Happy St. Patrick’s Day!
The shamrock legend can be traced to the 5th century saint who used a three-leaved plant—possibly white clover (Trifolium repens)—to demonstrate the concept of the Christian trinity. Today, oxalis cultivars, or any plants with tripartite leaves labeled as shamrocks, are sold as houseplants or outdoor plants.
Our Pacific Northwest native Oxalis—sometimes called wood sorrel—is a beautiful ground cover for mostly shady areas (but also more open, shrubby areas) at low to middle elevations. It has edible leaves high in oxalic acid (like spinach), and forms a lush carpet in moist to dry woodlands.
Three wood sorrel species that occur naturally in the region are Oxalis oregana (wood sorrel or Oregon oxalis), O. suksdorfii (western yellow oxalis, which occurs mainly in southwestern WA and Oregon at low elevations), and O. trilliifolia (trillium-leaved oxalis). When deciding which species to grow, pick one that naturally occurs in your area (see map links in previous sentence).
Oxalis is a pollinator plant, offering its charming small flowers to native bees, syrphid flies, and butterflies. Like most flowering plants that grow under low light conditions, its blossoms are white or light colored to enable pollinators to be able to easily see them. Later in the year, Oxalis seeds may be eaten by seed-eaters like sparrows and small rodents. Its leaves serve to protect and enrich the soil.
Try it at home
Grow it in the shade of tall trees like Douglas fir and with other native woodland species such as Vaccinium spp. (huckleberry), Mahonia nervosa (Cascade Oregon grape), Gautheria shallon (salal), Polystichum munitum (sword fern), Prosartes spp. (fairy bells), Trillium ovatum (western trillium), and others.
Give it moist, acidic soil (pH 5 to 6.5), preferably rich in organic matter. While morning sun is welcome, it typically won’t do well with scorching midday or afternoon sun. In full shade and once established, it is a drought tolerant plant. Be sure you like it, though, because it will spread—enthusiastically, in the right conditions—to protect the soil and soil dwellers.