Mulch is commonly used in landscapes and gardens because of the many benefits it provides to plants and soil. Fall is an especially good time to apply it. Gardeners often ask what materials are best for mulching and how much to use. The answers depend on how and where the mulch will be used, transportation, budget, and gardeners’ personal preferences.

The term mulch refers to material placed over the soil surface to protect soil and plants. Mulching is a way of recreating a natural environment. In forests, trees naturally mulch themselves by dropping leaves that break down and eventually are returned to the soil. Any mulch that is plant-based (sometimes called organic mulch) will break down and provide this benefit.

Organic mulches improve air and water movement through the soil, provide small amounts of nutrients for plants, and make other soil nutrients that are already present in the soil more available to plants.

Mulch can also provide other benefits, whether it’s an organic mulch or an inorganic material such as decorative rock.

Most importantly, all mulches reduce and prevent soil erosion. They also create a layer of insulation that reduces temperature and moisture fluctuations. A layer of mulch benefits microorganisms living in the soil in addition to plants growing in it.

Mulch can reduce weed growth by preventing light from reaching weed seeds on or close to the soil surface. It may also reduce the occurrence of fungal and bacterial plant diseases that spread by splashing, such as leaf spots on tomatoes.

A good time to apply

Fall is a good time to apply mulch to the garden to add an extra insulating layer for plant roots and reduce the amount of freezing and thawing of soil that occurs over the winter season.

Wood chips are the most popular mulch because they are readily available, easy to apply and last a fair amount of time. They work well as mulch around trees, in landscape beds and in bare areas where it may be difficult to grow plants, such as under an eave. Wood chips can be purchased in bulk or bagged. Bark mulches are similar to wood chips and provide the same benefits.

Bulk wood chips are available at a few local garden centers, from local arborists and from the City of Lawrence Compost Facility, which is open on Saturdays. Those who prefer wood chips that are ground to a more uniform size and texture or dyed a certain color can find these options at garden centers. For bulk wood chips, you’ll need a vehicle or trailer to haul them, or you’ll need a place in your yard for the garden center or arborist to dump a load of mulch.

Bagged wood chips are available at garden centers, hardware stores, box stores, grocery stores, etc. They are considerably more expensive than bulk wood chips, but they’re a great option for small gardens and for gardeners who do not have a place where bulk mulch can be dumped or a vehicle suitable for hauling bulk mulch. They are convenient and easy to handle, and a variety of colors and textures are available.

What type of wood the mulch is made from doesn’t matter much. Remember that mulch should fade into the background — the plants should be the focal point of the garden.

When applying wood chips or bark, use a 3- to 4-inch layer around most plants. More is OK as long as it is not piled against plants or covering the trunk or crown. You can also use less than 3 to 4 inches, but frequent reapplication will be necessary.

Straw and hay are another common material for mulch. These are preferable for vegetable gardens because they break down more quickly than wood chips and can be easily incorporated into the soil as needed when the time comes to plant the next crop. This is one mulch that may be best placed in the spring right after planting and left in place until the following spring. In the fall, additional straw or hay can also be placed over bare soil in the garden. Use enough to prevent sunlight from reaching the soil surface.

Shredded leaves, compost, grass clippings, and other plant materials can also be used as mulch. Leaves and grass clippings may develop an odor and be less aesthetically pleasing to some gardeners, but they still get the job done. Compost makes a great mulch, but it has to be reapplied often, as it quickly works its way into the soil surface.

Decorative rock or gravel is another option. It does not provide the soil improvement benefits of organic mulch, and it can be difficult to move if plants ever need to be replaced. However, it can be particularly effective in areas prone to erosion, gutter overflow and drainage. Use landscape fabric under the rock to keep it from disappearing into the soil over time.

— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation.