Why is overseeding a hail cloud usually considered impractical?

Overseeding a hail cloud is generally considered impractical because it requires an excessively large quantity of seeding material to cover the necessary area to achieve an appreciable effect.1

In the context of meteorology, overseeding involves introducing so many nuclei into the supercooled regions of a cumulonimbus cloud that the water content is almost entirely converted into ice crystals. Because of the vast scale of these storm systems, the logistical and material requirements to perform this procedure effectively across a sufficient area are prohibitive.1

Instead of attempting to convert the entire cloud, most hail-suppression efforts focus on reducing the size of hailstones. By introducing a controlled amount of ice-nuclei seeding, meteorologists aim to increase the number of hailstones competing for the same available supercooled water. This results in a larger number of smaller stones that are more likely to melt into rain or reach the ground at a size too small to cause significant damage to agriculture.1