Why does organic matter improve soil more than sand, topsoil or any other amendment? If you have a heavy soil that is hard to work, the organic matter makes air pores so water can flow easily into and through the soil. As microorganisms and worms use the organic matter for food, they produce sticky, gluelike compounds that aggregate clay soil into larger particles up to pea size. If you have sandy soil, organic matter has the ability to hold water and slow down its movement through the soil. Organic matter also holds onto nutrients so they can be absorbed by plant roots before they leach below the root zone.
Fall is also a good time to add lime to the lawn and landscape. Soil and water in Western Washington and Oregon are acidic. Lime reduces acidity and makes most plants grow better. Lime can be incorporated into the soil when adding organic matter. It can also be applied to permanent plants such as trees, shrubs and perennial flowers. I like to cultivate lightly around permanent plants to get the lime mixed into the top surface of the soil. Do not add lime to soil around acid-loving plants such as rhododendrons, azaleas and blueberries.
You can apply up to 5 pounds of lime per 100 square feet. I like to add a pound or two every year. I always mix lime into the soil around all newly planted plants.