Southern New Hampshire contains 2 USDA planting zones: 5b and 6a, based on the 2023 USDA Hardiness Zone Map update. Zone 5b experiences winter minimums of -15°F to -10°F (-26.1°C to -23.3°C), and zone 6a experiences -10°F to -5°F (-23.3°C to -20.6°C).
Zone 5b covers western Manchester sections and western Hillsborough County areas with elevations exceeding 1,000 feet. Zone 6a includes Nashua, Hudson, Amherst, Goffstown, and Hooksett entirely, plus eastern Manchester sections. Manchester spans both zones due to elevation variations from 175 feet to 610 feet across the city.
The Merrimack River valley creates temperature-moderating microclimates, raising winter temperatures 3-5°F above surrounding highlands through Manchester and Nashua. These river corridor effects explain why most southern New Hampshire towns are in zone 6a designation.
USDA Zones Map of Southern New Hampshire
Select or type your Southern New Hampshire city or town in selection box below, to find its USDA Growing zone.
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USDA Planting Zone
This zone’s data comes from the United States Department of Agriculture (USDA), with the most recent zone updates released in 2023
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Planting Zones Table of Southern NH
The table below lists all the cities and towns in Southern NH along with thier USDA Hardniess zones.
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What Are the 2 Primary USDA Hardiness Zones in Southern New Hampshire Towns?
Zone 5b and zone 6a are the 2 primary USDA hardiness zones in Southern New Hampshire towns. Manchester contains zone 5b in western sections, Amherst maintains zone 6a throughout, Goffstown experiences zone 6a conditions, Hillsborough County spans zones 5b-6a, Hooksett remains zone 6a, Hudson maintains zone 6a, and Nashua experiences zone 6a temperatures.
1. Zone 5b in Western Manchester
Western Manchester experiences -15°F to -10°F (-26.1°C to -23.3°C) winter minimums in zone 5b. Western Manchester’s higher elevations of 400-610 feet create colder conditions compared to eastern sections at 175-300 feet elevation.
Manchester’s concrete infrastructure raises temperatures 2-3°F through urban heat island effects. Western sections remain zone 5b despite urban warming because northwest wind exposure at higher elevations counteracts heat retention.
Sugar maples (Acer saccharum), white pines (Pinus strobus), and northern red oaks (Quercus rubra) thrive in zone 5b Manchester. These 3 species tolerate -15°F minimums and adapt to Manchester’s urban-influenced climate conditions.
2. Zone 6a in Amherst
Zone 6a in Amherst experiences -10°F to -5°F (-23.3°C to -20.6°C) average annual extreme minimum winter temperatures. Amherst’s elevation of 269 feet and southern Hillsborough County positioning create 5°F warmer conditions than northern New Hampshire towns.
Southern exposure shields Amherst from mountain cold air masses. The town’s rolling terrain at 200-400 feet elevation avoids cold air drainage common in valleys.
Eastern redbuds (Cercis canadensis), Japanese maples (Acer palmatum), and American hollies (Ilex opaca) flourish in zone 6a Amherst. These 3 species require temperatures above -10°F for winter survival.
3. Zone 6a in Goffstown
Goffstown experiences -10°F to -5°F (-23.3°C to -20.6°C) winter minimums in zone 6a. Goffstown’s position along the Merrimack River corridor provides thermal moderation from the river’s 500 million gallon daily flow.
The Merrimack River’s thermal mass prevents extreme temperature drops, maintaining 3-4°F warmer winter conditions than nearby hills. Goffstown’s elevation range of 250-800 feet creates microclimates, with river areas staying warmest.
Tulip trees (Liriodendron tulipifera), sweetgums (Liquidambar styraciflua), and flowering dogwoods (Cornus florida) grow successfully in zone 6a Goffstown. River proximity extends growing seasons 10-14 days beyond inland locations.
4. Zones 5b and 6a in Hillsborough County
Hillsborough County contains both zone 5b and zone 6a across its 876 square miles, with zone boundaries determined by elevation and river proximity. Zone 5b covers western sections above 1,000 feet elevation, while zone 6a encompasses eastern lowlands below 500 feet.
The county’s topographical diversity ranges from 175 feet along the Merrimack River to 2,290 feet at Pack Monadnock Mountain. This 2,115-foot elevation difference creates 10-15°F temperature variations across the county during winter months.
Zone transitions occur at 600-800 feet elevation, where temperature gradients shift from zone 6a to zone 5b conditions. Western towns like Antrim and Hillsborough experience zone 5b conditions, and eastern communities maintain zone 6a temperatures.
