literally: to harvest the crops whilst it is still green; to leave the table as soon as one has made enough winning before having the chance to make some loss, typically in mahjong or gambling games [colloquial]
"plucking the greens", during the lion dance to celebrate Chinese New Year or the opening of new shops, auspicious green vegetable such as a lettuce (due to it sounding similar to "making money") is normally hung on a pole for the lion to eat