Muffle bustling street noise with plants, water or walls

If you live near a major thoroughfare, you might have noticed how the decibel levels have increased in recent years.

A buffer of mixed plants can absorb and deflect sound waves. The mix of plants is important because different types of leaves reduce different types of noises. How much noise control they provide depends on the intensity, frequency and direction of the sound, and the location, height, width and density of the planting.

Mixed broadleaf plantings at least 25 feet thick and conifers 50 to 100 feet thick can drop noise levels by up to 10 decibels. For year-round noise reduction, plant a mix of evergreens such as arborvitaes, spruces, pines and hollies. To be effective sound barriers, these trees' foliage must reach to the ground.

Deciduous plants also are effective for noise abatement, but only when foliage is present. Like evergreens, these also must have foliage from the ground up to really do the job.

Include lawn or other ground cover in shady areas. Turf grass or other low vegetation has a muffling effect on sound, compared with surface areas of bare soil or various paving materials, which are more likely to bounce sounds off their surfaces.

But noticing noise might be as much psychological as physical. When you don't see the source of the sound, there's an implied screening that makes it less apparent. So the use of plantings between you and the noise at any width is valuable for most home landscapes.

Mask the sound

That's also a good reason to install something to try to camouflage noise. A fountain, music and screening might further contribute to a quieter yard.

Flowing water can be a wonderful foil for noise, especially if it has a cascading flow and makes a splashing sound. There are free-standing, tiered water features that offer some degree of noise screening.

Music in the garden can have a profoundly soothing effect on your surroundings and make the world around you seem to fade away. Some weatherproof speakers specially designed to be used outdoors have a very good sound quality.

Build a barrier

The most effective measures depend more on the configuration of the soil than the tree or shrub you're putting into it.

The best way to reduce noise is to establish a soil berm for your plantings: Large mounds of soil thickly planted do a much better job of blocking sound than plants alone. Make your berm as high as possible.

You also can effectively dampen noise for a small townhouse or postage-stamp-sized property with a fence or wall. Install a fence or wall with no openings that is tall and dense enough to shield outside clamor.

Be sure to check local codes and permit requirements before proceeding.

Joel M. Lerner is president of Environmental Design in Capitol View Park, Md., and author of "Anyone Can Landscape" (Ball 2001). Contact him through his Web site, www.gardenlerner.com.