Wash. Rev. Code § 47.40.030
Any person, firm, corporation, association, or organization owning lands abutting upon any state highway and desiring to plant, cultivate, and grow any hedge, shade trees, or ornamental trees or shrubs along the right-of-way thereof, or to clear and cultivate a portion of the state highway right-of-way for the purpose of growing crops and destroying noxious weeds, or any person, firm, corporation, association, or organization interested in public improvement and desiring to improve and beautify any state highway right-of-way or any portion thereof by planting, cultivating, or growing any hedge or shade or ornamental trees or cultivate along or upon the right-of-way thereof, may upon application to the department, be granted a permit therefor as provided by law.
RCW 47.40.030