Harlow Carr in Yorkshire
The gardens, which stand on what was once part of the Forest of Knaresborough, an ancient royal hunting ground, were started in 1950 by the Northern Horticultural Society (NHS) as a trial ground for growing plants in a northern climate. The RHS acquired the gardens in 2001 in a merger with the NHS. The gardens are known now for spectacular displays of color at every turn in the garden paths. Favorites include colorful candelabra primulas along a stream, blue poppies in the Meconopsis trial graden, and many different geranium species. Be sure to include the Alpine House on your must-see list.