Question

why are grapes sweet in March and April

Answer 1

"Grapes" are easy to find and usually available all through the year. However the incredible flavor of grapes is experienced only at certain times in the year. Grapes become sweeter and less acidic when they mature and this is one of the most important factor's. Grapes are harvested by March and April, by when they also attained their sweetness.  

Answer 2

Every fruit and vegetable are tasteful in their own seasons in which they actually grow. March and April are the seasons of the grapes and the color of the grapes in this season is Green, green grapes are the sweetest or if the grapes are rich in color they are the sweetest in taste.