Sources and licenses
Every date and zone on this site is built from public records, and every planting time from published university guidance. This page lists each source, what we use it for and its license. Naming a source does not mean that agency or university endorses this site.
| Data | Source | Used for | License |
|---|---|---|---|
| Spring and fall freeze dates at 32 °F and 28 °F, with 10, 50 and 90% odds; growing season length | NOAA National Centers for Environmental Information, U.S. Climate Normals 1991-2020, annual and seasonal normals by station | Frost dates, all planting dates | U.S. federal data, public domain (17 U.S.C. 105) |
| Lowest temperature of each year, 1991-2020 | NOAA National Centers for Environmental Information, Global Summary of the Year (EMNT), by station | Growing zones (our own calculation) | U.S. federal data, public domain (17 U.S.C. 105) |
| Town and postal code (ZCTA) locations | U.S. Census Bureau, Gazetteer Files 2024; population estimates 2024 | Town and postal code search | U.S. federal data, public domain (17 U.S.C. 105) |
| Crop timing, spacing, depth, days to harvest, pruning windows | University cooperative extension publications (42 services, listed below and on each page) | When to plant, harvest and prune; companion planting | Facts only, rewritten in our words; each guide keeps its own copyright |
| Fonts | Young Serif, Work Sans and DM Mono, served from our own server | All pages | SIL Open Font License 1.1 |
| Site code | Astro (static site generator) | Building the pages | MIT |
What we do not use
- The official USDA Plant Hardiness Zone Map and its GIS files. Our zones apply the same definition to NOAA station records; they are not the official map.
- Almanacs, garden company charts and other sites' tables. Only public records and university publications.
- Agency or university logos, seals or insignia.
Extension services we cite
Clemson Cooperative Extension HGIC; Clemson Cooperative Extension, Home and Garden Information Center; Colorado State University Extension; Colorado State University Extension (PlantTalk); Cornell Cooperative Extension, Rockland County; Cornell Cooperative Extension, Warren County; Cornell University, Cornell Garden-Based Learning; Cornell University, Cornell Gardening Resources; Iowa State University Extension; Kansas State University Research and Extension; NC State Extension; NC State Extension Plant Toolbox; North Dakota State University Extension; Ohio State University Extension; Ohio State University Extension (Ohioline); Oregon State University Extension; Oregon State University Extension (PNW 400); Oregon State University Extension Service; Penn State Extension; Purdue Extension; South Dakota State University Extension; Texas A&M AgriLife Extension; Texas A&M AgriLife Extension, Travis County; Texas A&M AgriLife Today; UC Cooperative Extension, Placer and Nevada Counties; UF/IFAS Extension; UF/IFAS Gardening Solutions; UGA Extension; UGA Extension Fulton County; University of Arkansas Cooperative Extension; University of California Agriculture and Natural Resources, UC Master Gardener Program; University of Florida IFAS Gardening Solutions; University of Georgia Extension; University of Illinois Extension; University of Maine Cooperative Extension; University of Maryland Extension; University of Maryland Extension (Maryland Grows); University of New Hampshire Extension; University of Wisconsin-Madison Division of Extension; University of Wisconsin-Madison Extension; Utah State University Extension; Virginia Cooperative Extension (Virginia Tech).
Notes
- Works of the U.S. federal government are not protected by copyright (17 U.S.C. 105). Facts and figures are not protected by copyright either; the wording of the extension guides is, so we write our own.
- Frost dates are probabilities from past records, not forecasts. Your local extension office has the final word on timing for your area.