Originally posted by jbwhttail:
Blossom end rot happens because of one of two conditions.

1. If it is on first fruits, it is because of plants set out too early and ground was too cold. Later fruits should be ok.

2. The most common cause is hot dry weather, the fruit is not getting enough moisture. Water the plant early in the morning and soak both leaves and ground. You don't want moisture overnight as it tends to give your plants fungus which is worse than the end rot. If you till between rows of tomatoes don't till more than 1" deep, breaking the root system also will hinder the plants ability to get enough water to make fruit.