Seattle, WA Landscaping Rules: Native Plants (2026)

Where zoning requires a minimum Green Factor score, SMC 23.86.019.A directs the applicant to identify every proposed landscape element, sort it into the categories in Table A for 23.86.019, and multiply its square footage by that element's multiplier -- ranging from 0.1 for low ground cover up to 1.0 for bioretention facilities or preserved trees at least 6 inches in diameter at breast height. Subsection A.4 has the applicant divide the resulting Green Factor numerator by lot area to get the final score. Table A's bonus section, item G.1, adds a separate 0.1 multiplier specifically for "landscaping that consists entirely of drought-tolerant or native plant species," stacking on top of the base credit for the same planted area -- the code gives the example of groundcover under a tree being counted at full square footage for each element (subsection A.2.a).

Other bonuses in the same table reward landscaping irrigated at least 50 percent by harvested rainwater (0.2), landscaping visible from the right-of-way or public open space (0.2), and food cultivation (0.1), so a native-plant bed that is also visible from the street and rain-irrigated can stack multiple bonus multipliers. The Director sets the underlying planting standards -- plant type and size, spacing, soil depth and quality, use of drought-tolerant plants, and access to light and air -- under subsection A's opening sentence. Permeable paving and structural soil credits together are capped at one-third of a lot's total Green Factor score (subsection A.2.g), which keeps the native/drought-tolerant plant bonus meaningfully tied to actual planting rather than hardscape substitutes.

Elsewhere in Title 23, the code ties Green Factor scores to other approvals: SMC 23.44.050 lets certain stacked-dwelling-unit lots reach a 2.0 floor area ratio by meeting a Green Factor score of 0.6, among other options, showing the score set here has real zoning consequences beyond the landscaping plan itself.