The Koko Crater Botanical Garden is a botanical garden located within the Koko Crater on the eastern end of Oahu, Hawaii. It was given the dual title of the Charles M. Wills Cactus Garden by the Honolulu Department of Parks and Recreation, in recognition of his contributions to the garden, in 1966.
The garden is part of the Honolulu Botanical Gardens, and first established in 1958. Its hot, dry climate is suitable for Plumeria and Bougainvillea cultivars in the outer crater, kiawe and koa haole trees, and four major collections organized by region. Other collections include adeniums, alluaudias, aloes, baobabs, cacti, euphorbias, palms, and sansevierias, as well as a native grove of wiliwili trees. A loop trail runs through the collections. They have about 500 trees and 200 species of trees.