What are the seasonal foods?

People in the south of the Yangtze River have a family reunion dinner when they are in Tomb-Sweeping Day. Green balls are made by mashing a plant called wheat straw with a tool, squeezing out the juice, and kneading the juice into a ball with glutinous rice flour, so that the green skin of the green ball is ready, the middle is wrapped with stuffing made of red bean paste, then steamed in a steamer, and the surface is coated with a layer of vegetable oil after taking out the pot, so that the green ball is ready.