Garden Societies by Plant Type
this list of sites compiled by the American Horticultural Society

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ahsgardening.org/gardening-resources/societies-clubs-organizations/societies-by-plant-type/
This list should help you find national companion plant societies to complement your hosta gardens.

If you haven't got a chance to familiarize yourself with this organization, please check them out too. 
The American Horticultural Society educates Americans about and advocates Earth-friendly and sustainable gardening practices, as well as models them at our River Farm headquarters in Alexandria, Virginia. 

www.https://ahsgardening.org