University of Wisconsin Extension
1 Fen Oak Ct. #138
Madison, WI 53718
608-224-3700
http://hort.uwex.edu

American Horticultural Society
http://www.ahs.org/

Invasive Species
http://www.invasiveplants.net/
http://www.ipaw.org/

Wisconsin Master Gardeners Program
Department of Horticulture
1575 Linden Drive
University of Wisconsin – Madison
Madison, WI 53706
608-265-4504
http://wimastergardener.org

Plant Disease Diagnostics Clinic
Dept. of Plant Pathology
1630 Linden Dr.
Madison, WI 53706
http://www.plantpath.wisc.edu/index.php

Garden Catalogs (an extensive list with links)
http://www.gardenlist.com/
http://www.mailordergardening.com/

Madison Area Master Gardeners (MAMGA)
http://mamgawi.org/