Generally — Most Areas
knockout rose (zones 5-11) suits most of New Hampshire (3b-6b) — zones 5-6 are in range, and the rest of the state is the exception.
Your yard isn't the whole zone.
New Hampshire spans zones 3b-6b, but your yard sits in exactly one — and slope, tree cover, and cold-air pockets nudge it further. Enter your address and we'll score knockout rose against your parcel's actual hardiness, soil, and sun.
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Zone Comparison
Knockout Rose Needs
- USDA Zones: 5-11
- Sun: Part Sun
- Mature size: 4 ft tall
- Picking window: ~28 days of harvest
- Drought tolerance: Medium
New Hampshire Has
- USDA Zones: 3b-6b
- Last Hard Freeze (28°F): Apr 22 - May 4
- First Hard Freeze (28°F): Oct 10 - Oct 21
- Annual Rainfall: 36-50 inches
- Common Soils: Glacial till, Sandy loam, Rocky loam
Plant Zone Range (zones 5-11)
Plant data: USDA PLANTS Database / Growable Ground plant catalog. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
When to Plant Knockout Rose in New Hampshire
The frost window
Across New Hampshire, the last spring hard freeze (28°F) clears between Apr 22 and May 4, and the first fall hard freeze lands between Oct 10 and Oct 21 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 159-day window you can count on — up to 182 days on a mild site in a kind year. That marks the hard freeze, not the last light frost, so tender transplants usually wait another 2-3 weeks.
Winter standing
New Hampshire runs as cold as USDA zone 3, and no sourced winter-hardiness floor is on record for knockout rose, so this page does not state whether it overwinters here — and gives no fall establishment date on the strength of a guess. Whether knockout rose is a permanent planting or a replant-every-spring crop for you turns on your own zone within New Hampshire; check its hardiness range against that before treating it as long-lived ground.
Frost window: NOAA Climate Normals 1991-2020. Plant timing fields: USDA PLANTS Database. Your site's own frost dates can run earlier or later than the state range — a parcel report pins them down.
Growing Season Fit
The zone check says knockout rose survives winter in part of New Hampshire, not across all of it. Whether the season is long enough — and warm enough — is a different question.
Chill hours
Knockout Rose requires ~200 chill hours (32-45°F dormancy window). New Hampshire typically banks ~2500 chill hours per winter (from PRISM 1991-2020 climate normals), which keeps this plant on track.
GDD and chill-hour figures are computed from PRISM 1991-2020 monthly climate normals; frost-free days from NOAA Regional Climate Centers ACIS, 1991-2020. Each is the state median across its counties (P25/P75 span the within-state spread). Hardiness-zone range is USDA PHZM 2023.
Soil + Drainage Fit
Drainage matters: this plant wants well (dry spells). If your New Hampshire site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
Plant pH and drainage requirements from USDA PLANTS Database. New Hampshire soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Knockout Rose in New Hampshire — Quick Answer
- Verdict: Generally — Most Areas
- Plant Zones: 5-11 (USDA PLANTS Database)
- State Zones: 3b-6b (USDA ARS PHZM 2023)
- Growing Season: 28°F hard freezes about Apr 22 - May 4 to Oct 10 - Oct 21 (NOAA Regional Climate Centers ACIS, 1991-2020)
What Else to Consider for Knockout Rose in New Hampshire
Zone compatibility tells you about winter cold survival — but New Hampshire growers also need to think about:
Very short season in the White Mountains (80-100 frost-free days)
Rocky glacial soils throughout the state
Harsh winters with deep snow cover
What to actually do about these — and the constraints that apply to every New Hampshire grower, not just knockout rose — is covered on the New Hampshire growing guide.
Where in New Hampshire Knockout Rose Is Zone-Hardy
Knockout Rose is rated for USDA zones 5–11. 9 of New Hampshire’s 10 counties fall inside that band. The coldest that does is Carroll County at zone 5a. 1 county sits below the plant’s zone 5 floor, where an unprotected plant is relying on snow cover and a mild year. Where you are in New Hampshire decides this one.
