Tomatoes with blossom-end rot look like an animal or insect devoured the fruit, but don't blame the bugs for the problem. Calcium deficiency is the root cause of blossom-end rot in tomatoes and other plants such as squash. Taking care of the problem with home remedies is possible, if caution is used. Too much of anything in the garden can become toxic instead of beneficial.
Blossom-end rot occurs from a stint of too rapid growth from by extremes of watering, using a fertilizer with too high of a nitrogen level or a lack of calcium absorption from the soil. Extreme rain or drought conditions, the wrong fertilizer and a lack of natural calcium in the soil can all contribute to blossom-end rot developing in tomato plants. The plant at the end opposite the stem begins to develop a small spot that enlarges and rots.
Once a tomato develops blossom-end rot, that fruit must be picked from the plant and discarded to prevent it from becoming a drain on the plant's resources. Reversing the condition is impossible, but blossom-end rot can be prevented in other tomato plants in the area through effective soil maintenance. Check the pH level of the soil with a test kit from a garden center. Amend the soil to maintain a pH of 6.0 to 6.5. Wait two months before planting another tomato crop. Use a regular watering schedule, and ensure the plant has 1-1/2 inches of weekly water while tomatoes are on the vine. Cover the soil with mulch to keep the moisture from evaporating from the ground.
Because blossom-end rot can be a calcium deficiency issue, many recommend putting powdered milk on the soil or watering the tomato plants with milk. This home remedy poses the problem of a smell from dried and warmed milk used outside in the garden. Milk, though an important source for calcium for humans, is not effectively absorbed by tomatoes to counter the lack of calcium in the plant, according to Marianne C. Ophardt from Washington State University Extension.
Send a sample of the soil to the county garden extension for soil testing to determine if there is calcium deficiency in the soil. Spray applications on the tomato plants of calcium will not be absorbed by the plant, but supplementing the soil with calcium from crushed egg shells will help prevent blossom-end rot in the future. The Clark County Master Gardeners in Washington State recommend mixing four crushed egg shells into the soil around each tomato plant at the beginning of the planting season.