Green tomatoes turning brown on bottom - blossom end rot by: Nance
When tomatoes turn brown at the ends it's because of blossom end rot. The rot is all brown and watery, then goes dark and hard. You will have to pick those tomatoes and toss them.
I understand it's a mineral, mostly calcium deficiency, or the plant is stressed and can't take up calcium from the soil. Stressing could have been caused by erratic watering, and really cold or hot temperatures. When these happen as the flowers are setting fruit it then causes blossom end rot on the fruit.
Best action now is to have even fertilizing and watering. Also next year don't subject your little plants to the cold too early, and put mulch on to keep water levels stable and temperatures even. Nance
