- Extreme fluctuations in soil moisture, going from very wet to very dry (I think we're all experiencing this...)
- Rapid plant growth early in the season, followed by extended dry weather (Sound familiar?)
- Excessive rains that smother root hairs
- Excess soil salts
- Cultivating too close to the plant
The first few of these conditions are definitely present in our summer growing season. With the extreme heat and drought that we've had, this blossom end rot is quite common.
To prevent this rot from occuring in the future, you need to try to keep the soil moisture consistent. This can be done by altering your watering habits, as well as by mulching your vegetable garden. Also, avoid using fertilizers that are really high in nitrogen or using lots of fresh manure.
For more information on blossom end rot, and other tomato problems, check out Tomato Dirt.com.