Blossom end rot is often caused by too much nitrogen in your soil and a possible calcium deficiency. Water plant consistently and only as needed. (If you poke your finger in the top inch and half of soil and the soil is dry water your plants)

Check your Ph it should be between 6.0 and 7.0 because these products all make your soil more alkaline. You can add small amounts of egg shells, egg tonic, gypsum or rock phosphate (green sand), wood ashe (lime is also another sources of calcium) to your soil but limit your cultivation so you do not cause further drying of the soil.

For blossom drop your best best is too water your plants more consistently (poke finger in ground about 1 and half inch if dry water) and spray your plants with a seaweed extract and add organic mulch/compost to each plant to hold in more moisture.

Hey Sara... I grew habaneros in Sunnyvale and they did great.... then in Potrero Hill (which is sunny but cold) and they did awful. I doubt it's heat of the asphalt, I'd bet it's the cold. Peppers love the heat and lots of sun to ripen fully and it seems like habaneros need more of both then other peppers.