New Hampshire
Planting zones in Merrimack County, New Hampshire
This county spans USDA zones 5a to 6a, so there is no single zone for Merrimack County and anyone who gives you one is rounding. 82% of its ZIP codes are zone 5b; the rest are not.
Your ZIP code
Get the exact answer for your address
Everything above describes Merrimack County, 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.
The growing season in Merrimack County is closing
Nothing in the 32-crop table still has time to mature here. The first fall freeze normally arrives September 26 – October 11 across the 9 NOAA stations serving this county .
Your next season already has a date
The first job of it is 🧅 Green Onions, start indoors, around March 5 – March 26 — counted back from a last spring freeze of April 30 – May 21 here.
These are ranges across the whole county. The ZIP lookup above gives the dates from your own nearest station instead.
All 9 stations agreeAt least one station
Every one of the 9 NOAA stations serving this county counts May 21 – September 26 as growing season (128 days). Widening to any single station gives April 30 – October 11 (164 days).
That is a 36-day difference inside one county — which is why this page gives ranges rather than a single planting date. The ZIP lookup above resolves it to one station.
Which zone you are in depends where you are
Merrimack County covers 3 hardiness zones. A guide that gives the county one zone has picked whichever is largest and rounded everyone else into it — fine for the 82% in zone 5b and wrong for the other 18%. Here is the actual split.
| Zone | ZIP codes | Share | |
|---|---|---|---|
| 5b | 23 | 82% | |
| 6a | 4 | 14% | |
| 5a | 1 | 4% |
Zones are published per ZIP code, so yours is exact even though the county's is not. The hardiness tool will tell you which one you are in.
Your freeze dates
Across the 9 NOAA stations serving this county. These are medians — half of years freeze later than the date shown — so treat the later end of each range as the cautious one.
The growing season runs 127–164 days depending which station you are nearest, as published by NOAA rather than computed from the dates above. Summer highs average 76.9–80.8 °F in June–August. Summer rain over the same months runs 11.0–13.0" across those 8 stations, against the rough inch a week — about 13 inches over the same 92 days — that a vegetable garden is usually reckoned to want. The middle station covers about 95% of it, so expect to make up the rest. The inches are NOAA's published normals; the inch a week is a rule of thumb, and it takes no account of a 78 °F summer afternoon drying the soil faster than a cool one.
Every ZIP code in Merrimack County
Zones are published per ZIP code, not per county, so this is the exact answer rather than the county's average. The station column is the nearest one to that ZIP code's centroid and how far away it is — the same figure the tools use, shown here so you can see which ZIP codes are well covered and which are reaching.
| ZIP code | USDA zone | Nearest NOAA station | Distance |
|---|---|---|---|
| 03046 | 6a | Weare, NH | 11.1 km |
| 03106 | 6a | Massabesic Lake, NH | 11.1 km |
| 03216 | 5b | Franklin Falls Dam, NH | 11.3 km |
| 03221 | 5b | Bradford 2, NH | 3.4 km |
| 03224 | 5b | Salisbury, NH | 15.3 km |
| 03229 | 5b | Hopkinton Lake, NH | 4.3 km |
| 03230 | 5a | Grafton, NH | 8.1 km |
| 03231 | 5b | Franklin Falls Dam, NH | 8.4 km |
| 03233 | 5b | Mt Sunapee, NH | 15.7 km |
| 03234 | 5b | Concord Muni AP, NH | 12.4 km |
| 03235 | 5b | Franklin Falls Dam, NH | 2.9 km |
| 03242 | 5b | Hopkinton Lake, NH | 7.2 km |
| 03243 | 5b | Franklin Falls Dam, NH | 11.3 km |
| 03255 | 5b | Mt Sunapee, NH | 4.9 km |
| 03257 | 5b | Mt Sunapee, NH | 11.9 km |
| 03258 | 5b | Concord Muni AP, NH | 10.8 km |
| 03260 | 5b | Mt Sunapee, NH | 13.6 km |
| 03263 | 5b | Concord Muni AP, NH | 18.7 km |
| 03268 | 5b | Salisbury, NH | 4.6 km |
| 03273 | 5b | Bradford 2, NH | 7.7 km |
| 03275 | 6a | Concord Muni AP, NH | 7.1 km |
| 03276 | 5b | Franklin Falls Dam, NH | 7.6 km |
| 03278 | 5b | Salisbury, NH | 9.5 km |
| 03287 | 5b | Grafton, NH | 13.9 km |
| 03301 | 5b | Concord Muni AP, NH | 6.6 km |
| 03303 | 5b | Salisbury, NH | 7.5 km |
| 03304 | 6a | Concord Muni AP, NH | 7.5 km |
| 03307 | 5b | Concord Muni AP, NH | 16.0 km |
ZIP-code positions are area centroids, so a large rural ZIP code's listed distance is measured from the middle of its area rather than from any particular address in it.
