There are a variety of reasons gardeners apply mulch. One of the main reasons is aesthetics – a mulched garden looks tidier and more attractive.
In addition to how it looks, mulch also provides a number of services to the garden and is an important part of maintaining plant health in a comprehensive Integrated Pest Management program.
As any gardener knows, weeds are a constant problem in the landscape. A layer of mulch prevents weed growth by smothering small weed seedlings. Also, mulch prevents air-borne seeds from taking hold in the soil. It also protects plants from soil-borne diseases by preventing rainfall and irrigation water from splashing pathogens onto the plants.
Not only does mulch protect the plants, but also it protects the soil by reducing soil compaction and erosion caused by foot traffic, wind and rain.
In addition, mulch helps regulate soil temperature by shading it in the summer and providing insulation in the winter. This temperature regulating effect helps encourage root growth of plants.
Mulch also reduces moisture loss from the soil by preventing evaporation from sunshine and the mighty wind we’re all familiar with here in Oklahoma.
Garden plants aren’t the only vegetation to be enhanced by mulch. It can help prevent damage to trees and bushes by protecting their stems and surface roots from garden tools such as weed eaters, edgers and lawn mowers.
Finally, mulch provides a home for earthworms and natural enemies found in the soil. Insects, spiders and centipedes seek shelter beneath litter on the soil surface.
Mulch provides ample places for these arthropods to hide during the day. These predators will feed on a variety of garden pests during the cooler night hours. To see evidence of this, simply lift a rock or move aside the mulch in your garden and you are likely to see a ground beetle scurry away.
Mulch can be broken into two main categories: organic mulches, which are derived from natural materials, and inorganic mulches, composed from synthetic or man-made materials, mainly plastic or aluminum.
Organic mulches are by far the most common in an ornamental garden. These include cut grasses, leaves, straw, hay, wood chips, bark, animal manures, plant debris or newspapers. Organic mulches decompose over time, adding organic matter to the soil and improving soil conditions. Organic matter loosens soils, which improves the root growth, increases water absorption and also improves the soil water-holding capacity. Decomposed mulch contributes nutrients to the soil that can be utilized by plants.
Inorganic mulches include plastic and aluminum foil. These aren’t typically used in a home landscape, but can be beneficial in the vegetable garden. Different colored mulches are used to control a variety of pests. Aluminum mulch reflects sunlight and confuses and repels flying insects from coming onto the plants. Studies show red plastic mulch repels root maggots and other flies, while blue mulch confuses winged aphids and thrips. Black plastic mulch discourages sowbugs and other crawling pests that can’t withstand the heat and also helps in managing leafminers. Keep in mind, however, the pests from different regions react differently to various colors.
Kimberly Toscano is assistant extension specialist and host of the OETA television program Oklahoma Gardening, which airs at 11 a.m. Saturdays and 3:30 p.m. Sundays, and assistant director of The Botanic Garden at Oklahoma State University.