Blossom-end rot occurs because there is a problem of calcium transport, getting enough calcium to the tomato fruit. The reason they rot is because of low calcium in the cell walls.” – University of Nebraska extension.
Whether you are a well-seasoned tomato grower or first season newbie, you are eagerly awaiting the taste of that first hand-picked juicy tomato fresh from the garden. As you are carefully checking and grooming your plants and notice a flat bottom, brown spot on some of your tomatoes, disappointment is putting it mildly. Considering the challenging heat and drought conditions we have been experiencing, this is no surprise. It occurs more frequently in early fruit, so may adapt on its own. University of Nebraska extension has observed susceptibility on Better Boy and Big Beef varieties and more resistance on Mountain Delight, Mountain Fresh and Mountain Spring. In our garden, we have noticed more susceptibility on romas and other paste varieties.
The good news is this condition is not a viral, bacterial or fungal issue, so it will not spread. It is a calcium deficiency usually induced by fluctuations in plant’s available water supply. High temperatures encourage rapid cell growth in the fruit and the tomato plant can’t uptake calcium fast enough. If the roots are crowded or pruned while hoeing, the stress will also increase blossom-end rot. Tomatoes prefer soil pH of 6.0 to 6.7. If your soil pH is higher, you may adjust it by adding gypsum or lime. Applying too much at one time can have adverse effects.
The biggest factor is drought stress and wide fluctuations in soil water. In general, the recommendation is 1 ½ inches of water a week. But with as little rain as we have had with excessive heat, they probably require more. Getting the water directly to the roots with drip irrigation is more successful than overhead sprinkling. Water early in the morning. Some gardeners have had success with placing an inverted liter plastic bottle with holes in it along with each tomato start at planting time. This will give each plant a continuous water source at the root level. Mulching with pine straw, straw, or newspaper will conserve moisture.
When you notice a tomato with the signs of blossom-end rot, you may as well just compost it. It doesn’t hurt to remove the bottom half and eat the rest, although the texture may be affected. But the tomato will not heal itself and will only get progressively worse. Other crops that are susceptible include peppers, summer squash, eggplant, cucumbers and even watermelon. We have had better results including a handful of crushed eggshells in the planting hole of all these species. Then later when the plant is setting a second set of tomatoes, we sprinkle more eggshells around each plant. This is necessary because according to Mother Earth News “calcium is non-mobile in the plant once it is imported”. Mother Earth recommends a treatment of poking a calcium carbonate tablet (like Tums) at the base of a struggling tomato plant. This is most effective at the first sign.