Methodology
How GrowZone turns a ZIP code into a planting calendar.
GrowZone maps supported ZIP codes to a representative frost station and USDA hardiness zone, then applies crop-specific timing rules. Reviewed by GrowZone Editorial.
Data stack
- NOAA/NWS climate normals for representative last-spring and first-fall frost timing at frost stations.
- USDA Plant Hardiness Zone data for the long-term winter cold band shown next to each calendar.
- ZIP → representative frost station mapping for supported ZIPs (planning signal, not a yard-level sensor).
- Crop timing rules for each of the 13 supported crops: start-indoors offset, transplant lag, direct-sow window, and days to harvest.
Worked example: ZIP 30301 tomatoes
- ZIP 30301 (Atlanta, GA) maps to frost station atlanta-hartsfield.
- That station carries last spring frost around Mar 29 and first fall frost around Nov 10 (~226 frost-free days), USDA zone 8a.
- Tomato rules start seeds indoors about six weeks before transplant, then transplant after the frost-risk window, which for this ZIP lands around Apr 5.
- The live answer page shows the bold date, the station + zone source line, FAQ schema, and a local-verification disclaimer.
Update cadence
USDA hardiness inputs refresh when USDA publishes a new map release (checked at least annually). NOAA/NWS climate-normal and representative frost-station inputs are recomputed before the February-May seed-starting peak and again before fall-planting content. Each generated page carries the current source/version date so stale data is visible instead of hidden.
Local verification
Gardeners should verify with local cooperative extension guidance, especially for unusual microclimates, high-value crops, or current-year weather anomalies. GrowZone is a planning signal, not a forecast.
Who reviews this
Named reviewer: GrowZone Editorial. Process: every answer page must show a computed date, station/zone source trail, FAQ schema when applicable, and the local-verification disclaimer before it ships. See also About GrowZone.
Measurement
GrowZone reports canonical metrics through /api/metrics and partner API hooks. The metric keys are sessions, pageviews, indexed_pages, email_signups, affiliate_clicks, affiliate_revenue, and ad_revenue. GA4 is optional and never replaces the canonical metrics contract.