If the smell of fresh mulch is in the air, it must be early spring in Greater Columbus. As soon the snow melts and the first warm sunny day appears, gardeners head for their local garden center where they find pallets of bagged mulches and two-story high piles of bulk mulches ready to be loaded and taken home to be spread on flower and landscape beds as well as around trees and shrubs throughout the home landscape.
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There are several benefits to applying mulch around trees, shrubs, annual and perennial flowers, and even vegetable gardens, with weed suppression likely being the primary objective for many gardeners. In addition to weed control, mulches help to retain soil moisture, moderate soil temperatures, prevent soil erosion and provide organic matter to the soil.
Gardeners have many options when selecting mulches to use in the garden and the home landscape. Organic mulches decompose over time and add organic matter to the soil as they decompose. These types of mulches may need to be refreshed each year. Synthetic mulches may not need to be refreshed each year but they do not add organic matter to the soil. Synthetic mulches may compact the soil and reduce microbial and earthworm activity required for healthy soil biology.
Let’s take a look at the variety of mulches available to gardeners.
Shredded bark, bark chips, pine needles, compost, rice hulls, various nutshells, shredded leaves, straw, hay and cardboard are all organic mulches. Biodegradable plastic sheeting is also available but it may take up to three years for this plastic sheeting to completely decompose and during that time, the remaining pieces of sheeting may be visible in the garden.
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Living mulches offer an outstanding opportunity for gardeners to build soil health below the ground and enhance design aesthetics above the soil. Plants such as crimson clover, borage, yarrow, lemon balm, and even kale can be used to create pollinator-friendly living mulches. As these plants grow, their leaves shade the soil and their roots create air and water pockets, necessary elements for good plant health. These living plants will also be attractive and hospitable to songbirds, butterflies, bees and other pollinators.
Rocks, gravel, plastic sheeting and woven landscape fabric are examples of synthetic mulches. Plastic sheeting and woven landscape fabric can be installed directly on the soil and covered with an organic mulch for aesthetic reasons.
Plastic sheeting and woven landscape fabric create impermeable and semi-permeable (respectively) barriers. These barriers prevent worms, water, and soil microbes from freely traveling throughout the soil. Limiting this movement interferes with normal biological soil activity.
Over time, these barriers can increase soil compaction and form a secondary barrier of living roots above and below the inorganic barrier itself. Rocks and gravel absorb heat during warm days and can transfer the heat to the soil. This increase in soil temperature and reduced soil moisture may also harm beneficial insects and microbes living in the soil.
Synthetic mulches are often more expensive than organic mulches but they generally have a longer life span than organic mulches and do not need to be replaced as frequently.
Mulches in a vegetable garden provide the added benefit of keeping the plants and edible plant parts such as tomatoes, squashes and peppers free of dirt and mud.
Most vegetable gardeners typically opt for inexpensive mulch options instead of bagged mulches. Straw is an excellent mulch that provides the added benefit of adding organic matter to the soil as it decomposes. Unfortunately, straw prices have recently escalated quicker than a gallon of gasoline!
Compost, dry leaves, dried grass clippings and even newspaper and cardboard are excellent mulches in the vegetable garden, although paper and cardboard require some management to keep them from littering your neighbor’s lawn in a windstorm. Keeping these mulches wet and covering them with a thin layer of compost or soil usually keeps them in place.
Synthetic mulches such as black plastic over the planting rows and permeable landscape fabric between the rows are excellent synthetic sources of mulch in the vegetable garden, and can raise the early spring soil temperatures by 10 to 12 degrees, allowing you to get an earlier start with both cool-season and warm-season crops.
Whichever type of mulch you choose be sure that, you only apply to a depth of no more than 2 or 3 inches. When refreshing existing mulch beds this may require removal a portion of the top layer of the existing mulch. Applying mulch deeper than 3 inches can damage the bark of trees and shrubs covered by mulch, interfere with moisture and oxygen infiltration, and cause roots to grow up into the mulch instead of deep in the soil.
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