Contrary to popular thought, plants DO NOT provide an effective noise barrier unless the planting is very deep and consisting of multiple layers - hardly something that can be easily accomplished in most suburban gardens. Not knowing exactly how much space is available along the property line, you could perhaps attempt such a layering, but I'd still be doubtful about its effectiveness to block much road noise. And unless you focus on evergreen natives, there will be no effect in winter. Most of the native broadleaved evergreens need a fair amount of sun, but you could consider mahonia, Pacific wax myrtle, Rhododendron macrophyllum, evergreen huckleberry and garrya for a lightly shaded situation.

A fence would be much more effective.

A row or two of dense evergreen trees will block the view and maybe some of the dust, but you won't get much noise reduction. Blocking noise is very, very difficult. The masonry walls that are built between houses and highways work pretty well if they are done right. But they are expensive. I have had two recent experiences trying to solve this problem, with very limited success.

West coast newcomers may not notice most here are using USDA zones or even know about USDA system, post using Sunset zones. Sunset 5 starts north of Seattle area and goes down coast into California, so many people live within its coverage.

For all practical purposes plantings do not block noise. Take a walk in the woods, that goes near a highway part of the time and you will see how the roar of it penetrates the forest so well that it sounds closer than it actually is.

Correction--our property is on the east side of the road. Sounds like my idea of using plants and trees might not work out. We are in a rural setting all wooded with houses on 5 acre tracts. We are leaving about 80 feet of space natural between our house and the road. Would this be enough space to layer plants and trees? Besides the firs there now is mostly salal, huckleberry and lots of moss and old downed trees. None of these plants are dense. I think we are in zone 5. We live north of Lacey about 3 miles from the sound. There is not steady traffic along the road just the occational sound of a car going 50 to 60mph. Thank you for your input!

You are in Sunset zone 5, USDA zone 8. 80' may be deep enough to effect a good layering, however how much this will effectively block road noise is a bit of a toss-up. My guess is not much.

Native understory plants (those that commonly grow under the canopies of native conifers) will not be dense - that's just their nature. Restricting yourself entirely to natives may be unnecessarily limiting. You might want to consider another layer or hedged area closer to the house using more ornamental species and incorporating a small water feature - the white noise of moving/splashing water is a great foil against other, less desirable sounds.

Even though they won't block noise, I'd give a vote for pacific wax myrtles. They're beautiful plants - evergreen with nice foliage for cut arrangements. I planted a few small ones ($6.95 or so from Molbak's) three years ago, and they're already about 10' tall.

Here is a link that might be useful: scroll down on link to see picture

I've never tried to block noise with plantings, and I'm surprised that it doesn't seem to work, but I'm grateful for the information.

As far as plant suggestions go, the first plant that came to my mind was Pacific wax myrtle as well. They really are nice evergreen plants that are quite dense. I've planted them in two Seattle gardens and after a season or two they were totally on auto-pilot and grew like weeds.

Let us know what you decide to do and how it works out.
Take care,
Grant

Full sun for Myrica californica, soon grows thin if shaded much. Also prone to weevils in proximity to taller evergreens, as are many other shrubs. Grows natively right behind beach on outer coast, at Ocean Shores development often mixed with Hooker willow -- underscoring preference for full light (and moist soil).

You might also consider plants as understory that aren't necessarily native, but with a breeze create white noise which will tend to drown out traffic noise. Pines and bamboos are very effective in this regard, and the rustling of leaves or sighing of boughs is more pleasant than traffic noise. Denser growing hedge like shrubs such as Irish yew or English Laurel might also be worth checking into.

I hope you are using the slope to build a Solar home. Building into the slope would provide the most sound protection, and permanently lower heating and electricity costs. An atractive rock wall or stone berm facing the road could also provide an architectural sound barrier, natural fencing, and can absorb sun for selected plants. trees also look great with rock. Evergreens would be my choice if you aren't planning a food garden.

Fruit and nut trees, and a grape arbor are also options, as is a greenhouse to the southeast, between your house and the road? Enjoy your new place!

Plants don't do a good job of reducing noise. I think it's like 5-10% reduction in noise with dense plantings. Whereas dense objects like wooden fences or rock walls, concrete walls, do an excellent job at reflecting/reducing noise. 40-60% noise reduction with dense materials.

Thanks to all for your input on my question. I'm sure I'll be asking more as our project gets further underway. We worked out on the property yesterday afternoon--lots to do! You guys are great!