Heavy soils are those with a large component of clay in them, because the clay particles bind together to form a heavy, sticky lump which is difficult to dig. Because it is composed of so many fine particles which stick together easily, it is liable to compaction. It holds a lot of water and easily becomes waterlogged, so it is cold and wet in spring, and takes a long time to warm up.

Clay soils are usually acidic

Heavy clay soils can be improved by adding humus or other organic matter and sharp sand for better drainage

Lime works best when it is mixed with the soil so it can come in contact with a large volume of the soil water. Since lime is not very soluble, it moves into the soil very slowly when applied to the soil surface

A little too much can raise pH to undesirable levels and keep it there, causing serious management problems. Make certain you know how much lime is needed, then apply it over a number of seasons until your soil is back in balance.