Soil is a dynamic, living system that needs to be managed, not by pouring harmful chemicals and salts into it, but by supplying it with its nutritional and cultural needs.
Soil plays a critical role in the life of a plant. It anchors a plant, supplies nutrients, water and oxygen. Soil is an aggregate of sand, silt and clay. They have different properties, with the larger particles of sand providing good drainage while the fine particles of clay retain moisture.
Organic matter breaks down into humic acid, a black, gelatinous liquid that holds the soil particle together leaving spaces for water and oxygen. Organic matter improves drainage, soil aeration and enhances the soil's ability to hold nutrients.
Organic matter and soil are full of life. Bacterial and fungal micro-organisms cycle nutrients and make them available to plants. Larger soil organisms, such as earthworms, work the soil by providing nutrients through their excrement and create good drainage as they tunnel underneath the surface.
Compost acts like a steam engine that energizes and drives this dynamic system. Healthy soil means healthy plants; plants grown in fertile soil are less prone to pest and disease problems.
While compost is sometimes referred to as "black gold" because of all the benefits it provides, remember that all you are doing when you incorporate compost into your garden is repeating a process that nature does on her own. Composting is simply recycling organic material - breaking it down - and returning it to the environment.
This is important to remember when tending your garden. In naturalistic areas, leaving leaf litter to decay on its own is a healthy and natural way of composting. In highly cultivated areas or areas that are more ornamental, it is important to remember to replicate these processes by adding compost or by mulching.
The care of your garden will depend on your cultivation practices, how you are using the space, what you are growing (trees, shrubs, perennials, vegetables or annuals) and how intensively you are gardening. It will also be influenced by your soil conditions and your microclimate.
Adding compost to your garden will benefit the soil. You simply need to add between ½ inch to 1 inch of compost around your trees, shrubs, perennials, on your lawn, and in your annual and vegetable garden.
In an established garden, you can add the compost on top of the soil and let it seep in, or you can lightly fork it over. Once incorporated into the soil, it will improve the first 6 to15 inches. Compost can be added at any time; normally it is added in the spring and often repeated in the fall, after garden clean up. Compost cannot replace soil but should be used to amend it.
Shredded leaves are a cheap and easy way to add organic matter to your garden. They decompose quickly and add nutrients to the soil. Renting a leaf shredder or running your lawn mower over leaves are two good ways of shredding. Un-shredded leaves take longer to break down and, if too thick, can get matted into impenetrable clumps. Remember to be cautious when using a leaf shredder or any powered equipment. Dangling scarves and loose clothing should be avoided.
Mulch suppress weeds, adds organic material, and reduces the evaporation of moisture from the soil. Before mulching an area, add a layer of leaf litter to provide extra nutrients. The compost and leaf litter will be incorporated quickly, while the mulch will take longer to break down.
Add a maximum of 2 to 3 inches of mulch to your garden. A deeper layer could deprive the soil of oxygen and block moisture. Never pile mulch up at the base of the plant; it will just encourage rot and infection. The best time to apply mulch is once the soil has warmed in the spring and after a period of heavy rain.
Good mulches to use are shredded leaves, bark chips (shredded fine or coarse), pine needles, grass clippings (not too deep otherwise it will become anaerobic), and straw. Fine mulches will break down quickly into organic matter and coarse mulches will take a few years to decompose. Vegetable gardens can be mulched with straw, newspaper, and grass clippings combined with aged cow manure to create an ideal environment that is rich in organic matter. Perennial gardens do well with shredded leaves and fine, bark mulches.
(For a green material that is high in nitrogen, consider adding coffee grounds to your compost pile or directly to your garden. Check out the tab Coffee and Compost at the top of this page for more information.)
The advice varies slightly for planting trees. The soil that you plant a tree in should be similar to the soil in the surrounding area. If the soil is too rich, the roots of the tree will not grow past the nutrient-rich material used to fill the hole. Add compost if you are planting in heavy clay or sandy soil that has difficulty in holding nutrients. If you are amending the planting hole, try to amend as much of the area as possible. Add compost to the mulch as part of the top dressing.
Do not garden too early in the season when the ground is supersaturated from winter rain or snow. Likewise, avoid gardening after a heavy rain; you will compact the soil and cause more harm than good. Remember that soil compaction prevents heavy growth. It reduces the amount of oxygen available in the soil, prevents proper drainage and doesn't give the soil microbes the air and the space that they need to survive.
In cold climates, the natural process of freezing and thawing breaks up the compaction in the soil. Staying out of your beds, building raised beds, or creating paths are all good ways of avoiding compaction in your garden.
Traditionally, rototilling was a favored way of breaking up soil. But since tilling in excess can destroy the soil structure and create a hardpan, most people feel that the drawbacks outweigh the benefits. Forking over the soil is often a less invasive way to break compaction. Aerating your lawn every few years in the spring is also an important part of lawn maintenance.
Healthy Soils for Sustainable Gardens by 
Taylor's Weekend Gardening Guide to Soil and Composting by 
