Last week I was looking at my one, nice-sized tomato on the Pruden’s Purple tomato plant. I knew it was cat faced, as early tomatoes often are. Cat facing is a problem with pollination caused by weather conditions. When I looked at that tomato again, I noticed it had now developed a bad case of blossom end rot (BER). My experience is the BER allows disease like fungal rots to penetrate the tomato and spread throughout before the tomato gets a chance to mature and ripen. So I removed and tossed it so the plant can put its energy into hopefully healthy fruit.
BER is a common nuisance and we gardeners spend a lot of time trying to avoid it, although what causes it is kind of a mystery. You hear all kinds of theories and advice. It’s a lack of soil calcium, a problem with calcium transport, too much nitrogen, too little or too much water, soil pH, yada yada. To prevent it add lime, add egg shells, add bone meal, add Epsom salts, spray with calcium, water more, water less, water consistently, and so forth. Paste tomatoes and some heirlooms seem to be particularly prone to it. I just try not to think of it and hope it does not happen, because all the advice seems to be all over the place and I doubt any of that is really going to help.
Coincidentally, I read an interesting article on BER in the UMass Extension Vegetable Notes newsletter. They excerpted an article by Gordon Johnson of the UDel extension service. Rather than excerpt their excerpt, you can find the UMass newsletter at this link so you can read it for yourself. The article does a good job of explaining what can cause BER. If you understand that, you can hopefully speculate what might be happening in your garden. All of the suggested causes above have some truth to them, but as you might expect, it is complex.
Calcium is an essential component of plant cell structure. Lack of sufficient calcium in the cells at the blossom end of the fruit, farthest away from the stem, is what causes BER. In fact, all parts of a growing plant need calcium, it is just harder to transport it to the growing end of the fruit (the blossom end) and if the quantity is not adequate., the cells collapse, resulting in an ugly scar. There are many reasons why this could be the case. Calcium must be absorbed by the roots and transported in its ionic form, as the cation Ca++. To get calcium to an area, there has to a flow of water through the plant’s vascular system. Anything that disrupts the quantity of calcium or water flow can cause problems.
Some possible causes can be:
- Reduced absorption of calcium by the roots. The soil pH may be too low (less than 5.2), or there may be competing cations (e.g., ammonium, potassium, phosphorous), or there can rarely be a lack of sufficient calcium in the soil. Lime can correct the pH and supply problem. Do not over-fertilize and avoid ammonium and urea fertilizers to help reduce competing cations.
- There can be competition for water and minerals within the plant. A rapidly growing plant (as happens in the spring and early summer) will preferentially use its resources to build the plant structure (leaves and stems) rather than fruit.
- There may be insufficient water flow through the plant. The soil may be too dry, too wet (reduces soil oxygen which impairs root function), compacted, root pests or pathogens, or high soil temperatures. If vascular flow is reduced, so is the transport of minerals.
- A lot of water flow is used to support transpiration, the evaporation of water from leaves that cools the plant. The parts that transpire more (leaves) will receive more minerals along with the fluid. Fruits transpire very little so get less. Humidity can also affect transpiration, with high humidity reducing it considerably. Plants covered with row cover have less air flow over them and consequently less transpiration happens.
See, I said it was complex. What it boils down to is: make sure plants and roots are healthy and actively growing, soil pH is within range, plants are not over-fertilized, and water is applied adequately and consistently, which of course is what we all try to do. After that, it’s out of your hands, unless you think your egg shells or Epsom salts or whatever really works. Then do that.
Artistic note: I do not have a photo of a tomato with BER I could use. I usually just toss those tomatoes in the compost, why would I want to photograph my failures? I looked for public domain photos but they were all butt ugly. So I used a photo of my Pineapple tomatoes grown in 2014, showing some cracking and cat facing but no BER. Hooray. Just shows my method of avoiding the whole subject works pretty well.