Generally — Most Areas
blue lobelia (zones 4-9) suits most of New Hampshire (3b-6b) — zones 4-6 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 blue lobelia against your parcel's actual hardiness, soil, and sun.
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Zone Comparison
Blue Lobelia Needs
- USDA Zones: 4-9
- Mature size: 3 ft tall
- Picking window: ~30 days of harvest
- Drought tolerance: Low
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 4-9)
Plant data: USDA PLANTS Database / Growable Ground plant catalog. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
When to Plant Blue Lobelia 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 blue lobelia, so this page does not state whether it overwinters here — and gives no fall establishment date on the strength of a guess. Whether blue lobelia 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.
Blue Lobelia in New Hampshire — Quick Answer
- Verdict: Generally — Most Areas
- Plant Zones: 4-9 (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 Blue Lobelia 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 blue lobelia — is covered on the New Hampshire growing guide.
Where in New Hampshire Blue Lobelia Is Zone-Hardy
Blue Lobelia is rated for USDA zones 4–9. Every one of New Hampshire’s 10 counties sits inside that band — from Coos County at zone 4b to Strafford County at zone 6a — so winter cold is not what decides this plant anywhere in the state. What is left to vary is your own parcel: slope, shelter and cold-air drainage routinely move a site half a zone either way from the county figure.
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 blue lobelia 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". Blue Lobelia’s zone 4–9 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 blue lobelia (USDA PHZM 2023):
Pollinator + Wildlife Value
Blue Lobelia draws native bees, butterflies, and hummingbirds (high value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, blue lobelia 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 blue lobelia, the canonical source is UNH Cooperative Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Blue Lobelia native to New Hampshire?
Yes — the USDA PLANTS Database (accessed 2026-07-01) documents Blue Lobelia as native to New Hampshire. Planting it supports the pollinators and wildlife that evolved alongside it.
Native-range data: USDA PLANTS Database state-distribution records, accessed 2026-07-01.
Common Questions About Growing Blue Lobelia in New Hampshire
When can I plant Blue Lobelia 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 Blue Lobelia, 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 Blue Lobelia grown in across New Hampshire?
New Hampshire spans USDA hardiness zones 3b-6b (USDA ARS PHZM 2023). Blue Lobelia carries a range of zones 4-9, 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). Blue Lobelia 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.
Is Blue Lobelia native to New Hampshire?
Yes — the USDA PLANTS Database (accessed 2026-07-01) documents Blue Lobelia as native to New Hampshire. Planting it supports the pollinators and wildlife that evolved alongside it.
Will Blue Lobelia actually grow on my specific land in New Hampshire?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores blue lobelia 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 blue lobelia against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that New Hampshire blue lobelia averages can't show:
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Growing guides for blue lobelia
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