Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated

Planting zone for 01860 — Merrimac, MA

ZIP code 01860 (Merrimac, Essex County) is in USDA zone 6a: the coldest winter night averages −10 to −5 °F. The median last spring frost is May 1 and the first fall frost October 12.

Where ZIP 01860 is

Outlined: the ZIP code area · tap the map for the zone at any spot · scroll or pinch to zoom

Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.

Zone6a−10 to −5 °F
Coldest night−23.3 to −20.6 °C
Last frostMay 1
First frostOct 12
2012 zone6a

Same zone as on the 2012 map. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 6a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Merrimac, MA…

Forecast data: National Weather Service (api.weather.gov), public domain. This is not a warning service — for official frost and freeze warnings see weather.gov.

Frost dates in Merrimac, MA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 1median — 50% chance of a later frost
Safe for tender plantsMay 14only 10% chance of frost after
First fall frostOctober 12median — 10% chance by Oct 1
Growing season163 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 19 and returns around October 23.

From the NOAA station Haverhill, MA — 6 miles away, elevation 20 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in 01860

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 20 – Apr 3
SpinachSow outdoors · Mar 20 – Apr 10
Broccoli, cabbageStart indoors · Feb 20 – Mar 6
Broccoli, cabbageTransplant · Apr 10 – Apr 24
Onion setsPlant outdoors · Apr 3 – Apr 17
PotatoesPlant outdoors · Apr 10 – Apr 24
LettuceSow outdoors · Apr 3 – Apr 17
Carrots, beetsSow outdoors · Apr 10 – Apr 24
TomatoesStart indoors · Mar 6 – Mar 20
TomatoesTransplant · May 8 – May 22
Peppers, eggplantStart indoors · Feb 20 – Mar 6
Peppers, eggplantTransplant · May 15 – May 29
BeansSow outdoors · May 8 – May 22
Sweet cornSow outdoors · May 8 – May 22
Cucumbers, squashSow outdoors · May 8 – May 22
Fall lettuce, spinachSow outdoors · Aug 17 – Aug 31
GarlicPlant cloves · Sep 28 – Nov 2
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 1) and first fall frost (Oct 12) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 01860 came on Apr 10 — about the same time as the 1991–2020 average (Apr 11).

JanFebMarAprMayJun

The Spring Index marks the day when accumulated warmth is enough for lilac and honeysuckle to leaf out — a widely used signal that the growing season has started. Source: USA National Phenology Network, www.usanpn.org — Spring Indices, first leaf, 2026 (data as of 2026-09-08) and 30-year average 1991–2020 (CC BY 4.0).

Native plants for zone 6a in Massachusetts

544 plants native to the lower 48 states, recorded in Massachusetts, and rated by the USDA to survive −10 °F or colder — the bottom of zone 6a. Each links to its USDA PLANTS profile.

Trees 66

American basswood100 ft · blooms late spring · low shade tolerance · to −46 °FAmerican beech80 ft · blooms mid spring · low shade tolerance · to −44 °FAmerican chestnut115 ft · blooms early summer · high shade tolerance · to −33 °FAmerican elm120 ft · blooms early spring · medium shade tolerance · to −46 °FAmerican sycamore100 ft · blooms spring · medium shade tolerance · to −34 °Farborvitae50 ft · blooms mid spring · medium shade tolerance · to −33 °F

Shrubs 109

alderleaf buckthorn3 ft · blooms late spring · low shade tolerance · to −33 °FAllegheny serviceberry35 ft · blooms early spring · low shade tolerance · to −38 °Falternateleaf dogwood25 ft · blooms mid spring · low shade tolerance · to −47 °FAmerican black currant3 ft · blooms early spring · to −46 °FAmerican hazelnut10 ft · blooms spring · medium shade tolerance · to −33 °FAmerican holly40 ft · blooms mid spring · low shade tolerance · to −20 °F

Wildflowers & perennials 186

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °FAmerican bur-reed3 ft · blooms indeterminate · medium shade tolerance · to −33 °FAmerican eelgrass1 ft · blooms mid summer · high shade tolerance · to −33 °FAmerican licorice4 ft · blooms late spring · medium shade tolerance · to −38 °FAmerican lotus3 ft · blooms mid summer · high shade tolerance · to −36 °FAmerican pokeweed7 ft · blooms mid summer · low shade tolerance · to −33 °F

Grasses 157

American beachgrass2.5 ft · blooms spring · high shade tolerance · to −28 °FAmerican cupscale3 ft · blooms early summer · high shade tolerance · to −18 °Farctic brome3 ft · blooms early summer · low shade tolerance · to −33 °Fawlfruit sedge4 ft · blooms mid spring · low shade tolerance · to −38 °FBailey's sedge2.1 ft · blooms late spring · low shade tolerance · to −33 °Fbeaked spikerush3 ft · blooms late spring · high shade tolerance · to −28 °F

Vines 8

American bittersweet15 ft · blooms spring · low shade tolerance · to −38 °Fdevil's darning needles15 ft · blooms mid summer · medium shade tolerance · to −38 °Ffrost grape83 ft · blooms late spring · medium shade tolerance · to −23 °Friverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °Fsummer grape30 ft · blooms late spring · low shade tolerance · to −23 °Ftrumpet creeper2 ft · blooms summer · high shade tolerance · to −13 °F

Source: USDA, NRCS. 2026. The PLANTS Database (plants.usda.gov), National Plant Data Team — state distribution, native status and the “Temperature, Minimum” characteristic. Check light, moisture and soil needs before buying; local nurseries and your state native plant society can confirm what thrives in Merrimac, MA.