When to start seeds in Merrimack County
Every date below is anchored on the last spring freeze at each station and reported as a range across all 9 of them, because no one station speaks for the county.
| Crop | Job | When | Offset |
|---|---|---|---|
| 🧅 Green Onions | Start indoors | March 5 – March 26 | 8 wk before |
| 🌶️ Peppers | Start indoors | March 5 – March 26 | 8 wk before |
| 🥦 Broccoli | Start indoors | March 19 – April 9 | 6 wk before |
| 🥬 Cabbage | Start indoors | March 19 – April 9 | 6 wk before |
| 🥬 Collards | Start indoors | March 19 – April 9 | 6 wk before |
| 🥬 Kale | Start indoors | March 19 – April 9 | 6 wk before |
| 🥬 Leaf Lettuce | Start indoors | March 19 – April 9 | 6 wk before |
| 🫛 Peas | Direct sow | March 19 – April 9 | 6 wk before |
| 🥬 Spinach | Direct sow | March 19 – April 9 | 6 wk before |
| 🍠 Sweet Potato | Start indoors | March 19 – April 9 | 6 wk before |
| 🍅 Tomatoes | Start indoors | March 19 – April 9 | 6 wk before |
| 🥬 Bok Choy | Start indoors | March 26 – April 16 | 5 wk before |
| 🥬 Kohlrabi | Start indoors | March 26 – April 16 | 5 wk before |
| 🥬 Swiss Chard | Start indoors | March 26 – April 16 | 5 wk before |
| 🥬 Arugula | Direct sow | April 2 – April 23 | 4 wk before |
| 🥬 Baby Salad Greens | Direct sow | April 2 – April 23 | 4 wk before |
| 🥕 Beets | Direct sow | April 2 – April 23 | 4 wk before |
| 🧅 Green Onions | Direct sow | April 2 – April 23 | 4 wk before |
| 🥬 Mustard Greens | Direct sow | April 2 – April 23 | 4 wk before |
| 🌶️ Okra | Start indoors | April 2 – April 23 | 4 wk before |
| 🌱 Radishes | Direct sow | April 2 – April 23 | 4 wk before |
| 🥔 Turnips | Direct sow | April 2 – April 23 | 4 wk before |
| 🥬 Cabbage | Set out | April 9 – April 30 | 3 wk before |
| 🥕 Carrots | Direct sow | April 9 – April 30 | 3 wk before |
| 🥬 Collards | Direct sow | April 9 – April 30 | 3 wk before |
| 🥬 Collards | Set out | April 9 – April 30 | 3 wk before |
| 🥒 Cucumbers | Start indoors | April 9 – April 30 | 3 wk before |
| 🧅 Green Onions | Set out | April 9 – April 30 | 3 wk before |
| 🥬 Kale | Direct sow | April 9 – April 30 | 3 wk before |
| 🥬 Kale | Set out | April 9 – April 30 | 3 wk before |
| 🥬 Kohlrabi | Direct sow | April 9 – April 30 | 3 wk before |
| 🥬 Kohlrabi | Set out | April 9 – April 30 | 3 wk before |
| 🥬 Leaf Lettuce | Direct sow | April 9 – April 30 | 3 wk before |
| 🎃 Pumpkins | Start indoors | April 9 – April 30 | 3 wk before |
| 🎃 Summer Squash | Start indoors | April 9 – April 30 | 3 wk before |
| 🎃 Winter Squash | Start indoors | April 9 – April 30 | 3 wk before |
| 🥒 Zucchini | Start indoors | April 9 – April 30 | 3 wk before |
| 🥬 Bok Choy | Direct sow | April 16 – May 7 | 2 wk before |
| 🥬 Bok Choy | Set out | April 16 – May 7 | 2 wk before |
| 🥦 Broccoli | Set out | April 16 – May 7 | 2 wk before |
| 🌿 Cilantro | Direct sow | April 16 – May 7 | 2 wk before |
| 🥬 Leaf Lettuce | Set out | April 16 – May 7 | 2 wk before |
| 🥬 Swiss Chard | Direct sow | April 16 – May 7 | 2 wk before |
| 🥬 Swiss Chard | Set out | April 16 – May 7 | 2 wk before |
| 🌿 Dill | Direct sow | April 23 – May 14 | 1 wk before |
| 🫘 Bush Beans | Direct sow | May 7 – May 28 | 1 wk after |
| 🥒 Cucumbers | Set out | May 7 – May 28 | 1 wk after |
| 🎃 Pumpkins | Direct sow | May 7 – May 28 | 1 wk after |
| 🎃 Pumpkins | Set out | May 7 – May 28 | 1 wk after |
| 🎃 Summer Squash | Direct sow | May 7 – May 28 | 1 wk after |
| 🎃 Summer Squash | Set out | May 7 – May 28 | 1 wk after |
| 🌽 Sweet Corn | Direct sow | May 7 – May 28 | 1 wk after |
| 🍅 Tomatoes | Set out | May 7 – May 28 | 1 wk after |
| 🎃 Winter Squash | Direct sow | May 7 – May 28 | 1 wk after |
| 🎃 Winter Squash | Set out | May 7 – May 28 | 1 wk after |
| 🥒 Zucchini | Direct sow | May 7 – May 28 | 1 wk after |
| 🥒 Zucchini | Set out | May 7 – May 28 | 1 wk after |
| 🥒 Cucumbers | Direct sow | May 14 – June 4 | 2 wk after |
| 🌶️ Okra | Direct sow | May 14 – June 4 | 2 wk after |
| 🌶️ Okra | Set out | May 14 – June 4 | 2 wk after |
| 🌶️ Peppers | Set out | May 14 – June 4 | 2 wk after |
| 🫘 Southern Peas | Direct sow | May 14 – June 4 | 2 wk after |
| 🍠 Sweet Potato | Set out | May 14 – June 4 | 2 wk after |
Offsets are published guidance; the dates they land on are computed from measured NOAA normals. The seed-starting tool does this for your own ZIP code and counts the days.
