The property is nationally significant as one of the most fully developed and authentic examples of the Country Place Era. Blithewold's owners Augustus and Bessie Van Wickle planted species from Europe and the Far East as well as North America. Nursery lists from 1908-1911 include hundreds of woody plants representing scores of species. Today there are about 500 species in a collection of approximately 2000 trees and shrubs. Metal plant labels identify many of the plants. Blithewold now boasts a variety of flowering trees and shrubs, weeping forms of deciduous and evergreen trees and venerable specimens of native trees.

Blithewold's trees have attracted attention throughout its history. The collection had its first recognition as an arboretum in 1926 when Ernest Henry Wilson and Alfred Rehder from Harvard’s Arnold Arboretum visited Blithewold to see the Chinese toon tree (Toona sinensis) in bloom for what was believed to be the first time in this country. Today the maturity of the collection as a whole is one of the character-defining features of the property, and it continues to draw visitors including botanists, garden groups and home gardeners looking for ideas and inspiration. The collection also is the home of nine Rhode Island state champion trees.