Exploratorium: Science Of Gardening - Features articles and videos on several topics, including gardening with nature, carnivorous plants, soils, fruits, and vegetables, propagation, and plant reproduction.
Garden Ideas - Articles and advice on a variety of gardening topics.
Garden Terms - Gardening dictionary with brief definitions of a large number of terms, optionally arranged by category.
Gardening For Nutrition - Guidance for gardening and food intake with the purpose of maximizing nutrition.
Hort.net - Offers a collection of garden reference materials, including a plant gallery and profiles, archives of mailing lists, gardening news, and links.
Let's Go Gardening - General gardening site, with versions geared towards US and UK gardeners. Tips and articles, informational resources, links to events, societies, and public gardens, and a forum.
LoveToKnow Garden - Short informational articles on gardening topics, vegetables, and ornamental plants, contributed and edited by users.
MyGardenGuide - Offers plant database with photos and summary information, questions and answers on various garden topics, and a garden weblog.
Ohio State University PlantFacts - Collection of horticultural resources, including a search engine drawing from U.S. university factsheets, plant image database, how-to videos, illustrated FAQs, and glossary.
Yardener.com - Lawn and garden resources for homeowners whose garden is not their hobby. Includes information and care data for many plants, shrubs, and trees, and dealing with pests and problems.