The Royal Horticultural Society of Ireland - Member-led society dedicated to promoting the knowledge, skill, and practice of horticulture, arboriculture and floral art. Founded in 1816 - http://www.rhsi.ie
The Royal Horticultural Society - Britain's Gardening Charity, founded in 1804 to encourage the science, art, and practice of horticulture in all its branches. - http://www.rhs.org.uk/