Plantings near the sea in Oregon and Washington often have special challenges to face: high winds, excessive rain, summer fog, sandy soil, drying sun and salt spray. Your best chance of success lies in using plants that have adapted to these conditions. You may think of the Northwest as rainy, but summers can bring dry spells of a month or more. Choose plants that thrive with little water whenever possible.
Use one or two ground covers throughout your yard to give a sense of unity to the planting. Not only will they conserve moisture and reduce the number of weeds, but they stabilize sandy soil.
Try four or five to start and choose the ones that grow the best in your garden, then plant them thickly. You can create sweeping curves and geometric shapes with just a ground cover and plastic lawn edging to give the shape definition.
Ground covers that thrive on the Northwest coast include common yarrow (Achillea millefolium)---a spreading, ferny perennial with heads of white flowers in summer that rise a foot and half above the foliage.
Lady's mantle (Alchemilla mollis) has large, soft, lobed leaves and sprays of greenish flowers in summer. It likes shade but also does well in full sun, growing up to a foot and half high and wide.
In the mild Northwest, you can use quite a few perennials in masses to give a sense of structure to your garden. Five or six of the popular Sedum "Autumn Joy" are attractive, but 20 of the plants become eye catching. The key lies in trying a few of five or 10 possibilities and finding those that grow best under the unique conditions of your garden. Then plant as many as you can.
Daylilies are tough, easy-to-grow plants with flowers in many shades and sizes. They spread slowly to form large clumps, and their strap-shaped leaves provide a nice texture contrast to ferny yarrow and round-leaved lady's mantle. Some are nearly evergreen in western Oregon and Washington.
For shade, try hellebores. Their purple, pink and white flowers in spring are lovely, but their large shiny leaves are an asset year around. They are drought-tolerant and easy to grow.
You can use large shrubs to give shelter from the wind, and small ones in groups to add height to massed plantings. Rosemary often occurs as single specimens, but groups are effective as a background for lavender and sage---both useful seaside plants. Use the hardiest varieties of rosemary in the colder areas of Washington.
Rugosa roses, also called beach roses, spread by underground runners to form large clumps, best in the background. The usual color is a purple-pink, but varieties are available with clear pink, white and double blossoms. They have the advantage of cast-iron hardiness and salt tolerance.
Pacific wax myrtle (Myrica californica) is a large evergreen shrub that makes a good, dense windbreak but may also be trained as a small tree. It has no flowers, but the long pointed glossy leaves are attractive on their own.
Shore pine, as its name indicates, is an excellent choice for Northwest coastal areas. A native of the windswept beaches, it is an attractive specimen tree and also works well in groups to give needed shelter from the wind.
If you want fall color, vine maple (Acer circinatum) is a good choice. Native to the lowlands and mountains of Oregon and Washington, it prefers shade but can take sun if given plenty of water. It grows into a small tree with roundish leaves and a picturesque shape that lends itself to planting in small groves.