Washington County, OR Invasive Plant Rules: Prohibited Species (2026)

Section 407-2, Standards for Landscaping Materials, governs every planting installed to satisfy the code's minimum landscape requirements under Section 407-1, whether for a residential yard, a commercial parking lot or a required screening buffer. 2 lists three categories of prohibited plant material. A, plants with root structures the Director identifies as likely to damage or interfere with underground electrical lines, cables, conduits, pipes, sidewalks, curbs, gutters, paved parking areas, drainage improvements, or adjacent structures and foundations are barred. on December 21, onto an existing solar collector, protecting a neighbor's rooftop solar investment from being shaded out by new landscaping.

C prohibits any plant identified on regional or local plant lists as invasive or noxious plant species, which pulls in state noxious weed lists and regional invasive-species inventories rather than creating the county's own separate list. 3 layers on a companion design standard: landscape materials should be selected and sited to produce a hardy and drought-resistant landscaped area, considering soil type, exposure, slope and compatibility with existing native vegetation already preserved on the site. Because these are development-approval standards rather than a general nuisance ordinance, they apply at the point a landscape plan is submitted under Section 407-4, not retroactively to plants already established on a lot before development review.