5. Zone 6a in Hooksett
Hooksett maintains -10°F to -5°F** (-23.3°C to -20.6°C) winter minimums in zone 6a. The town’s 320-foot elevation within Merrimack River corridor ensures consistent zone 6a temperatures.
The Merrimack River’s southward flow through Hooksett carries thermal energy from upstream sources, preventing extreme cold air settlement. Hooksett’s river frontage spans 8 miles, maximizing moderating effects on local climate.
American elms (Ulmus americana), Red maples (Acer rubrum), and White ashes (Fraxinus americana) thrive in zone 6a Hooksett. River valley protection extends frost-free periods 7-10 days beyond highland areas.
6. Zone 6a in Hudson
Hudson experiences -10°F to -5°F** (-23.3°C to -20.6°C) winter minimums throughout zone 6a. Hudson’s position along New Hampshire’s Massachusetts border provides 3-5°F warmer winter temperatures compared to northern New Hampshire locations.
Hudson’s latitude of 42.7°N matches central Massachusetts climate patterns, receiving moderating influences from southern weather systems. The town’s elevation of 200-400 feet avoids cold air drainage while benefiting from southern exposure.
Southern magnolias (Magnolia grandiflora), American beeches (Fagus grandifolia), and black walnuts (Juglans nigra) grow in zone 6a Hudson.
7. Zone 6a in Nashua
Nashua maintains -10°F to -5°F** (-23.3°C to -20.6°C) winter minimums in zone 6a. The city combines urban heat effects with river moderation for optimal growing conditions.
Nashua’s urban heat island effect raises temperatures 2-4°F above rural surroundings, while Merrimack River proximity provides additional thermal stability. The city’s latitude of 42.7°N delivers 15-20 days longer growing seasons compared to northern New Hampshire.
London planetrees (Platanus × acerifolia), Japanese zelkovas (Zelkova serrata), and Korean dogwoods (Cornus kousa) flourish in zone 6a Nashua.
How Do Geography Influences Southern New Hampshire Climate Zones?
Elevation, river proximity, and latitude shape Southern New Hampshire climate zones. The region experiences 80-85°F summer temperatures and 40-60 inches annual snowfall in humid continental conditions.
Elevation Effects on Zone Distribution
Elevation changes of 500-1,000 feet produce 5-10°F temperature differences across Southern New Hampshire, according to National Weather Service climate data. Zone boundaries shift from 6a to 5b at approximately 600-800 feet elevation, where cold air drainage and wind exposure intensify.
Western areas above 1,000 feet experience zone 5b conditions. Eastern lowlands below 500 feet maintain zone 6a temperatures. Temperature decreases follow the 3.5°F per 1,000 feet environmental lapse rate.
River Valley Moderation
The Merrimack River valley maintains temperatures 3-5°F warmer than surrounding highlands through thermal mass effects. The river’s 500 million gallon daily flow carries thermal energy downstream, preventing extreme cold air settlement in valley communities.
Manchester, Nashua, Goffstown, and Hooksett benefit from river moderation, maintaining zone 6a despite northern latitude positioning. Water temperature remains 35-40°F during winter months, moderating adjacent air temperatures.
Climate Zone Transition Trends
Southern New Hampshire transitioned to warmer zones between 2012-2023, according to USDA Plant Hardiness Zone Map updates. Areas previously experiencing -15°F minimums now record -10°F minimums, representing a 5°F warming trend over the 11-year period.
Multiple locations transitioned from zone 5b to zone 6a classification. This warming expands plant variety options for gardeners by 30-40 percent. Regional data confirms 1-2°F temperature increases per decade across New England.
What Plants Thrive in Southern New Hampshire’s Zone 5b and Zone 6a?
Plants thriving in Southern New Hampshire’s zones include cold-hardy species for zone 5b and expanded variety options for zone 6a. Zone 5b supports traditional New England species like sugar maples, white pines, and northern red oaks. Zone 6a supports these species plus marginally hardy varieties like Eastern redbuds, Japanese maples, and flowering dogwoods.
Zone 5b Plants
Zone 5b plants must tolerate -15°F winter minimums, limiting selections to extremely cold-hardy species. Trees include sugar maples, white pines, northern red oaks, and paper birches.
Shrubs for zone 5b include common lilacs, forsythias, and viburnums. Perennials include hostas, daylilies, and purple coneflowers.
Zone 6a Plants
Zone 6a’s -10°F minimum temperatures expand plant options by 30-40% compared to zone 5b selections. Additional trees for this zone include Eastern redbuds, tulip trees, and American hollies.
Zone 6a shrubs include Japanese maples, Korean dogwoods, and oakleaf hydrangeas. Extended perennials plants for zone 6a include coral bells, Japanese painted ferns, and astilbes.