Flower drop probable causes:
1. Day temp too high >95F
2. Night temp too low <65F
3. Too much nitrogen fertilizer
4. Too much water
5. Low light levels (reduces fertility).
6. Very low humidity (reduces fertility)
7. Poor air circulation (air circulation contributes to pollination).
8. Lack of pollinating insects.
9. Size of pot
10. Too much mineral in feedwater.
11. Too much grower attention/anxiety.