Source Bibliography
The primary horticultural references cited across this site.
Every factual claim on this site cites a primary source. The complete list of references used across the site is below, grouped by publisher. Individual guides include inline citations to specific pages within these resources.
Federal references
- 2023 USDA Plant Hardiness Zone Map. The standard reference for cold hardiness in North American gardening. Updated November 2023 from the 2012 edition.
- NOAA National Centers for Environmental Information — Climate Normals. Average first and last frost dates, growing degree days, and other climate normals.
University Extension — Northeast and Mid-Atlantic
- Cornell Cooperative Extension. New York state Extension. Vegetable, fruit, and ornamental guidance.
- Penn State Extension. Particularly strong on woody ornamentals and pruning guidance.
- Rutgers New Jersey Agricultural Experiment Station. Includes the Landscape Plants Rated by Deer Resistance publication (E271).
- University of Maryland Extension Home & Garden Information Center. Mid-Atlantic ornamental and vegetable guidance.
- UMass Extension Center for Agriculture, Food, and the Environment. New England-region guidance.
University Extension — Southeast
- NC State Extension Plant Toolbox. Comprehensive species and cultivar database. The most-cited single source on this site.
- Clemson Cooperative Extension Home & Garden Information Center. South Carolina-based with broad Southeast applicability.
- University of Georgia Extension. Particularly for warm-zone vegetable and ornamental guidance.
- University of Florida IFAS Extension. Subtropical/tropical reference for zone 9+.
University Extension — Midwest
- University of Minnesota Extension. Strong on cold-climate woody plants and pruning.
- University of Illinois Extension. Broad horticultural reference.
- Iowa State University Extension and Outreach. Particularly for prairie and Midwest natives.
- Purdue University Extension.
University Extension — West
- Oregon State Extension Service. Pacific Northwest reference.
- UC Statewide Integrated Pest Management Program (UC IPM). The standard for pest and disease identification in North America.
- University of California Master Gardener Program.
- Washington State University Extension.
Botanical gardens
- Missouri Botanical Garden Plant Finder. The most-cited plant database in North American horticulture. Includes detailed culture, problem, and cultivar profiles.
- Royal Horticultural Society (RHS) Find a Plant. UK-based but globally relevant.
- Chicago Botanic Garden Plant Information Service.
- Brooklyn Botanic Garden.
Animal welfare
- ASPCA Animal Poison Control. Phone: (888) 426-4435. Cited for any plant-toxicity claim affecting cats or dogs.
- ASPCA Toxic and Non-Toxic Plants Database.
How citations work on this site
Inline citations appear in the body text in the form "Per [source], [claim]" with a link to the specific source page. Each guide ends with a numbered list of sources cited within that guide. This site does not use footnote-style references because they break the reading flow of long-form horticultural writing.
If you find a claim on this site without a citation, it is either (a) something I have observed firsthand in my own garden (clearly attributed to first-person experience), or (b) an error. If it's an error, email me — corrections are welcomed and applied promptly.