Blossom End Rot
Sometimes, you'll find tan-colored, water-soaked lesions on the bottoms of your fruit (where blossoms were), which can enlarge and turn black an leathery. This is likely caused by a combination cold temperatures or extreme heat during the blossom period and variations in watering. These conditions keep the plant from getting the calcium it needs for its fruit, and to fix this, you'll need to water and fertilize regularly. Mulching should help avoid extreme fluctuations in water supply.