Peat moss is often recommended as an amendment for all types of soil. Clay is one of the most difficult soil textures to work with, requiring more space between the grains of soil to allow air and water to move through quickly. The combination of peat and clay can be beneficial for many plants but understanding the unique properties of each one will allow you to make the choices that benefit your plants the most.
The particles that make up clay soil are flat, like tiny plates. Like plates, they stack easily, leaving little space between them for the air that roots need. They give soil a sticky, dense texture that requires delicate handling. Too much digging while it's wet or too much standing on the beds will compress it and further reduce the air spaces. Clay holds moisture and nutrients well, but is difficult to wet once dried. The recommended remedy for an excess of clay in the soil is organic matter. Not only do organics hold water and nutrients like a sponge, they decay into a sticky substance called humus that will bind clay particles together into sand-like grains, leaving more space in the soil.
Peat moss is the decayed or partially decayed remains of a sphagnum moss that grows at the top of bogs with high acidity. As the bogs age, the layers of dead moss become deeper, finally leaving dense, brown peat and little else. Most peat moss sold now comes from northern Europe and Canada and is often the partially decayed remains of sphagnum moss rather than the dense blocks that were burned as fuel several hundred years ago. Peat is acid and very low in nutrients. For shipping, it is thoroughly dried and may be difficult to wet before using. A bit of dish soap added to water will help, as will using hot water rather than cold.
Mixing Into Soil
Spread a 2-inch layer of moistened peat moss over the ground you wish to improve. Do not mix when the soil is wet. Wait until it has dried to the touch through the top half inch. Mix the peat with the top layer of soil to 12 inches. Be careful to avoid stepping on the newly turned ground if possible.
Since peat is acidic, it is an excellent amendment if you wish to grow blueberries, rhododendrons, azaleas or other acid-loving plants. If planting a vegetable garden, add ground limestone to raise the pH to nearly neutral. Most vegetables prefer a slightly acid to neutral soil, 6.5 to 7.0. Potatoes are an exception, preferring a pH below 6.0.
Peat moss decays slowly, taking several years to transform to humus, while compost may be gone in less than a year. The humus binds the clay particles, but the fiber that loosened the soil and supported more air spaces is gone. Keep adding more organic matter each year, constantly renewing the fibrous texture of the soil.