Free Growli tool
ZIP code to USDA zone
— frost dates and what to plant.
Type a 5-digit US ZIP — we'll return your USDA hardiness zone, average first and last frost dates, growing-season length, and the crops that match this week of the year. UK postcodes route through to the RHS hardiness guide.
MVP coverage: ~250 of the largest US metros, plus all 50 state capitals. Full 42,000-ZIP coverage is rolling out — accuracy first.
We cover the top ~250 US metros today — full ZIP coverage is coming soon.
Type a 5-digit US ZIP code (e.g. ) or a UK postcode (e.g. SW1A 1AA) to get your USDA hardiness zone, frost dates, and a what-to-plant-now recommendation calibrated to your local growing season.
Try a sample ZIP
Each of these dedicated growing pages has zone, frost dates, planting calendar, and a crop-by-crop sowing timeline for that specific city:
How this works
Each US ZIP is mapped to one of the 13 USDA hardiness zones (1a-13b) using the 2023 USDA Plant Hardiness Zone Map. Zones are based on the average annual minimum winter temperature — Zone 1 is the coldest (-60 to -50 °F), Zone 13 the hottest tropical band (60 to 70 °F).
Frost-date averages are pulled from the NOAA 1991-2020 climate normals. These are 50% probability dates — the date by which last frost has occurred in half of recent years. Local elevation, urban heat islands, lakes, and slopes can shift them by ±10 days.
What this tool does notcapture: medical or food-safety advice, current weather (cold snaps, heatwaves), your specific microclimate, or your soil's actual readiness. Always check soil temperature before planting tender crops — the Growli app does this continuously based on your specific garden.
Frequently asked questions
How accurate are the frost dates?
They're 50% probability averages drawn from the NOAA 1991-2020 climate normals — i.e. the date you'd expect the last spring frost in a typical year. Real local variability is roughly ±10 days, and microclimates (urban heat, south-facing slopes, lakeside warmth) shift dates further. Treat them as a planning baseline, not a guarantee.
Why is my ZIP not in the lookup?
For v1 we curated the top ~250 US metros where accuracy matters most. Full US ZIP coverage (≈42,000 codes) is rolling out — until then, the official USDA Plant Hardiness Zone map at planthardiness.ars.usda.gov returns a zone for every US ZIP.
What about UK postcodes?
The USDA system is US-specific. In Britain we use the RHS hardiness rating scale (H1a to H7), which better reflects the UK's mild maritime winters and shorter growing seasons. Enter a UK postcode and we'll route you to our RHS rating guide where you can pick the band that fits your area.
What does USDA zone "7b" mean vs "Zone 7"?
The USDA splits each whole zone into a (colder half) and b (warmer half), each covering a 5 °F band. Zone 7a is -15 to -10 °F, Zone 7b is -10 to -5 °F. The half-band matters for borderline-hardy perennials (figs, camellias, some roses). For most annual vegetables the whole zone is enough.
How is this different from Growli's in-app planner?
This lookup is a one-shot answer for "what zone am I in and what should I plant this week?". The Growli app remembers your specific plants, adjusts for actual current weather (a heatwave or late cold snap), and lets you log when you actually planted — so future suggestions get smarter. The web tool gives you the snapshot; the app gives you the schedule.
Where does the "what to plant this week" recommendation come from?
We compare today's date to your ZIP's last and first frost dates. If you're within six weeks of either, we surface the seasonal window crops (tomatoes and peppers near last frost; garlic and brassicas near first frost). Outside those windows we suggest planning-and-prep work. Crop slugs link through to detailed sowing and harvest calendars for your specific zone.