Mulch is one of the best things you can do to help your garden thrive.
Neatly mulched beds and pathways improve the appearance of any landscape. But, beyond its appearance, a layer of mulch provides many other benefits. It protects plants´ root systems and can add nutrients to the soil. It also slows the erosion of topsoil.
What are mulches? As stated in the California Master Gardener Handbook, mulches are materials put on top of the soil around trees and shrubs to reduce water evaporation, prevent weed problems and buffer soil temperatures. (To prevent stems and bark from rotting, pull mulch away from woody stems and tree trunks at least two to four inches. Before mulching, the area needs to be weed free.) Mulch can be organic or inorganic. Inorganic mulches are man-made materials such as recycled rubber and sheets of black or clear plastic, among others. I prefer organic mulches because they are derived from natural sources that enrich the soil through decomposition. I will limit my discussion to organic mulches because of space limitations.
Compost is one of the best mulches for providing benefits to the home garden. It is usually free of weed seeds and can be prepared from materials present on your property and from kitchen waste. It is not necessary to purchase expensive materials for mulching. However, I did purchase some commercial compost once and found it to be of little value to the soil.
Lawn Clippings are another source of organic mulch. Let them dry before using—to prevent clumping and matting—and then spread them thinly. Do not use clippings from a lawn that has been treated with herbicide. Untreated clippings make a fine addition to your compost pile and, because they are rich in nitrogen, they make good mulch for your vegetable garden.
Leaves are one of my favorite mulches and, of course, are plentiful in our foothill communities. In my garden they stay on the ground until spring, where they discourage weed growth and I like their appearance. Then I rake them up and relocate them to continue decomposing. Some composting instructions recommend chopping leaves into finer pieces before using them as mulch.
Pine Needles may also be used as mulch. They are a pleasant smelling, good-looking mulch that breaks down slowly. You may leave them in place for a season before removing to a compost pile or simply add another layer on top of the old batch. Pine needles may also be purchased in bales like straw. In fact, in the southeast, pine needles are used exclusively as mulch and erosion control and are referred to as pine straw.
Sawdust may be available to some of you. Let it age one year if possible. Fresh sawdust can temporarily deplete soil nitrogen if mixed into the soil. However, sawdust on top of the soil does not deprive the soil of nitrogen. Sawdust from plywood should never be used—the laminate glues holding the plywood layers together may be toxic.
Wood Chips, Shavings and Bark may also be used as mulch, but bark is expensive.
Straw is another choice. However, it is lightweight and tends to blow around. It decomposes quickly and therefore needs replacing more often than other mulches. My daughter in Colorado used straw on muddy clay soil as she planned and laid out what would become her lovely garden. I watched this process over several seasons and would recommend it to any gardener who must contend with such soil.
Newspaper or Shredded Paper is readily available and decomposes quickly. It may be used as mulch or added to compost piles. Colored ink breaks down slowly, may contain heavy metals and is not good for plants, so don´t use the colored comics or slick magazine or advertising pages.
When should we mulch? I found conflicting advice as I researched this subject. For example, Fine Garden Magazine states that because mulches´ main purposes are to cool the soil, suppress weeds and retain soil moisture, mulch is best applied in early summer. Applications made too early in spring delay root expansion of newly planted perennials and annuals. The Master Gardener Handbook tells us mulches should be applied in late spring when soils are warm. Three to four inches of mulch is usually adequate. Another source tells us to mulch evergreen perennials and ground cover in winter. Applied in late fall, winter mulch insulates plant roots. Proper mulching in summer months keeps the soil cooler and helps to retain moisture.
Mulching allows us to recycle nature´s products to replenish our gardens so that nothing is wasted.
Nina Bynum has been a Tuolumne County Master Gardener for eleven years. Each year she has become more of an advocate of using our native plants in her garden.