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]
reaping the Poaceae when it is not ripe, meaning when one gambles, he / she should leave right away after winning some money, rather than staying and risking to lose
"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