21ST ANNUAL PLANT SALE. Trees, shrubs, annuals, perennials, vines, herbs, heirloom tomatoes…no matter your passion, the plant sale has something for you! Purchase the best plants and have all your gardening questions answered by on-site experts. With over 20 years of experience, this is one sale you will not want to miss. The theme of this year’s highly anticipated sale, sponsored by the Friends of The Frelinghuysen Arboretum, is ‘The Collector’s Garden.’