Soil in Merrimac, MA

The soil mapped at the center of ZIP 01860 is Deerfield — loamy fine sand, moderately well drained.

TextureLoamy fine sanddrains and warms fast; dries out and needs more feeding
pH5.1strongly acidic; most vegetables like 6.0–7.0
DrainageModerately well drainednatural drainage class
Organic matter2.5%moderate
Hydrologic groupAwater soaks in fast
Farmland classFarmland of statewide importanceUSDA classification

Map unit: Deerfield loamy fine sand, 0 to 3 percent slopes.

Soil Survey Staff, Natural Resources Conservation Service, USDA. Soil Survey Geographic (SSURGO) Database, via Soil Data Access, accessed 2026-10-29. The soil at the center point of ZIP 01860; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Merrimac, MA

Summer high82 °Faverage high, July
Winter low16 °Faverage low, January
Hot days13days a year at 90 °F or more
Freezing nights143nights a year at 32 °F or less
Growing degree days2,524base 50 °F — the season’s usable heat
Longest day15 h 21 mindaylight on June 21
Shortest day9 h 01 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation47.4 inper year, rain and melted snow

Average high and low, by month

10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 35 °F, low 16 °F 35°16° JanFebruary: average high 38 °F, low 17 °F 38°17° FebMarch: average high 45 °F, low 24 °F 45°24° MarApril: average high 57 °F, low 34 °F 57°34° AprMay: average high 68 °F, low 45 °F 68°45° MayJune: average high 76 °F, low 54 °F 76°54° JunJuly: average high 82 °F, low 61 °F 82°61° JulAugust: average high 81 °F, low 59 °F 81°59° AugSeptember: average high 74 °F, low 51 °F 74°51° SepOctober: average high 62 °F, low 40 °F 62°40° OctNovember: average high 51 °F, low 31 °F 51°31° NovDecember: average high 40 °F, low 22 °F 40°22° Dec

Precipitation by month inches

0″1″2″3″4″5″January: 3.38 in precipitation 3.4 JanFebruary: 3.29 in precipitation 3.3 FebMarch: 4.33 in precipitation 4.3 MarApril: 4.21 in precipitation 4.2 AprMay: 3.72 in precipitation 3.7 MayJune: 4.26 in precipitation 4.3 JunJuly: 3.41 in precipitation 3.4 JulAugust: 3.70 in precipitation 3.7 AugSeptember: 3.98 in precipitation 4.0 SepOctober: 4.77 in precipitation 4.8 OctNovember: 3.80 in precipitation 3.8 NovDecember: 4.58 in precipitation 4.6 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Haverhill, MA (6 mi away); precipitation: Haverhill 0.7 N, MA (5 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

1 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

038596a
Newton Junction, NH · 2 mi
038586a
Newton, NH · 3 mi
019136a
Amesbury, MA · 3 mi
018306a
Haverhill, MA · 4 mi
019856b
West Newbury, MA · 4 mi
038656a
Plaistow, NH · 4 mi
038276a
East Kingston, NH · 5 mi
018346a
Groveland, MA · 6 mi

Massachusetts planting zones →

Questions about 01860

What planting zone is ZIP code 01860?

ZIP code 01860 (Merrimac, MA) is in USDA hardiness zone 6a on the 2023 map: the coldest night of an average winter reaches −10 to −5 °F (−23.3 to −20.6 °C).

When is the last frost in Merrimac, MA?

The median last spring frost (32 °F) near 01860 is May 1; after May 14 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Haverhill station.

When is the first frost in Merrimac, MA?

The median first fall frost near 01860 is October 12, giving a median frost-free growing season of 163 days.

When should I plant tomatoes in 01860?

Start tomato seeds indoors around Mar 6 – Mar 20 and set transplants outside around May 8 – May 22, one to three weeks after the median last frost.

How much rain and snow does 01860 get?

About 47.4 inches of precipitation a year (NOAA 1991–2020 normals, Haverhill 0.7 N station).

How hot do summers get in Merrimac, MA?

The average high peaks at 82 °F in July, with about 13 days a year at 90 °F or more.

What kind of soil does 01860 have?

The USDA soil survey maps Deerfield at the center of ZIP 01860: loamy fine sand, moderately well drained, pH about 5.1 (strongly acidic).

Did spring come early in Merrimac, MA in 2026?

Spring leaf-out near 01860 came on Apr 10 in 2026, about the same as the 1991–2020 average (Apr 11), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Merrimac, MA?

Long-day onions: the longest day near 01860 is 15 h 21 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).