Generally — Most Areas
wild senna (zones 4-8) suits most of New Hampshire (3b-6b) — zones 4-6 are in range, and the rest of the state is the exception.
Wild Senna in New Hampshire — the short answer
Wild Senna in New Hampshire: hardy in zones 4–8, full sun.
- Plant zones
- 4-8
- Not verified — NC State Extension Gardener Plant Toolbox lists zones 4a–9b
- New Hampshire zones
- 3b-6b
- USDA PHZM 2023
- Frost window
- Apr 22 - May 4 – Oct 10 - Oct 21
- NOAA RCC ACIS 1991-2020, 28°F
- Shortest county season
- 145 days
- NOAA Regional Climate Centers ACIS, 1991-2020, county 28°F killing freeze
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS and university Extension sources — per-field provenance varies and is published with the dataset.
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 wild senna against your parcel's actual hardiness, soil, and sun.
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New Hampshire is not one climate
New Hampshire’s winter-low ladder runs across 10 counties, from zone 4.5 in Coos County to zone 6 in Strafford County. That is 15°F between the two counties’ average coldest night — the difference between wild senna overwintering in the ground and coming under cover.
The middle half of 10 counties runs 5–6 zones, with a median of 5.5 zones — a 1.5-zone span end to end.
Measured across 10 New Hampshire counties. USDA PHZM 2023, per county. Quartiles are order statistics — every figure shown is a value a real county recorded, not an interpolation. Your own site sits somewhere inside this range; a parcel report resolves where.
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 wild senna (USDA PHZM 2023):
Zone Comparison
Wild Senna Needs
- USDA Zones: 4-8
- Sun: Full SunWe haven't confirmed this against a published source yet.
- Mature size: 5 ft tallWe haven't confirmed this against a published source yet.
- Picking window: ~45 days of harvestWe haven't confirmed this against a published source yet.
- Drought tolerance: MediumWe haven't confirmed this against a published source yet.
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 4-8)
Preferred Soil pH
We haven't confirmed this against a published source yet.
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS, and university Extension sources — per-field provenance varies and is published with the dataset. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
When to Plant Wild Senna 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 wild senna, so this page does not state whether it overwinters here — and gives no fall establishment date on the strength of a guess. Whether wild senna 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: Growable Ground Plant Database — frost-free days from FAO ECOCROP, days to harvest from university Extension production guides, and growing-degree-day and chill-hour minimums that are compilation estimates rather than published figures. Your site's own frost dates can run earlier or later than the state range — a parcel report pins them down.
Soil + Drainage Fit
Wild Senna likes near-neutral soil (pH 5-7.5). That's the common-ground band across New Hampshire's glacial till and sandy loam — a soil test confirms it for your site. It will grow across that whole span, but it does best between pH 5.5 and 7 — worth knowing before you decide whether a New Hampshire soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your New Hampshire site is heavier clay or sits in a low spot, a raised bed lifts the roots above wet ground, or work in compost. pH range, preferred pH and drainage need: We haven't confirmed this against a published source yet.
Plant pH requirements: FAO ECOCROP and USDA PLANTS, with the remaining rows from other published sources or Growable Ground compilation. Drainage: FAO ECOCROP, with the remaining rows from other published sources or Growable Ground compilation. New Hampshire soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
What Else to Consider for Wild Senna 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 wild senna — is covered on the New Hampshire growing guide.
Where in New Hampshire Wild Senna Is Zone-Hardy
Wild Senna is rated for USDA zones 4–8. 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 wild senna 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". Wild Senna’s zone 4–8 band: Not verified — NC State Extension Gardener Plant Toolbox lists zones 4a–9b. A parcel report resolves your address’s own zone and frost dates rather than its county’s.
Pollinator + Wildlife Value
Wild Senna draws native bees. Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, wild senna 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. Pollinator value: We haven't confirmed this against a published source yet.
New Hampshire Cooperative Extension
For New Hampshire-specific cultivar recommendations, planting calendars, and pest pressure for wild senna, the canonical source is UNH Cooperative Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Wild Senna native to New Hampshire?
Yes — the USDA PLANTS Database (accessed 2026-10-19) records Wild Senna in New Hampshire, Kew's Plants of the World Online (WCVP) lists New Hampshire in its native range, and NatureServe Explorer's state data mark it native there. Planting it supports the pollinators and wildlife that evolved alongside it.
State records: USDA PLANTS Database state-distribution data (presence, not state-level nativity), accessed 2026-10-19.
Native-range status: Kew, Plants of the World Online — World Checklist of Vascular Plants (WCVP), release 2026-06-04, licensed CC BY 3.0. State native/exotic flags: NatureServe Explorer, CC BY, accessed 2026-10-19. powo.science.kew.org explorer.natureserve.org
Common Questions About Growing Wild Senna in New Hampshire
When can I plant Wild Senna 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 Wild Senna, 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 Wild Senna grown in across New Hampshire?
New Hampshire spans USDA hardiness zones 3b-6b (USDA ARS PHZM 2023). Wild Senna carries a range of zones 4-8, 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). Wild Senna needs 365+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date.
Is Wild Senna native to New Hampshire?
Yes — the USDA PLANTS Database (accessed 2026-10-19) records Wild Senna in New Hampshire, Kew's Plants of the World Online (WCVP) lists New Hampshire in its native range, and NatureServe Explorer's state data mark it native there. Planting it supports the pollinators and wildlife that evolved alongside it.
How should I amend the soil for Wild Senna in New Hampshire?
Wild Senna prefers pH 5-7.5 and well (dry spells) drainage. We haven't confirmed this against a published source yet. That sits in the common-ground band across New Hampshire soils — a 30-minute soil test from a local Extension lab confirms it for your specific site.
Will Wild Senna actually grow on my specific land in New Hampshire?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores wild senna against your address's mapped 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 wild senna against your land's mapped soil, modelled sun, drainage, and frost data — not zone averages.
Three things about your lot that New Hampshire wild senna averages can't show:
We read public map data around New Hampshire — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the New Hampshire wild senna average
Explore More
Growing guides for wild senna
Explore New Hampshire county by county
New Hampshire carries 10 counties with their own USDA zone — a sample of the growing pages for wild senna there:
Where else wild senna grows
Wild Senna's zone band crosses state lines — these are the states closest to New Hampshire in winter climate where it also has a page, plus the far ends of its range. Each one re-answers the question with that state's own record.
More to grow in New Hampshire
New Hampshire has a growing page for 807 plants — a rotating sample of the rest of the shelf.
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