State guide
Planting zones in New Hampshire
New Hampshire spans USDA zones 4a to 6b across its 246 ZIP codes, so there is no single zone for the state and anyone who gives you one is rounding. 41% of its ZIP codes are zone 6a; the rest are not.
Your ZIP code
Get the exact answer for your address
Everything above describes New Hampshire as a whole. Hardiness zones and freeze dates are published per ZIP code, so yours is exact — enter it and this page will tell you your zone, which NOAA station it comes from and how far away that station is.
Which zone you are in depends where you are
New Hampshire covers 6 hardiness zones. A guide that gives the state one zone has picked whichever is largest and rounded everyone else into it — which is fine for the 41% in zone 6a and wrong for the other 59%. Here is the actual split, by ZIP code.
| Zone | ZIP codes | Share | |
|---|---|---|---|
| 6a | 102 | 41% | |
| 5b | 74 | 30% | |
| 5a | 55 | 22% | |
| 4b | 9 | 4% | |
| 4a | 4 | 2% | |
| 6b | 2 | 1% |
Zones are published per ZIP code, so yours is exact even though the state's is not. The hardiness tool will tell you which one you are in.
Your freeze dates
Those are the earliest and latest medians among the 54 stations in New Hampshire with an ordinary freeze window — not an average, and not one station standing in for the rest. Half of years freeze later than a station's own median.
Your growing season
NOAA publishes a growing-season length for each station, and across the 54 stations in New Hampshire it runs 112–180 days . That figure is published, not computed from the two freeze dates — subtracting one from the other gives the wrong answer wherever a season crosses New Year. Mean summer high (June–August) runs 73–82 °F , below the 90 °F point where cool-season crops reliably bolt.
The ends of each range, named
A range with no station behind it cannot be checked, and New Hampshire has too many stations to table them all. So every figure above is reported here with the station standing at each end of it, by name and NOAA ID. No station on this page represents New Hampshire — these are its edges, which is a different claim.
| Measure | Earliest / lowest | Station | Latest / highest | Station |
|---|---|---|---|---|
| Last spring freeze | April 21 | Manchester AP, NH USW00014710 | May 31 | Colebrook 3Sw, NH USC00271647 |
| First fall freeze | September 18 | Bethlehem 2, NH USC00270706 | October 19 | Manchester AP, NH USW00014710 |
| Growing season | 112 days | Colebrook 3Sw, NH USC00271647 | 180 days | Manchester AP, NH USW00014710 |
| Mean summer high | 73 °F | First Connecticut Lake, NH USC00272999 | 82 °F | Nashua Cwsu, NH USC00275703 |
These are medians, not averages — NOAA publishes freeze dates as a probability distribution, and half of years freeze later than the date shown.
When to start seeds in New Hampshire
Every spring job for 63 crop dates, counted from this state's own last spring freeze. Each is a range across all 54 stations — the earliest and latest that job falls anywhere in New Hampshire — because no one station speaks for a whole state. The ranges are wide on purpose: that width is the state.
