The following are but some among the reference materials we utilize:

CONIFERS - THE ILLUSTRATED ENCYCLOPEDIA, D.M. van Gelderen and J.R.P. van Hoey Smith

DIRR'S HARDY TREES AND SHRUBS, Michael A. Dirr

THE EXPLORER'S GARDEN: SHRUBS and VINES From the Four Corners of the World, Daniel J. Hinkley

THE EXPLORER'S GARDEN: RARE and UNUSUAL PERENNIALS, Daniel J. Hinkley

LANDSCAPE PLANTS OF EASTERN NORTH AMERICA, Harrison L. Flint

MANUAL OF WOODY LANDSCAPE PLANTS, Michael A. Dirr

ORNAMENTAL CONIFERS, Julie Grace

PLANTS THAT MERIT ATTENTION: Volume I - TREES, Volume II - SHRUBS, Janet Meakin Poor and Nancy Peterson Brewster

THE REFERENCE MANUAL OF WOODY PLANT PROPAGATION: From Seed to Tissue Culture, Michael A. Dirr and Charles W. Heuser, Jr.

And we refer to the following online source with regularity: UCONN PLANT DATABASE OF TREES, SHRUBS AND VINES by Mark H. Brand