I seem to spend a lot of my time, at this part of the season, looking at my tomatoes from underneath – the blossom end!
Discovering that your tomatoes are affected by Blossom End Rot (BER) is one of the most frustrating experiences when growing tomatoes.
They look great from above, but just as they are about to be picked and eaten, you find that the fruit are suffering from black/brown leathery patches on the underside – what a big disappointment!
The tomatoes above are so badly effected, they are useless! I’ve had seasons when almost every tomato on a plant was affected by BER.
Hopefully, this article should help youunderstand Blossom End Rot and how to avoid it next season!
So what is Blossom End Rot?
BER is a calcium deficiency. As a tomato grows, calcium is required to develop the fleshy wall inside the skin.
If calcium runs out or the supply of calcium is interrupted, a dark leathery patch will form in the growing area where calcium was absent. This is normally the underside or blossom end of the tomato.
Availability of calcium is the key to avoid BER
In order to avoid the problem, we have to make sure that calcium is available at all times, without interruption, when the fruit are swelling.
This can be quite difficult to achieve given the many different circumstances in which tomato plants are grown and unpredictable weather conditions and temperatures – all of which can effect calcium uptake.
Translocation – Moving nutrients from lower leaves to the growing tip and fruit
When more magnesium is needed by the growing tip or fruit of a plant, than can be absorbed by the roots, extra magnesium can be taken from other parts of the same plant – usually the lower leaves.
Some nutrients are mobile
Some nutrients move around a plant’s system quite freely such as nitrogen and magnesium and are able to be moved to the areas of greatest need – usually the growing tip. These are called mobile elements.
Calcium is immobile
However, nutrients such as calcium and Iron are immobile and are unable to move from one part of a plant to another.
The only place that a plant can obtain calcium, when more is needed, is directly from the soil.**
Plants cannot move calcium from lower leaves to growing tip if required, as nitrogen or magnesium is able to be moved.
This means that even a short interruption of calcium from the soil may result in BER.
This process of moving nutrients around a plant’s system is sometimes referred to as translocation. Calcium cannot be translocated.
Dry soil is nutrient barren
Roots can only absorb nutrients when nutrients are dissolved in water.
If the soil is dry, a plant will be unable to absorb nutrients and calcium intake will be interrupted. However, the mobile elements such as magnesium may be moved from lower leaves to the growing tip when there is a shortage, but this cannot happen with calcium because, as already explained, calcium is immobile.
A good reason to keep soil moist and not allow it to dry out. When the calcium supply is stopped, even for a short time when the tomatoes are swelling, BER is likely to appear.
Some advice doesn’t explain why!
When I first started growing tomatoes I was bugged by the advice: “Keeping the soil moist helps avoid Blossom End Rot”. It seems a rather unclear piece of advice!
It was some years later before I understood that BER is a calcium difficiency and calcium is an immobile nutrient or element.
Still, had it not been for calcium, and my desire to understand and pass on the information, I don’t think I would have started the Tomato Growing website and Newsletter.
Next week, in part two, there’ll be tips and suggestions on how to foliar feed** to help avoid BER.
I hope that many of you are tasting the results of your hard work (or soon will be!).
See also: Blossom End Rot – Part Two