Blossom-End Rot, a.k.a. BER, is not a disease, but the result of a calcium deficiency that is usually caused by inconsistent watering. Both drought conditions and over-watering from irrigation, heavy rains or even high humidity levels can cause your tomato plants to suffer from a calcium deficiency and BER. It is also thought that highly acidic soils contribute to this condition and any damage to the roots caused by severe root pruning or improper transplanting can also have the same results, so handle those roots carefully.
Blossom-End Rot can be recognized by a leathery, brown rot developing on or near the blossom end of the tomato. Normally starting with a brown lesion about the size of a dime, it will increase in size as the condition gets worse. Over time those lesions may become covered with a black mold. BER not only affects the quality of the fruit, but can affect the quantity as well.
There are some fairly simple steps that you can take to reduce the possibility of Blossom-End Rot:
- Make sure to provide adequate water. While putting on fruit, tomatoes need about 1.5 inches of water a week. You may need to increase this during very hot times, watering in the early morning to prevent leaf burn. You may also have to decrease water during periods of heavy rain. If you are not sure how much water your tomatoes are getting, place a coffee can or other similar sized container near your tomato plants but unobstructed. You can then measure the amount of water mid-week and adjust accordingly. A more precise means of measurement is a strategically-placed rain gauge.
- Using mulch will conserve moisture. You can use newspapers, straw or rubber mulches.
- Tomatoes grow best and the incidents of BER are reduced when you keep the soil pH between 6.0 and 6.5. A soil tester is one of the best tools a gardener can have in his or her arsenal. The lower end of the pH scale represents more acidic soil while the higher end of the scale is indicative of more alkaline soil. 7.0 is the neutral point. You can decrease the pH by adding sulfur, which is approved for organic gardening, or by adding compost or other organic matter, which takes longer but builds soil quality as well as reducing the need for additional fertilizers. Soil, over time, will revert back to its natural state, so periodic soil testing is a good idea. Organic limestone is the most common additive to raise the pH in your soil. Some lime may require adding prior to planting, so read those package directions carefully. Wood ash is also effective, but it breaks down quickly which can result in over-application, which can be devastating to your soil.
- Apply fertilizers or essential nutrients properly and with care. Over fertilizing can bring on BER. Soil testing is the only fool-proof way to insure proper fertilization.
If your tomato plants develop Blossom-End Rot, you can treat them by spraying them with a calcium solution at the rate of 4 level tablespoons per 1 gallon of water. You can use either calcium chloride or calcium nitrate, but be aware that when temperatures are higher than 85°F calcium chloride can burn your plants. You should spray 2-3 times per week, starting as the second fruit clusters are blooming.
It is also true that some varieties of tomatoes are more susceptible than others. It might be to your benefit to grow a number of varieties, making notes on which tomato plants perform best and have the fewest incidents of BER and other issues. When making notes, also note the weather conditions, as these can also affect how your garden grows. Taking this simple step will insure that you grow the best varieties for your soil and for your climate, insuring a most bountiful harvest.