How to prevent blossom-end rot in tomatoes.

As the name implies, blossom-end rot (BER) is a deformity that occurs at the blossom end of all fruiting vegetables. It is particularly common in tomatoes, squash, and pepper plants. BER begins as a watery-looking area adjacent to the blossom. In time, the lesions enlarge, become brown to black in color, and take on a leathery appearance, which covers the bottom half of the fruit. While edible, the unaffected upper half of the fruit is small and not worth keeping. BER is not caused by a pest or parasite; rather, it is the result of a calcium deficiency in the plant. All plants require significant quantities of calcium to develop correctly, and BER is a sure sign that the plant is not absorbing enough of the mineral for the proper development of fruit. There are two primary causes of calcium deficiency in plants. The first results from a calcium deficiency in the soil. The soil simply does not contain enough calcium to meet the needs of the plant. Alternately, soil conditions are such (usually too wet or too dry) that the plants cannot absorb enough calcium to meet their needs. As usually is the case, an ounce of prevention is worth a pound of cure, so begin your program to prevent BER by making sure the soil in your garden is not deficient in calcium. One can add lime, gypsum, and eggshells to increase the calcium content of soils thought to be deficient in the mineral. Eggshells are an excellent safe source of calcium for plants, but it takes a fair amount of time before the calcium in eggshells becomes available to the plant. Lime and gypsum must be used with caution because both materials may make the soil too alkaline for ideal plant growth. I prefer to add ground-up oyster shells yearly to my garden soil at the rate four to six pounds per one hundred square foot to make sure the soil does not become calcium deficient. Now, the hard part. Even if your soil has sufficient calcium, the plants will not be able to absorb the mineral if soil conditions are not right. In this respect, plants may not be able to absorb sufficient calcium if the soil is either too dry or too wet. This is particularly true of the tomato plant, which should be managed on the dry side. Most gardeners tend to over-water their tomato plants. Tomatoes, as garden guru Bob Tanem advises, should be given infrequent deep watering only when they show signs (wilting) of water deficiency in the morning. Now what can you do if your mature plants are developing fruit with BER? At this point, it is too late to amend the soil, and changing your watering habits probably will not make much difference either once the fruit has set. So what, if anything, can you do to salvage what remains of the crop? Liquid calcium sprays provide the only known remedy for this gardening dilemma. Products like Bonide’s Rot-Stop can provide emergency treatment to plants that are, for any reason, deficient in calcium. There is some question as to whether the commonly sold calcium sprays are organic. Thus, it is best to make sure the soil has enough calcium from natural sources like ground-up oyster shells to prevent the condition from occurring in the first place. However, if your mature tomato plants are producing malformed fruit showing BER, a liquid calcium spray will provide a quick fix for the problem. You also can make your own calcium spray by filling a gallon jar with eggshells and water and letting the mixture steep for a month. Filter out the eggshells and use the resulting liquid as a foliar spray, one cup per quart of water. The problem with this way of treating BER results from the fact that it takes a month to produce the calcium spray; thus, unless you anticipate the problem well ahead of time and have the eggshell spray ready for use when you need it, you will be forced to buy a commercial product even though it might not be as organic as you would like. Finally, I should point out that researchers at the University of Nebraska have determined that calcium is not absorbed through the leaves of a tomato plant. They maintain that the only way to prevent BED in tomatoes is to make sure the soil, with respect to pH, water content, etc., is adequate to allow the plants to absorb calcium through the plants’ root system. This is an excerpt from my soon to be published book Gardening The Organic Way.