Blossom End Rot is the bane of my summer tomato garden. I am picking and composting at least a dozen tomatoes a day, all suffering from a brown, rotted bottom. It's incredibly discouraging.
So, so many people believe that BER is caused by calcium deficiency in the soil. As you will soon see, the problem is not that simple. However, I went ahead and tested my soil. It has plenty of calcium, probably because I add our own crushed eggshells from the compost bin into my beds every year; and though it takes a long time to break down, it does eventually become available to the plants. Just to be sure, this year, I also buried two Tums tablets at the base of each plant, under the drip line holes, so they'd dissolve and add extra calcium to the soil. This was recommended procedure in one of my college courses, so I proceeded, even though I was doubtful.
I've also read time and time again that BER is also a water problem, with the way calcium moves through the plant, and that water stress can cause BER. We are watering every day, since it's been hot - the beds get 20 minutes of drip each morning.
SO: The beds have even, consistent moisture. The calcium is there in the soil. I even tried some hybrid tomatoes this year in the hope that they would be resistant. To no avail, it turns out - they have just as many affected fruits as the heirlooms.
BUT all is not lost. I've noticed something interesting this year.
I only get BER on the long, thin paste tomato varieties. Not on the ones like those pictured here, that are chunky and full.
So, noticing that, I started typing different sorts of queries in to Google, with altered words and phrases. And I found the most excellent article from our very own UC division of agriculture and natural resources (UCANR). This article spells it OUT, my friends. Here's some of what I learned, though I recommend reading the entire article if BER is a problem in your garden, too:
It turns out that BER is more common in fast growing varieties with extensive leaf systems. It does affect the more narrow fruits like Roma, and it also tends to affect determinate tomatoes more, as there is pressure in the plant to ripen all the fruit at once.
While BER is a calcium issue, it's not as simple as just adding calcium to the soil. And while at heart BER management is a water issue, it's not a simple as keeping an even amount of moisture in the soil. Here's how it works. Calcium is dissolved in the soil (by all those little critters in the microbiome - fungi, especially) and is taken up by the plant root and is transported in the xylem in the plant stem (the 'tubes' that transport water; remember your 9th grade biology? Phloem transports the nutrients. But calcium is mobile in water and goes through the xylem only). And then: "Under conditions of high evaporative demand, i.e. low relative humidity and high temperature, water moves rapidly to the leaves, where most transpiration occurs. The calcium is carried along with the water, so most calcium absorbed by the plant ends up in the leaves. Fruit do not transpire as much as leaves; therefore less calcium reaches the fruit, which can cause a localized calcium deficiency." Um, low relative humidity and high temperature? This sentence may as well have a map with a pin in it in Walnut Creek, CA.
And not only that, once the fruit develops its waxy cuticle (when the fruit is between 1/2 - 3/4" in diameter), the transpiration rate in the fruit is FURTHER reduced. And get this, transpiration can also be restricted in cool or cloudy weather because the atmospheric demand for moisture is low. So that's why we shouldn't be planting our tomatoes too early, especially when the soil is too cold!
Now, we had an extraordinarily chilly May. Which actually often happens, especially the first half of the month. And it happens after a heat wave in April, which gets us all anxious to get tomatoes in the ground. And then it turns cold again. Then we had several blasts of very hot weather, which makes everything transpire even more. So the leaves are transpiring like crazy, but the fruit is of a certain size now and can't transpire. So no calcium to the fruit. WHICH EXPLAINS why the fruit on the side of the garden that is getting mid-day shade isn't having nearly as much BER. It's not transpiring as heavily on those very hot days as the ones on the mid-day full-sun part of the garden!
The article ends with a checklist of things you can do to prevent/manage blossom end rot, like adding organic matter to the soil, mulching heavily, watering on a schedule, etc, all things I already do. What's that definition of crazy again? Doing the same thing over and over and hoping you'll get a different result? Seems to me I need to change things up next year. Like for instance, plant tomatoes in the ground LATER, like mid-May, and maybe even more importantly, avoid planting narrow-fruited varieties! I mean, look at the pictures of those fabulous thick tomatoes all through this post! Both of these varieties (Italian Heirloom and Hungarian Heart) can be used as dual-purpose tomatoes, for both eating fresh and for cooking or canning. So from now on, I'm sticking to the fattest tomatoes I can find.