A soil amendment is any material added to a soil to improve its structure which can aid in water retention, permeability, drainage, aeration. The goal in adding soil amendments is to provide a better environment for roots.To be effective, an amendment must be thoroughly mixed into the soil.
Amending soil is not the same thing as mulching. Mulch is left on the soil surface to reduce water evaporation and runoff, reduce weed growth, and add an attractive appearance to the garden. Organic mulches may be incorporated into the soil as amendments after they have decomposed to the point that they no longer serve their purpose.
Organic amendments come from something that was alive, such as wood, straw, sawdust, peat, and grass clippings. Inorganic amendments are man-made.
Organic amendments increase soil organic matter content and offer many benefits. Many organic amendments contain plant nutrients and act as organic fertilizers. Organic matter also is an important energy source for bacteria, fungi and earthworms that live in the soil.
Fresh manure can harm or kill plants due to high ammonia levels. To avoid this, use only aged or composted manure. Aged manure is manure that has been piled for at least six months.
Compost made solely from plant-based products such as wood chips and yard clippings are low in salts. Be sure to compost wood chips and sawdust, before using as soil amendments as it is slow to break down and ties up nitrogen the plants need.
Sphagnum peat is an excellent soil amendment, especially for sandy soils, which will retain more water after adding sphagnum peat to the soil. Since it is acidic it can help gardeners grow acid loving plants such as blueberries and hydrangeas.
When amending sandy soils, the goal is to increase the soil’s ability to hold moisture and store nutrients. For this to happen, use organic amendments that are well decomposed, like composts, peat, or aged manures.
With clay soils, the gardener is looking to improve soil aggregation, increase porosity and improve aeration and drainage. Choosing soil amendments like peat, wood chips, tree bark or straw are the types to choose from.