Potassium has an important role in determining fruit quality and size. It increases berry size and evenness in the bunch.
The concentration of calcium within the berries decreases during ripening. This is due to the majority of the calcium is located in the skin of the grape. It is very important to maintain the level of this calcium by using applications to the vine throughout the season and/or sprays targeted at the fruit.
Iron can increase total grape yield and berry size and shape. Lack of iron reduces leaf growth and resultant berry size.