Native Plants for Washington

Washington's Cascades create one of the most abrupt rain shadows in North America. West of the crest, moist Pacific air rises and drops enormous precipitation: the Olympic Peninsula includes temperate rainforest receiving among the highest rainfall totals in the contiguous states.

East of the crest, the same air arrives dry. The Columbia Basin is shrub-steppe, with sagebrush, bunchgrasses, and annual precipitation low enough to qualify as semi-arid. Parts of it receive under ten inches a year.

Two gardens a hundred miles apart, on either side of the mountains, share a state and essentially nothing else.

The dry summer applies on both sides

The one thing western and eastern Washington do share is a Mediterranean-leaning rainfall pattern: wet winters and a genuinely dry summer. Even in rainy Seattle, July and August are dry months, and gardeners regularly underestimate this because the annual total sounds so generous.

Native plants west of the mountains are adapted to that: they grow hard through the wet season and slow down in late summer. Species from summer-rainfall regions need irrigation here precisely when water is scarcest.

West side: acid soil and shade

Western Washington soils are generally acidic, and the forest flora suits them: salal, evergreen huckleberry, sword fern, Oregon grape, red-flowering currant, and vine maple. These are excellent garden plants and they handle the shade cast by conifers, which defeats most perennials.

Drainage varies widely, from gravelly glacial outwash on parts of the Puget lowland to heavy clay elsewhere. Read the site.

The Puget prairies, the remnant grasslands of the south Sound, are a rare and much-reduced habitat, and their species suit sunny, well-drained sites.

East side: steppe and sun

East of the Cascades the palette changes to shrub-steppe: big sagebrush, bitterbrush, bluebunch wheatgrass, Idaho fescue, lupines, balsamroot, and buckwheats. Soils are often alkaline, and summers are hot with cold winters.

These species want lean soil, full sun, and almost no summer water once established.

Timing

Fall planting suits both sides of the state, letting winter rain and snowmelt establish roots before the summer dry period. West of the mountains the autumn window is long; east of them, plant earlier in fall or in spring.

Water new plantings through their first summer, then reduce.

Confirming what is native to your county

The Washington Native Plant Society runs chapters on both sides of the Cascades, and the differences between their recommendations illustrate the split well. The Burke Museum at the University of Washington maintains the state's herbarium records and image collection, and Washington State University Extension publishes regional guidance.

Sources: Washington Native Plant Society (regional plant lists); Burke Museum, University of Washington (herbarium records and distribution); USDA PLANTS Database (native status by state).