| Crop | Job | When | Offset |
|---|---|---|---|
| Green Onions | Start indoors | February 24 – April 5 | 8 weeks before |
| Peppers | Start indoors | February 24 – April 5 | 8 weeks before |
| Broccoli | Start indoors | March 10 – April 19 | 6 weeks before |
| Cabbage | Start indoors | March 10 – April 19 | 6 weeks before |
| Collards | Start indoors | March 10 – April 19 | 6 weeks before |
| Kale | Start indoors | March 10 – April 19 | 6 weeks before |
| Leaf Lettuce | Start indoors | March 10 – April 19 | 6 weeks before |
| Peas | Direct sow | March 10 – April 19 | 6 weeks before |
| Spinach | Direct sow | March 10 – April 19 | 6 weeks before |
| Sweet Potato | Start indoors | March 10 – April 19 | 6 weeks before |
| Tomatoes | Start indoors | March 10 – April 19 | 6 weeks before |
| Bok Choy | Start indoors | March 17 – April 26 | 5 weeks before |
| Kohlrabi | Start indoors | March 17 – April 26 | 5 weeks before |
| Swiss Chard | Start indoors | March 17 – April 26 | 5 weeks before |
| Arugula | Direct sow | March 24 – May 3 | 4 weeks before |
| Baby Salad Greens | Direct sow | March 24 – May 3 | 4 weeks before |
| Beets | Direct sow | March 24 – May 3 | 4 weeks before |
| Green Onions | Direct sow | March 24 – May 3 | 4 weeks before |
| Mustard Greens | Direct sow | March 24 – May 3 | 4 weeks before |
| Okra | Start indoors | March 24 – May 3 | 4 weeks before |
| Radishes | Direct sow | March 24 – May 3 | 4 weeks before |
| Turnips | Direct sow | March 24 – May 3 | 4 weeks before |
| Cabbage | Set out | March 31 – May 10 | 3 weeks before |
| Carrots | Direct sow | March 31 – May 10 | 3 weeks before |
| Collards | Direct sow | March 31 – May 10 | 3 weeks before |
| Collards | Set out | March 31 – May 10 | 3 weeks before |
| Cucumbers | Start indoors | March 31 – May 10 | 3 weeks before |
| Green Onions | Set out | March 31 – May 10 | 3 weeks before |
| Kale | Direct sow | March 31 – May 10 | 3 weeks before |
| Kale | Set out | March 31 – May 10 | 3 weeks before |
| Kohlrabi | Direct sow | March 31 – May 10 | 3 weeks before |
| Kohlrabi | Set out | March 31 – May 10 | 3 weeks before |
| Leaf Lettuce | Direct sow | March 31 – May 10 | 3 weeks before |
| Pumpkins | Start indoors | March 31 – May 10 | 3 weeks before |
| Summer Squash | Start indoors | March 31 – May 10 | 3 weeks before |
| Winter Squash | Start indoors | March 31 – May 10 | 3 weeks before |
| Zucchini | Start indoors | March 31 – May 10 | 3 weeks before |
| Bok Choy | Direct sow | April 7 – May 17 | 2 weeks before |
| Bok Choy | Set out | April 7 – May 17 | 2 weeks before |
| Broccoli | Set out | April 7 – May 17 | 2 weeks before |
| Cilantro | Direct sow | April 7 – May 17 | 2 weeks before |
| Leaf Lettuce | Set out | April 7 – May 17 | 2 weeks before |
| Swiss Chard | Direct sow | April 7 – May 17 | 2 weeks before |
| Swiss Chard | Set out | April 7 – May 17 | 2 weeks before |
| Dill | Direct sow | April 14 – May 24 | 1 week before |
| Bush Beans | Direct sow | April 28 – June 7 | 1 week after |
| Cucumbers | Set out | April 28 – June 7 | 1 week after |
| Pumpkins | Direct sow | April 28 – June 7 | 1 week after |
| Pumpkins | Set out | April 28 – June 7 | 1 week after |
| Summer Squash | Direct sow | April 28 – June 7 | 1 week after |
| Summer Squash | Set out | April 28 – June 7 | 1 week after |
| Sweet Corn | Direct sow | April 28 – June 7 | 1 week after |
| Tomatoes | Set out | April 28 – June 7 | 1 week after |
| Winter Squash | Direct sow | April 28 – June 7 | 1 week after |
| Winter Squash | Set out | April 28 – June 7 | 1 week after |
| Zucchini | Direct sow | April 28 – June 7 | 1 week after |
| Zucchini | Set out | April 28 – June 7 | 1 week after |
| Cucumbers | Direct sow | May 5 – June 14 | 2 weeks after |
| Okra | Direct sow | May 5 – June 14 | 2 weeks after |
| Okra | Set out | May 5 – June 14 | 2 weeks after |
| Peppers | Set out | May 5 – June 14 | 2 weeks after |
| Southern Peas | Direct sow | May 5 – June 14 | 2 weeks after |
| Sweet Potato | Set out | May 5 – June 14 | 2 weeks after |
The week offsets are conventional extension guidance and vary by variety; the freeze dates they are counted from are measured. For a single date rather than a range, run when do I start my seeds? with your own ZIP code.