Across those 10 counties New Hampshire’s winter-low ladder runs from zone 4b in Coos County to zone 6a in Strafford County — 1.5 USDA zones of spread, which is 15°F between the two counties’ average coldest night of the year. That is why a statewide hardiness answer is where you start and not where you finish.
The planting window moves with it. Coos County holds its last hard freeze (28°F) until about May 13, while Rockingham County is clear by Apr 17 — 26 days apart. Set knockout rose out on your county’s date, not the state’s.
County hardiness zones: USDA Plant Hardiness Zone Map (PHZM) 2023, per county. County last-freeze dates: NOAA Regional Climate Centers ACIS (1991-2020), county 28°F killing freeze — earlier than the folk 32°F "last frost". Knockout Rose’s zone 5–11 band: USDA PLANTS / Growable Ground plant database. A parcel report resolves your address’s own zone and frost dates rather than its county’s.
Where in New Hampshire Fits Best
Even within New Hampshire's zones 3b-6b, county microclimates differ enough to change what thrives. These counties carry the closest zone match for knockout rose (USDA PHZM 2023):
Pollinator + Wildlife Value
Knockout Rose draws honeybees and native bees (moderate value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, knockout rose can only work that bloom inside New Hampshire's frost window — roughly 171 days, opening after the last 28°F freeze (Apr 22 - May 4) and closing at the first (Oct 10 - Oct 21), per NOAA Regional Climate Centers ACIS, 1991-2020.
New Hampshire Cooperative Extension
For New Hampshire-specific cultivar recommendations, planting calendars, and pest pressure for knockout rose, the canonical source is UNH Cooperative Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
What pests threaten knockout rose in New Hampshire?
Japanese beetle is documented in New Hampshire, and it hits knockout rose where it counts. Here is what it actually does — and the move that beats it.
Japanese beetle
Act on thisRose is at the top of the Japanese beetle's preferred-plant list, and it is the one case where 'cosmetic' misses the point: the University of Minnesota notes healthy roses survive the feeding, but the blossoms are often ruined — the thing you grow the plant for.
What to do: Handpick or knock beetles into a bucket of soapy water, daily, in the cool of morning or evening — damaged leaves release an odor that pulls in more beetles, so removing them lowers next week's numbers. Handpick while the plant is in bloom, then net it once flowering is done. Skip the pheromone traps: University of Kentucky research found they draw in more beetles than they catch.
Documented range: states listed as Japanese-beetle infested · University of Minnesota Extension, National Plant Board
Only pests whose documented range and host relationship both trace to a primary source appear here — so a quiet section means we have nothing sourced to tell you, not that your garden is pest-free.
Common Questions About Growing Knockout Rose in New Hampshire
When can I plant Knockout Rose in New Hampshire?
New Hampshire's last spring hard freeze (28°F) clears between Apr 22 and May 4, and the first fall hard freeze lands between Oct 10 and Oct 21 (NOAA Regional Climate Centers ACIS, 1991-2020). No sourced winter-hardiness floor is on record for Knockout Rose, so this page does not state whether it overwinters in New Hampshire and publishes no fall establishment date for it — check its hardiness range against your own zone before treating it as a permanent planting.
What hardiness zone is Knockout Rose grown in across New Hampshire?
New Hampshire spans USDA hardiness zones 3b-6b (USDA ARS PHZM 2023). Knockout Rose carries a range of zones 5-11, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical New Hampshire site have?
A typical New Hampshire site sees ~171 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Knockout Rose should be matched against that window, so check whether your local microclimate runs above or below the state average before settling on a planting date.
Will Knockout Rose actually grow on my specific land in New Hampshire?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores knockout rose against your address's exact soil pH, drainage, sun, and frost-date data drawn from USDA SSURGO, NOAA, and PRISM — not state averages.
Check your specific parcel in New Hampshire
State-level data is a sketch. Your Growable Ground report scores knockout rose against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that New Hampshire knockout rose averages can't show:
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