Ming Qian (Pre-Ming) tea means teas plucked before Qing Ming. This year's Qing Ming is April 5, which means teas plucked after that can't be called Ming Qian tea. Yu Qian tea means teas plucked between Qing Ming and Gu Yu. This year's Gu Yu is April 20.
Green tea prices are generally very sensitive to these two days. Ming Qian tea normally demands hefty premiums. Yu Qian teas sometimes can be good bargains. After Gu Yu, it normally is game over for green tea producers with the exception of some northern region green teas, which harvest late due to cold weather. Although some companies produce teas all year long, quality of later harvest is nowhere close to that of spring harvest.