Alien Invaders

In Washington state, Scotch broom (Cytisus scoparius) clearly belongs on the invasive-species list. I have seen it in its native Scotland, and it is beautiful with its butter-gold blossoms. However, in the mild, moist climate of western Washington, with no natural controls to hold it in check, it blankets the countryside. The official lists of noxious weeds also include butterfly bush (Buddleia davidii), which plant nurseries promote for butterfly gardens, and salt cedar (Tamarix ramosissima).

What can landscape architects and designers do? Gaining knowledge and understanding of the issue is a logical first step–to learn to identify the invasive plants of the region in which we practice. The lists provided for each state on the website noted above can help, as can a conversation with the local county-extension agent. You can find a list of the federal noxious weeds at

In our designs, we do not need to feel restricted to native or indigenous plants, but ethically we should only specify non-invasive plants. Furthermore, if a project property borders a natural area, strong consideration should be given towards using only native plants.

If the site already harbors invasive species, advise a client on the need to remove invasive plants or prevent their spread. The Center for Invasive Plant Management ( offers assistance in the ecologically sound management of invasive plants.

Plants naturally need to reproduce, and when those plants are alien invaders, the result has an undesirable ecological impact. Hopefully, landscape architects will employ best practices and be part of the solution and not the problem.

Don Brigham, Jr. is a landscape architect with over 29 years of experience designing spaces for the enjoyment of people. His firm is headquartered along the Washington-Idaho border from which he serves clients throughout the northwest. Since 1984, he has served as Adjunct Faculty in the Landscape Architecture Department at the University of Idaho.

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