Vine-ripe tomatoes are a major incentive for gardening.
The promise of flavorful vine-ripe freshly picked tomatoes is one of the main reasons people want to have a home garden. Imagine the disappointment when fruits begin to develop a black spot on the bottom that ruins the tomato. The problem is blossom-end rot. It is not a disease, but a deficiency of calcium Calcium is important in forming cell walls, so when the tomato lacks calcium the tissue breaks down. There are a number of reasons calcium deficiency occurs. Calcium chloride sprays can help prevent blossom-end rot if begun early enough.
Predisposition of Tomato Plants
Tomato leaves take up more calcium than the fruits.
Just from how they grow, tomato plants tend to have less calcium in the fruits. Calcium is taken up in water from the roots, and goes first to the leaves, which are losing water rapidly through their tiny breathing pores called stomata. The tomato fruits have a waxy skin and not much water loss, so not as much of the water and calcium goes to the developing tomato. When other factors interact with the naturally slower calcium uptake in the fruits, tomato blossom-end rot can develop.
Factors in Developing Calcium Deficiency
Tomato fruits need adequate calcium.
Calcium-deficient soil results in calcium deficiency in plants. Soil pH affects the availability of calcium to the plant. Tomatoes prefer a pH of 6.0 to 6.5. If the soil is more acid than that, tomatoes can't take calcium up. Not enough water in the soil at any time leads to calcium not reaching leaves or fruits. If too much nitrogen-rich fertilizer is applied, leaves become more numerous and faster-growing, and take up even more of the available calcium. Sometimes the bottom of the fruit grows faster than the rest, leaving that area without calcium.
Prevention
Although calcium chloride can be sprayed on tomato plants to help with blossom-end rot, it is preferable to address the basic problems responsible for the calcium deficiency. Test the soil for calcium and pH level. If calcium is needed, apply calcium nitrate at a rate of 2 pounds per 100 feet of row. If pH is too low, apply gypsum at a rate of 1 to 2 pounds per 100 square feet. If soil calcium and soil pH are good, make sure tomatoes have adequate and even water conditions. Don't apply high nitrogen fertilizers. Remove any fruits that are affected by blossom-end rot so they don't take up nutrients that could be used by good fruits or allow bacteria and fungi to enter through damaged areas.
Calcium Chloride Application
Calcium chloride is sprayed onto tomato leaves, which absorb the compound. Spraying it on the fruits has no effect, because fruits can't absorb calcium chloride. Spraying has to be done before fruit damage is seen. The spray will not help to recover damaged tomatoes. Watch when the first fruit clusters are forming and start spraying leaves if any signs of blossom-end rot are visible to prevent further damage. The spray can harm plants if it is put on when plant is under any stress such as that from underwatering. Calcium chloride can burn plants if it is applied when air temperatures are greater than 85 to 90 Fahrenheit. Spray plants once a week, preferably in late afternoon. Rates of application are 4 tablespoons per gallon of water for 95% calcium chloride and 5 tablespoons per gallon of water for 78% calcium chloride.
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