Pea gravel, tiny stones that are 3/8-inch in diameter, is incorporated into clay soil to provide drainage and ease compaction. Pea gravel alone, however, will not benefit plants and flowers because it provides no nutrients or organic matter.
Pea Gravel Benefits
Sticky and dense, clay soil is composed of small mineral particles that stack up against one another. Water and air cannot circulate through densely stacked particles. As a result, clay soils are often saturated and pool water. To facilitate drainage, pea gravel is incorporated into soil to break up the stacks and provide water and air a chance to circulate. Sharp stones also discourage tunnelling vermin from infiltrating the garden.
Pea Gravel Drawbacks
Because clay soil is prone to compaction, working clay soils is not recommended. Problems increase when soil is stepped on and dug up. Unfortunately, to incorporate pea gravel, soil must be dug up and gravel worked into it. This is an acceptable solution to drainage problems in areas such as driveways and open space. It is not recommended for gardens. If you are planting a garden, consider pea gravel alternatives.
Compost is regarded as one of the better clay soil amendments. No-till methods are used to incorporate compost into soil without causing damage. Instead of disturbing soil with a shovel, cover crops are grown and used as green manure. After the crops die, they are gradually incorporated into the soil.