American Bamboo Society: Provides a source of information on the identification, propagation, utilization, and culture of bamboos.
American Bamboo Society – Pacific Northwest Chapter: The Chapter has year-round activities and meetings, generally held in Seattle, Tacoma, Federal Way, Portland and Vancouver.
American Fern Society: Established in 1893 with the objective of fostering interest in ferns and fern allies.
American Orchid Society: The American Orchid Society is established for scientific and/or educational purposes related to the study of orchids, their propagation, preservation and perpetuation, culture, care and development.
Bromeliad Society International: The purposes of this society are to promote and maintain public and scientific interest in the research, development, preservation, and distribution of bromeliads, both natural and hybrid. The site has a list of frequently asked questions and good information about the plants.
Bromeliad Society of San Francisco: They are dedicated to the growth and spread of horticultural and scientific knowledge of the Bromeliad Family (Bromeliaceae) and the preservation of its species and habitats.
Cascade Cactus & Succulent Society of Washington: Meets University of Washington, Center for Urban Horticulture, Seattle WA, 2pm 3rd Sunday each month.
Cactus & Succulent Society of America: Has a worldwide membership and publishes a journal with information on cacti and succulent plants.
Elizabeth C. Miller Library: The Miller Library at the University of Washington Center for Urban Horticulture is a good resource for gardening and plant related questions.
The Garden Web: The largest gardening site on the Web, with garden forums, articles on gardening, directories of nurseries, gardens and gardening organizations.
Gardening with Ciscoe: Local information about gardening and plant events and an extensive list of useful links.
International Palm Society: Members worldwide growing palm trees of all varieties in a wide range of climates.
Kruckeberg Botanic Garden Foundation: The Kruckeberg Botanic Garden at Richmond Beach, in Shoreline, Washington, is dedicated to the educational, cultural and aesthetic enrichment of the community and all who visit. Mareen and Arthur Kruckeberg assembled the Garden’s four-acre plant collection over many years. It is rich in native plants of the Pacific Northwest, and unusual species from other lands, set in a wooded, park-like atmosphere.
Northwest Orchid Society: Meets the 2nd Monday, monthly, except August, 7:00 p.m. at the Center for Urban Horticulture
Northwest Perennial Alliance: The Northwest Perennial Alliance is a group of Seattle gardeners passionate about perennials and eager to share their knowledge with others formed the Northwest Perennial Alliance.
Today the NPA is one of the largest nonprofit gardening organizations in the Northwest, with more than 1,400 members from Snohomish to Olympia and beyond.
Seattle Youth Garden Works: Seattle Youth Garden Works empowers homeless and under-served youth through garden-based education and employment. The SYGW is a market gardening program for youth ages 14-22 in the University District and South Park neighborhoods. Project goals are to connect youth to housing, health care, education, jobs and community.