss and photosynthetic rates.

BER can be induced by a number of growing conditions, such as low soil calcium, low phosphorus, high magnesium, high nitrogen (particularly NH4), high potassium, high salinity, drought, water logging in the root zone, cold soil/roots, and also low humidity, high light, high temperature and high air movement in the leaf-shoot environment. When soil calcium is plentiful roots may not be able to take it in efficiently when the soil is cold or waterlogged. Once calcium is in the plant it is dependent on high turgor pressure to get to the distal part of the fruit. If water loss/transpiration is high from the leaves turgor pressure is reduced in the plant. At its most critical low pressure the plant wilts because it can't get enough water to its leaves. Bright light, heat, low humidity and air movement contribute to high water loss.

Movement of water up from the roots is mainly driven by negative pressure formed by evaporation within the leaves, so the leaves are literally sucking water from everything below them including the fruits. Root pressure is a much weaker force and pushes water up into the plant. It is driven by the difference in dissolved substances between the internal water and the soil water. As soil dries the concentration of dissolved substances in the remaining soil water increases, thus reducing root pressure in the plant, high salinity in moist soil has the same effect.

In addition to water transport effects, bright light also boosts photosynthesis and thus fruit growth. This is bad if the rate of calcium entering the fruit is not adequate to support the increase in growth rate.


Here is my interpretation of that information as it regards garden growing.


Some scenarios for BER

1) Cold wet cloudy conditions suddenly change to warm and sunny conditions soon after fruit set. The plant ramps up fruit growth while cold oxygen starved roots can't take in calcium fast enough.

2) The garden is shallowly tilled/amended over more compact subsoil layer, and the soil is high in nutrients from pre planting fertilizer application. Shallow rooted plants grow big, and then hot weather hits on schedule in early summer just as lots of tiny fruits are forming. The big leafy plants suck all the water out of the top layer of soil, reducing their internal water pressure and starving the fruits of calcium.

3) You are growing in low calcium, high fertilizer conditions with fluctuating water availability. This often resembles a five gallon bucket of potting mix, or low quality hard dirt with little organic matter, or a sand box.

4) You are growing Roma/plum tomatoes under ALMOST perfect conditions.


If you are plagued by BER, what can you do other than spray the plants with an anti-BER calcium solution when the fruits are barely visible (0-2 weeks old)?

Because soil calcium is rarely critically low, and because you cannot control cloudy, rainy, sunny, hot, dry or windy weather here are some things that you can try without having to test your soil for pH-calcium levels.

1) Soil: Make sure your soil both drains well and is water retentive. This means deeply dug with a lot of organic matter so that it provides air and even moisture to the roots in both wet and dry weather. High soil moisture offsets soil salinity and reduces the effects of high transpiration (makes wilting less likely). Compost will increase the amount of calcium available to the plants, I'm not sure if peat moss or pine needle compost will provide additional calcium in the same way, the acidity could also cause problems. Mulch heavily to slow drying.

2) Fertilizer: Provide phosphorus early in the season (planting hole etc) but hold off on Magnesium (Epsom’s salts) and high nitrogen fertilizer (organic or synthetic) until after fruit set. Commercial tomato farmers wait until midseason/after fruit set and then side dress the plants with nitrogen fertilizer. It boosts plant growth/health at the time the plants are growing the largest, and doesn't interfere with flowering or BER. It also prevents nitrogen loss from the soil through leaching and nitrification.

3) Early summer bright sun & hot days: Because high transpiration rates reduces calcium transport to fruits, selective well timed leaf pruning might be a good idea. Most of us get BER mainly with the first fruits of the season, and since it is a good idea to trim off the bottom leaves to aid airflow and reduce fungal infection anyway, it might be a good idea to wait until you have a good number of flowers and pea-sized fruit before trimming those big bottom leaves off (leaves below the first set of flowers; or about 1/4 to 1/3 of total leaf area). This will immediately shift the leaf to root ratio in favor of roots and boost the amount of calcium getting deep into the fruit. Reducing leaves will also reduce photosynthesis and slow fruit growth rate, thus reducing the need for calcium in the little fruits. So, with pruning you are attacking the problem from both directions. However this is probably best done only one time because the plant will grow roots in proportion to its leaf area/water needs, so repeated pruning will affect over all growth and production. Note: if you are growing determinant varieties only trim off some bottom leaves, do not sucker the plants because that will stop growth and production.

4) You may want to have your soil tested in general. Long term organic practices (large inputs of manure and compost, or wood ash for many years) can result in very high potassium levels, which affect calcium uptake. In this case, adding calcium can help both prevent BER and increase overall nutritional quality of the fruit. Yes, this is counter to number one above (add lots of organic matter), but life is complicated. Be careful to add the appropriate calcium source based on your soil pH (e.g. gypsum for high pH soil, limestone or dolomitic lime for acidic soil), or uptake of all nutrients could be affected.


List of factors and reason they promote BER

Below ground --Root environment:
Low Ca—Calcium is needed for proper cell development in fruit.
Low P—Potassium is needed for root growth and fruit development, most of the plant’s entire need is taken up while the plant is young.
High Mg, -- Magnesium competes with calcium for uptake by roots (competition is minor though), and it increases nitrogen/photosynthetic efficiency = leaf growth and fruit growth.
High N (particularly NH4), -- Nitrogenous ions compete with calcium for uptake by roots and nitrogen favors foliage growth over root growth.
High K, -- Potassium competes with calcium for uptake by roots.
High Na-- Sodium competes with calcium for uptake by roots, and displaces potassium within the plant (only relevant in irrigated desert areas and for people who are told to salt planting holes for better tomatoes).
High salinity (total salts) -- at high levels causes osmotic stress, inhibiting water uptake by plant, thus lowering turgor pressure.
Drought, --Reduces Ca availability (less water for it to be in) and increases salinity of soil water.
Water logging in the root zone, --inhibits root activity = Ca uptake.
Cold soil, -- inhibits root activity = Ca uptake.

Above ground -Leaf-shoot environment:
Low humidity-- increases transpiration thus reduces internal water pressure.
High air movement -- increases transpiration thus reduces internal water pressure.
High light --increases transpiration, increased fruit growth rate,
High temperature --increases transpiration, increases growth rate of fruit.

I think part of the problem with BER besides the environmental ones have more to do with variety. Some varieties are just more prone to it.

I struggled with BER the past 3 years in beefsteak tomatoes, cherry tomatoes were fine. Tried adding dozens of crushed eggshells but still did not help last year. I'll settle with the cherry toms!

A handfull of woodash for each plant is said to be good against this problem and a few others. Too much nitrogen is said to be bad for not getting BER, it gives less harvest anyway so its a generall good practice.
High temperatures makes the BER worse as well as bad air circulation. Its more common in greenhouses atleast where I live. So I think that you who live in really humid areas might have bigger troubles than others allthough I havent had any problems with this my self (quite high humidity here in Sweden and it has gotten higher lately.) To my understanding the flower due to high humidity stays on the fruit instead of falling of like it naturally would/should.
What is exactly causing this to happen seems to differ depending on who you ask, and probably there are a few different factors?

As imafan26 said the genetic diversity is not only shown in shapes and flavours, but also resistance to diseases or not. So I would try other varieties if keeps getting the same problem with a specific variety.

sime: eggshells are slow release even crushed, so it may not have had time to do much of a difference.