What survives the winter changes across New Hampshire
Of 74 perennial fruits, nuts, berries, vegetables and herbs, 51 come through the winter in zone 6a and only 34 in zone 4a. Winter hardiness runs on the zone alone, so each row below is exact for the ZIP codes in it.
| Zone | ZIPs | Survive | Fail for being too warm |
|---|---|---|---|
| 4a | 4 | 34 of 74 | 0 |
| 4b | 9 | 34 of 74 | 0 |
| 5a | 55 | 48 of 74 | 0 |
| 5b | 74 | 48 of 74 | 0 |
| 6a | 102 | 51 of 74 | 0 |
| 6b | 2 | 51 of 74 | 0 |
The best zone in New Hampshire is 6a, which is not its mildest — 6b is. The count peaks in the middle and falls both ways, because the warm end loses plants to insufficient winter chill and summer heat rather than to cold. Most temperate fruit needs a documented number of hours below about 45 °F to break dormancy and set a crop, so an apple fails in a winter that is too warm; currants and rhubarb cook in the heat that comes with it. See the full list with reasons.
Your own ZIP
Work out your own dates
Each of these takes a ZIP code and answers for that ZIP alone, citing the station it used and how far away it is. There is a ZIP box in the header of every page.
- What survives my winter?
Runs on the hardiness zone, so it answers exactly for your ZIP code rather than for New Hampshire as a whole — 74 perennial fruits, berries, vegetables and herbs.
- When do I start my seeds?
Dates every spring job from your own last freeze — sow indoors, set out, direct sow.
- When do I sow the next round?
How often each crop is worth re-sowing, and when the next sowing is due.
- What can I still plant?
Counts the growing days left before your first fall freeze, crop by crop.
Metro areas in New Hampshire
2 metro areas here have its own page, with the freeze dates from every station serving it, a spring calendar built from those stations, and every ZIP code in it listed with that ZIP code's exact zone and nearest station.
- Boston-Cambridge-Newton, MA-NH Zones 5b–7a
- Manchester-Nashua, NH Zones 5b–6a
Counties in New Hampshire
7 countys here have its own page, listing every ZIP code in it with that ZIP code's exact zone and nearest station. These are the smaller places outside the metro areas above — where most of New Hampshire's ZIP codes actually are.
- Grafton County, NH Zones 4b–5b
- Carroll County, NH Zones 5a–5b
- Merrimack County, NH Zones 5a–6a
- Cheshire County, NH Zones 5b–6a
- Sullivan County, NH Zones 5a–6a
- Coos County, NH Zones 4a–5a
- Belknap County, NH Zone 5b
Other states to compare
Gear
If you want to act on this
Each link opens an Amazon search rather than a product we picked. We have not tested these and do not rank them — the search is the honest version, and you choose.
- Trunk wrapZone 4a is cold enough that winter sun on a young trunk does more damage than the cold does.
- Row cover and frost clothThe season here closes at the first fall freeze dated above — a cover buys back some of those days at the end.
- MulchFor the perennials nearest their cold limit in zone 4a, where an insulated crown is what decides whether they come back.
As an Amazon Associate we earn from qualifying purchases. That costs you nothing extra, and it buys no influence over anything on this site: the dates come from NOAA normals and the zones from the USDA, and no product affects either.
Sources
Where these numbers come from
The hardiness zone is the USDA 2023 Plant Hardiness Zone Map, published per ZIP code by PRISM at Oregon State. The freeze dates, growing seasons and summer highs are NOAA's 1991–2020 Climate Normals, read from every station in New Hampshire. Which ZIP codes are in New Hampshire comes from the Census ZIP-to-county relation, since a county's federal code begins with its state's. Nothing here is estimated.
This page names no single station for New Hampshire on purpose. Picking one to represent a state sounds reasonable and is not — the same reason the metro pages refuse it, only more so at this size. Instead every range names the station at each end, so you can check both without either one being made to speak for the state.