The Passionate Gardener: In Praise of Mulch

Ron Kushner, for the Shuttle

Just about the best thing you can do to any garden is cover it with mulch.

By mulching, you are suppressing weeds by blocking their access to light and air, retaining moisture by slowing down soil-surface evaporation and adding organic matter, which improves the soil as it decomposes. Mulch also tends to keep the plants cleaner and free of disease because it prevents many fungal spores from bouncing up onto the leaves as you water or when it rains.

Organic mulches include materials that used to be living, such as shredded leaves, straw, grass clippings, compost, sawdust and pine needles. Inorganic mulches include landscape fabric, plastic and stones and gravel. While inorganic mulches also discourage weeds, they do not decompose and enrich the soil, but they do tend to warm the soil faster in the spring.

Organic mulches must be thick enough to discourage weeds from pushing through — usually 4 to 6 inches. Shredded leaves make a good organic mulch and the price is generally right. While the leaves themselves are usually free, you may want to invest in a shredder. There are many on the market. For home gardeners, a good one to look for is an electric model that fits on a standard trash can. Leaves are raked into a funnel-shaped hopper. The grindings come out of the bottom, fill the trash can and are ready to use immediately.

If your garden was mulched over the winter, pull the mulch away from existing plants and bulbs so the soil gets a chance to warm up. The mulch can be reinstalled later, when the plants are actively growing. Keep mulch at least 1 inch away from stems and crowns, as wet mulch can lead to rot.

As mentioned earlier, mulch acts as a barrier to fungi and bacteria in the ground, keeping them from splashing onto the leaves and causing disease. And as it is decomposing, mulch provides a perfect environment for beneficial insects.

If there are parts of your yard where you don’t use mulch, at least make sure there is no bare soil, which will lose humus and nutrients and, especially if tilled, risk having its structure totally destroyed by rain. Install ground covers or additional plants.

Living mulch

Cover crops or “green manures” planted between rows and plants also keep weeds down and add organic matter to the soil. Green manure consists of plants that are eventually incorporated into the soil, increasing organic matter and fertility. Plants such as sweet alyssum, soybeans and clover provide the same benefits as traditional mulches but are actually a growing crop. Not only is there an aesthetic quality to a living mulch, but pollinators and other beneficial insects are attracted to them during the growing season.

Mulch for vegetables

Straw is a collection of stems of field crops such as wheat and oats left over after harvest. It is popular as a mulch because it is inexpensive and readily available but it does contain seeds.

Salt hay, also known as salt marsh hay, consists of grasses harvested from salt marshes on the East Coast of the United States. The wiry stems do not mat down or rot as quickly as straw and any seeds are unlikely to germinate because they require wet, saline soil. In colonial times, it was used for both animal fodder and bedding as well as mulch for gardens; it was harvested using draft horses as late as the 1930s. Salt hay makes excellent mulch, as it can last several seasons. It must be 3 to 6 inches thick to be effective.

Hay is the term used for a wide variety of grasses used for animal feed and as such, usually includes plenty of seeds. So it is better suited for feeding livestock than for mulching your garden.

Chopped and shredded hay and straw comes in a 3.5-cubic-foot plastic wrapped bale weighing about 25 pounds. It is easy to spread and easy to store. It is processed in a factory where it is chopped into short pieces and seed heads removed. One bale can cover up to 800 square feet but you should apply it extra-thick under vegetable plants. It is especially useful around small seedlings, which are difficult to mulch with coarser materials.

Wood chips, bark or hardwood mulches are not preferable or even suitable for use in vegetable gardens. They tend to use up the nitrogen in the soil for their own decomposition at a faster rate and provide an environment for fungus that isn’t desirable around vegetables.

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