Gardening with Allen: Use leaves to help build soil quality

How can I use my falling leaves to improve my garden and landscape?

The best way to improve any soil is to add organic matter. What better time to do it than when we have lots of organic matter falling from trees. Leaves can be tilled into the vegetable garden and annual flower beds. The leftover vegetable and flower plants also make excellent organic matter. Till them in with the leaves.

Leaves make excellent mulch around trees, shrubs, berries and perennial flowers. You can run your rotary lawn mower over leaves to chop them into smaller pieces before using them as mulch. I add an inch or two of chopped leaves and grass clippings in the fall around all of my permanent plants.

Other good sources of organic matter include grass clippings, bark dust, sawdust, peat moss, coco fiber and various commercial composts that usually contain bark and manure. Manure, although usually thought of as a fertilizer, does as much good for physical soil improvement as for fertilization. Even fresh manure can be added in the fall without any worry about burning. Manure that has been stored near weedy areas can be a source for weed seeds. Bagged manure has been heat composted to kill weed seeds.

You can add as much as 3 to 4 inches of leaves, compost or bark dust when incorporating it into the soil. Or you can add a smaller amount and do it yearly for gradual improvement.

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.

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