# Noise Barrier Plants
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Solid Noise Barriers vs. Plants
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Plants don't affect noise levels detectably. Field studies found there is no difference in decibel levels behind a wide barrier of plants in summer or winter. Solid noise barriers don't block noise completely, but can reduce it by five to 10 decibels. This can mean the difference between the noise of a tractor-trailer and that of an automobile. The noise barrier has to be rigid and dense to achieve this reduction, weighing about 4.1 lbs. per square foot. Earth berms fit this specification, along with concrete, masonry block, brick, wood, and metal.
Plants and Aesthetics
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Your perception of noise reduction in part is related to non-acoustical factors. Aesthetics have an impact; noise barriers are judged as ineffective when people don't like looking at them. This makes visual quality a significant issue in noise barrier design, and plants have strong aesthetic benefits. The California Department of Transportation (Caltrans) likes to integrate plants with noise barriers, because they also obstruct vandalism -- especially graffiti -- reduce life-cycle improvement costs and construction costs, and help gain community acceptance.
Plants and Berms
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Earth berms are solid noise barriers that fit into the landscape. An earth berm is the most important component of a planted noise barrier, as it is effectively a solid wall. Mixed plantings of broadleaf shrubs and evergreen trees with foliage extending to the ground can absorb and deflect sound, but not as reliably as a solid barrier. Sound is muffled where ground covers, such as turf grass, are used, whereas sound will bounce off paved surfaces.
Noise Barriers at Home
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Planting to screen the source of the noise has psychological value; the sound will be perceived as more distant. The types of plants are not as important as the way they're combined with other features. In a residential landscape, a mix of dense plantings, berms, fences and solid walls can be combined to shield the environment from intrusive noise. These small measures will improve the quality of your own acoustic surroundings.
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