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| American Horticultural Society | Home page of this national association includes heat zone map, Master Gardener program information, youth gardening program materials and more. |
| Bowman's Hill Wildflower Preserve | Bucks County resource emphasizing native plants. |
| Bulb.com | Excellent overview of the bulb industry, including history. |
| Citation Styles-Online! A Reference Guide to Using Internet Sources | Examples of how to cite from APA, MLA, CSE and Chicago style manuals. |
| Gardenscape | Information resource for home gardeners and professionals in gardening, landscape, and nursery industries. |
| I Love Gardens.com | Nation-wide list of public and private gardens and arboreta, searchable by state. |
| International Herb Association | Professional trade association. Good list of links. |
| Invasive Species.gov | National Agricultural Library's resource rich site, focusing on plant and animal alien species that threaten native plants and animals. |
| Jobs in Horticulture | Current list of OH job opportunities |
| Pennsylvania Horticultural Society | Founded in 1827, PHS sponsors Philadelphia Flower Show, Green Scene Magazine and Gold Medal list of Plants for Delaware Valley region. |