Roma Tomatoes Disproportionately Affected by Blossom- End Rot

Blossom end rot on Tomato in Chicago garden.png

The most common question I'm fielding on the internet has to do with blossom-end rot of tomatoes (BER for short). Diagnosing this tomato problem for gardeners is easy enough, but after diagnosing it for people they want to know why it is seems to only be affecting their Roma tomato plants. 

After searching the internet and not being satified with the answers I found, I decided to turn to the closest thing to a tomato expert that I knew. My friend Colleen who writes at OrganicGardening.About.com and is a tomato freak. If anyone was going to know the answer or at least point us in the right direction it was going to be Colleen. 
Here is transcript of the Email between Colleen and myself on the subject of blossom-end rot on Roma tomatoes. 
[MBT] Everyone and their mother is asking me about BER. One thing that everyone seems to have in common is that it is happening on Roma tomatoes. I've Googled and many sources say that Romas are suseptible to BER, but nobody really explains why. Genetic? Something to do with the root structure of Romas (my guess) or something else?
[CV]

I get it on my Romas, too, but also on 'Polish Linguisa' and 'San Marzano,' which are also elongated, paste-type tomatoes. You're on the right track with the structure question, but from what I've seen, it has more to do with fruit structure than root or stem structure. The research I read (you can read it here) seems to suggest that because BER occurs during periods of rapid fruit expansion, and because elongated tomatoes seem more susceptible to it than other tomatoes (and cherry tomatoes never get BER) that the elongated shape of Roma-type tomatoes is to blame. The idea is that calcium deficiency within the fruit structure itself is to blame, and that vascular walls in elongated tomatoes are less capable of transmitting adequate calcium levels to the blossom ends of the tomatoes. To test this, the researchers used a calcium spray (which I had always considered to be a crock, btw)  on the blossom end of Romas, being sure to spray before any evidence of BER was present. On those Romas that received the calcium spray applied to the blossom end, BER was greatly reduced as compared to fruits that the calcium spray hadn't been applied to. So the idea is that because the cell walls of the tomatoes were able to absorb the calcium spray, BER was prevented -- suggesting that BER in Roma type tomatoes has a lot less to do with levels of calcium in the soil (or watering practices) than with the shape of the fruits themselves.

It makes sense, especially when you consider that I can have whole periods of zero blossom end rot on my tomatoes, but my Romas and Polish Linguisas are rampant with it. The plants are in the same soil, getting the same fertilizer, same watering schedule, same mulch -- the only difference is fruit shape. I'd like to see someone graft a Roma plant onto the rootstock of a non-Roma to see whether the roots have anything to do with it or not -- seems like it would be easy enough to do, I just haven't seen anything about anyone doing it yet. 
Thanks for supplying the answer, Colleen. If you're growing Romas, or other paste type tomatoes, and are battling BER it may have little to do with your skills at growing tomatoes. The real culprit seems to be the shape of the fruit. Remember, blossom-end rot is not a tomato disease. 

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  • I get it even on other shapes of tomatoes... though, as you say, never on cherries, which is why over the years, I gravitate towards the smaller 'matoes. Gardening with kids means I *need* tomato success, despite the sacrifice of never growing the big, glamourous heirlooms.

  • Other shapes of tomatoes (again, besides cherries) definitely get it, but it seems to have more to do with the traditional reason we've all heard for why tomatoes get BER: either too much/too little water during fruit production, or inadequate levels of calcium in the soil. Romas are just more of a pain that way than others.

    I make sure to grow plenty of cherry and grape tomatoes exactly for the reason you mention, Jennifer -- my kids love tomatoes and we better have some or I won't hear the end of it ;-)

  • I'm growing Marzano for the first time this year--will watch for BER; I'm not really worried about it, I just like to try diff types of tomatoes. Love the research, would love to be a hort geek conducting those experiments!

  • I always save eggshells for a few weeks before planting the tomatoes, and crush one eggshell per tomato plant. I put the eggshell in the planting hole and mix it a little with the soil. I've never had blossom end rot on any variety of tomatoes I've ever grown.

  • Hmmm. . . never had early or late blight either, not even last year. Last year since the soil was new, it kind of makes sense, but I think blights also spread via the air. I've never had a veggie bed big enough to rotate tomatoes every three years as the experts recommend, either. I mulch, but rarely water the veggies, and I've rarely had cracked tomato skins. I don't know if the eggshells have anything to do with no blight and rare cracked skins, but I do know tomatoes like calcium.

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