What survives the winter changes across Merrimack County
Zone 6a carries 51 of 74 perennial edibles; zone 5a carries 48. The best number is not always the warmest zone — the count peaks in the middle and falls both ways, because the warm end loses plants to insufficient winter chill and summer heat, not to cold.
Hardiness ranges are a judgement, published by growers rather than measured; the zone they are compared against is measured. On a warm-end verdict, check with your local extension service — a coastal zone 8 and an inland zone 8 are not the same summer.
Cautious — shortens the seasonMedian across stationsOptimistic
- Last spring freeze
- Plan to June 5 to be careful. Median April 30 – May 21 across 9 stations; April 19 is the optimistic end.
- First fall freeze
- Plan to September 12 to be careful. Median September 26 – October 11 across 9 stations; October 27 is the optimistic end.
NOAA publishes these as probabilities, not averages — the middle figure is a median, so half of years fall either side of it. The cautious end is the 10% tail: in roughly nine years in ten the freeze falls on the safe side of it.
The 9 stations behind these numbers
All 9 NOAA stations whose normals this page quotes, spanning about 64 km north to south. Every one is named with its identifier in the station list below — this page does not single one out, because no one station speaks for a whole county.
A relative sketch, not a map with a projection: longitude is adjusted for latitude so the shape is not stretched, and there is no basemap. For the one station nearest a specific address, with its real distance, use the ZIP lookup above.
These are the stations this county's ZIP codes actually cite as nearest — not a claim that each one sits inside its boundary, since a rural ZIP legitimately reaches over it. Every figure above comes from them, and each is named so you can check it.
| Station | NOAA ID | Last spring freeze | First fall freeze | Season |
|---|---|---|---|---|
| Bradford 2, NH | USC00270913 | May 15 | September 27 | 135 days |
| Concord Muni AP, NH | USW00014745 | May 8 | October 3 | 146 days |
| Franklin Falls Dam, NH | USC00273182 | May 7 | October 3 | 148 days |
| Grafton, NH | USC00273530 | May 21 | September 26 | 127 days |
| Hopkinton Lake, NH | USC00274218 | May 6 | October 1 | 146 days |
| Massabesic Lake, NH | USC00275211 | April 30 | October 11 | 164 days |
| Mt Sunapee, NH | USC00275629 | May 2 | October 9 | 158 days |
| Salisbury, NH | USC00277833 | May 14 | September 29 | 138 days |
| Weare, NH | USC00278972 | May 2 | October 8 | 158 days |
These are medians, not averages — NOAA publishes freeze dates as a probability distribution, and half of years freeze later than the date shown.
Your own ZIP
Work out your own dates
This page describes a whole county. Every tool below answers for one ZIP code, which is the grain the underlying data is published at.
Other places to compare
Merrimack County sits in New Hampshire. That page carries the whole state's zone spread, its metro areas, and every other county in it with a page here.
More of New Hampshire
- Cheshire County, NH 5b–6a
- Sullivan County, NH 5a–6a
- Coos County, NH 4a–5a
- Belknap County, NH 5b
- Grafton County, NH 4b–5b
- Carroll County, NH 5a–5b
Counties with the same zones — 5a–6a
Matched on the exact zone set, not a dominant zone, so the winter answer on these pages really is the same one as here.
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 5a 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 5a, 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
Hardiness zones are the USDA 2023 Plant Hardiness Zone Map, published per ZIP code by PRISM at Oregon State. Freeze dates and growing-season lengths are NOAA 1991–2020 Climate Normals, taken per station and cited above by name and NOAA ID.
County boundaries come from the Census ZCTA-to-county relation, which is what places each ZIP code — and which treats parishes, boroughs and census areas as county equivalents. No station is chosen to represent this county: every range above is taken across all of them and the count is stated, because picking one would be a judgement dressed as a measurement.