How Seasonwise works

Seasonwise (formerly GrowGuide) turns a US ZIP code into frost dates and planting windows. Everything runs in your browser from published government data; only the optional "Ask" helper contacts a server.

Frost dates

From the NOAA NCEI U.S. Climate Normals, 1991–2020 (annual/seasonal product). For more than 7,000 stations NOAA publishes the dates by which the last spring and first fall 32°F and 28°F freezes occur with 10%, 50% and 90% probability, and the frost-free season length exceeded in half of years. Stations where freezes are too rare to compute are treated as frost-free.

Matching your ZIP

Each ZIP Code Tabulation Area's internal point from the US Census Bureau 2023 Gazetteer is matched to the nearest station with freeze data (straight-line distance, up to 150 km). Distance and the station name are shown with every result. Elevation and terrain differences between you and the station are not corrected for.

Hardiness zones

From the 2023 USDA Plant Hardiness Zone Map ZIP code table, produced by the USDA Agricultural Research Service and Oregon State University's PRISM Climate Group.

Planting windows

Each crop has a window in weeks relative to the average last spring frost (for indoor starts, transplants and spring sowing) or the average first fall frost (for fall crops), based on common guidance from university extension vegetable planting guides. Soil temperatures and days-to-harvest ranges are typical values; your seed packet is the final word for a particular variety.

Risk curves

The frost-odds sliders fit a normal distribution to each station's 10%, 50% and 90% freeze dates. It is a smooth approximation between NOAA's published points, not a separate forecast.

The Ask helper

Questions typed into "Ask about your garden" are sent, with your ZIP's frost summary, to an AI language model through Vercel AI Gateway. Answers can be wrong; treat them like advice from a well-read neighbor.