Issaquah, WA Invasive Plant Rules: Prohibited Species (2026)

The prohibition sits in Issaquah Land Use Code § 18.606.040(E)(4), part of the plant selection standards for landscape areas. After requiring plants that fit their space and minimize persistent pruning, it states that any class of noxious weeds, including nonregulated weeds and weeds of concern, per the King County Noxious Weed Control Board pursuant to the State Weed Control Law, Chapter 17.10 RCW, is not allowed. The paragraph does not print a City species roster: the King County list controls which plants fall under the ban.

Two definitions in Chapter 18.102 explain the terms. Section 18.102.130 defines "invasive tree" or "invasive plant" as a tree or plant listed as a weed of concern in Chapter 16-750 WAC, Chapter 17.10 RCW, or by King County in its noxious weed list. Section 18.102.180 defines "noxious weed" as having the same meaning as in RCW 17.10.010(8).

Trees face a second filter. Paragraph (E)(6) requires tree species to be selected from the City preferred and prohibited tree list, and § 18.606.040(H)(7) refers street trees to the same list. Under § 18.606.170(B), the City keeps a preferred tree list from which developers select, any tree chosen for public property that is not on the list requires City approval, and the list is subject to periodic updating and available at the permit center. Section 18.606.170(F) separately requires City permission before any plant is planted or removed on City property or public right-of-way.

Scope follows Chapter 18.606. Section 18.606.020 reaches new development, subdivision of property, development or redevelopment in, adjacent to, or affecting critical areas, and redevelopment that increases impervious surface area by 20 percent or more. Section 18.606.030 exempts single-family use lots with a detached single-family home, middle housing developments, accessory dwelling units, and projects with five or fewer new trees or 1,000 square feet of landscaping from the chapter's permitting and bonding requirements. The deviation list in § 18.606.190 names only irrigation water budgeting.