Home Gardening Tip Sheet: Compost and Mulch

By Sonia Uyterhoeven

·· Soil & Compost ··


Compost and Mulch in the Home Garden

One of the latest trends in gardening (although not new) is the idea that 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 plants. 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 particles 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 microorganisms 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 area or areas that are more ornamental, it is important to remember to repeat 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 and shrubs, annuals and perennials, or vegetables), and how intensively you are gardening. It will also be influenced by your soil conditions and your microclimate.

Adding Compost and Mulch to Your Garden


Adding compost to your garden will benefit the soil. You simply need to add between 1/2 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 to 15 inches. Compost can be added at anytime; normally it is added in the spring and often repeated in the fall after garden cleanup.

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.

Mulches suppress weeds, add organic material, and reduce the evaporation of moisture from the soil. Before mulching an area, add a layer of leaf litter or compost 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 a 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. Vegetables gardens can be mulched with straw, newspaper, and grass clippings while perennial gardens do well with shredded leaves and fine bark mulches.

Remember that soil compaction prevents healthy 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.

Do not garden too early in the season when the ground is supersaturated from winter rain/snow. Likewise, avoid gardening after a heavy rain--you will only compact the soil and cause more harm than good.

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. Since it destroys the soil structure and creates 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.

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Generous support for the Home Gardening Center has been provided by Kenneth and Ellen Roman.