Free tool
What growing zone am I in?
Type your town below and you’ll get your plant hardiness zone right away. Growmanac reads about a decade of daily low temperatures for your location, takes each year’s coldest day and averages them — that average is what the zone measures. It works anywhere on Earth, not just the US, and it’s free with no signup.
How we work it out
A hardiness zone is a label for one number: the average annual extreme minimum — how cold your coldest night usually gets. The scale runs from 1a (brutal) to 13b (no real winter), and each zone spans 10 °F, split into a colder a half and a milder b half.
So we fetch roughly ten years of daily minimum temperatures for your coordinates, pick out each year’s single coldest day, and average those. That average lands in one zone band, and that is your zone. Nothing is stored — the lookup happens in your browser and the answer is gone when you close the tab.
Reading your zone label
A zone is written as a number plus a letter — 7a, 9b, 11a. The number is the 10 °F (about 5.5 °C) band your average coldest night falls in; the letter splits that band in half, a being the colder 5 °F and b the milder one. So 7b is one step warmer than 7a, and 8a is one step warmer again.
Higher means milder. Nothing about the label describes heat, rain or how long your summer is — it is one number about winter, which is why two places with the same zone can garden quite differently.
What the number is good for — and what it isn’t
Your zone tells you what can survive your winter outdoors. That makes it the right question for perennials, shrubs and trees, and for deciding whether a tender plant needs to come in.
It tells you much less about timing. Two places can share a zone and still have very different springs, summer heat, and day length — so the zone alone won’t tell you when to sow, or whether your tomatoes will ripen. That’s a different question, and it’s the one the planner answers.
Your garden is not the regional average
The figure above describes your area. Your actual plot can sit half a zone either side of it, and the differences are big enough to matter:
- A south-facing wall (north-facing in the Southern hemisphere) soaks up sun all day and gives it back at night — the warmest spot you own.
- A city runs milder than the countryside around it; brick, tarmac and buildings hold heat.
- A frost pocket — the bottom of a slope, or a dip with a wall across it — collects cold air as it sinks and can be several degrees colder than ground twenty metres uphill.
- A container is the harshest of all. Soil in a bed loses heat only from the top; a pot loses it from every side, so the rootball can freeze while the same plant in the ground shrugs it off.
So treat the number as your starting point and let your own plot correct it. If a plant that "should" survive keeps dying in one spot, the spot is telling you something the map can't.
Zones get redrawn — and ours won’t always match the USDA’s
Zone maps are recalculated as new temperature records accumulate. When the USDA published its 2023 map, about half of the United States moved to the next warmer half zone and the other half stayed put. Worth reading carefully, though: the USDA attributes most of that shift to using a more recent period (1991–2020) and far more weather stations — 13,412 against 7,983 — rather than presenting it as a measure of climate change.
That is also why our answer can differ from the USDA’s for a US address: different records, different periods. Near a boundary the two are usually one half-zone apart. If they disagree, plan for the colder of the two — the cost of being wrong that way is a plant that does better than expected.
What to do with it today
Take your number to the next plant label or seed packet you pick up and compare. If the label’s zone is equal to or lower than yours, that plant can overwinter outside where you are. If it’s higher, you now know to grow it in something you can move. That one check is most of what the zone is for — and the planner turns it into a dated plan for this month.
Guidance, not a guarantee — your microclimate, soil and light have the final say. Climate data via Open-Meteo (ERA5 reanalysis).
Common questions
What growing zone am I in?
Enter your town above. Growmanac looks up about a decade of daily low temperatures for that spot, takes each year’s coldest day and averages them, then reads off the matching hardiness zone (1a to 13b) and the temperature band that zone stands for. It works anywhere on Earth.
Does this work outside the United States?
Yes. Hardiness zones started as a USDA system for the US, but the zone is just a label for your average coldest day — so it can be worked out for any location. Growmanac uses global climate data, which is why it answers for towns the USDA map has never covered.
Can my zone change, or be wrong for my garden?
Both. The maps get redrawn as newer temperature records come in, and your own plot can sit half a zone either side of the regional figure — a sheltered courtyard or a warm city runs milder, an exposed balcony or a valley floor runs colder. Treat the zone as a starting point, not a verdict.
Why is this different from the USDA zone for my address?
Because they are built from different records. The USDA’s 2023 map uses weather-station data from 1991 to 2020; Growmanac uses a global gridded climate dataset and roughly the last decade, so a location near a zone boundary can land on either side. If you are in the US and the two disagree, they are usually one half-zone apart — take the colder of the two and you will not be caught out.
Do plants in pots survive the same zone as plants in the ground?
No — assume a pot is harsher. Soil in the ground holds warmth and only loses it from the top, while a container is exposed on every side, so its rootball can freeze when the same plant in a bed would be fine. Gardeners commonly plan a zone or two hardier for anything meant to overwinter in a pot, or move the pot against a wall or indoors.
A plant label says “hardy to zone 6” — what does that mean for me?
It means the plant is expected to survive winter outdoors in zone 6 and anywhere milder, so read it as “zone 6 or higher”. If your zone number is equal to or higher than the label, it should come through winter where you are; if yours is lower, it will need protection, a container you can move, or treating as an annual.