Sunn Hemp is an annual grown for its pods, ready to pick about 90 days after sowing. It's hardy across USDA zones 7 through 11 and stands up to deer. Its indeterminate flowers are a moderate draw for honeybees, native bees, and butterflies, even though the pods are the prize. A nitrogen-fixer, it draws nitrogen from the air and feeds it back to the soil — turn it under or leave the roots in place, and the next planting inherits a richer bed.
Sunn Hemp — the short answer
Sunn Hemp: grown in zones 7–11, full sun, pH 5–8.4, about 90 days to maturity.
- USDA zones
- 7–11
- Manual horticultural correction (source not retained); NC State Extension and Missouri Botanical Garden, with the remaining rows from other published sources or Growable Ground compilation
- Soil pH
- 5–8.4
- FAO ECOCROP
- Sun
- Full Sun
- Growable Ground Plant Database
- Days to Maturity
- 90 days
- SARE
- Frost-kill temperature
- 30.2°F
- FAO ECOCROP
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS and university Extension sources — each tile names its own row's source, because per-field provenance varies.
Score Sunn Hemp on your exact land.
Zone averages can't see the slope, soil, frost, and sun that decide whether sunn hemp actually takes — and those shift from one yard to the next. Enter your address and we'll score sunn hemp against your land's real conditions.
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
What Sunn Hemp is
Sunn Hemp grows as an annual and reaches around six feet at maturity. It blooms yellow in indeterminate. It's also deer-resistant.
How to grow Sunn Hemp
Sunn Hemp grows in USDA zones 7 through 11 and is ready to harvest about 90 days after planting. Sunn Hemp does best in full sun — at least 6 hours of direct sun a day — and soil from pH 5 to 8.4, on well-drained ground. It needs around 2,200 growing degree days to mature and a growing season of at least 60 frost-free days, which is why climate matters as much as soil.
USDA Zones
7-11
USDA PHZM 2023
Soil pH
5 - 8.4
FAO ECOCROP
Sun
Full Sun
Growable Ground plant catalog
Drainage
well (dry spells)
Growable Ground plant catalog
Frost Kill Temperature
30.2°F
Where cold starts killing growing tissue. Not a winter-survival floor — a dormant perennial takes far colder, which its hardiness zone answers.
FAO ECOCROP
Minimum Growing Temperature
39.2°F
Below this it stops growing rather than dies — a pace limit, not a survival limit.
FAO ECOCROP
Days to Maturity
90 days
Sunn hemp; warm-season summer cover; nitrogen-fixing; tropical legume.
SARE
GDD Required
2200+
Growing degree-days of accumulated warmth it needs to mature — humid summers reach this faster than cool coastal ones.
Growable Ground plant catalog
Mature Height
6 ft
Growable Ground plant catalog
Frost-Free Days
60+
The frost-free stretch it needs start to finish — short-season areas may need an indoor head start.
Growable Ground plant catalog
Start the season right
Plant sunn hemp in full sun with at least 6 hours of direct sun, once the soil has warmed and frost risk has passed.
Match the soil
Sunn Hemp prefers pH 5 to 8.4 (FAO ECOCROP). A quick soil test from your local Extension lab tells you whether to add lime or sulfur to land in band. It fixes its own nitrogen, so skip the high-nitrogen feed and instead dust the seed with a matching rhizobium inoculant at sowing.
Water steadily
Keep the root zone evenly moist through establishment. A 2–3 inch mulch layer holds moisture without waterlogging.
Harvest at maturity
Sunn Hemp is ready about 90 days after sowing (SARE). Pick the pods young and tender, before the seeds inside fully swell.
Where Sunn Hemp thrives
Sunn Hemp is hardy across USDA zones 7 through 11. Zone is only the starting point, though: the soil pH, drainage, and frost dates on your specific land decide how well it actually does.
A USDA zone is a 10°F band of average annual extreme winter minimum, so zones 7–11 spans average winter lows from 0°F to 50°F (USDA PHZM 2023). Across the 50 states and DC, that band covers 7 outright and splits 34 more down the middle — and which side of that line your land sits on changes the answer.
Zones 7–11·Where Sunn Hemp growsOpen map →
Where Sunn Hemp stands, state by state
Sunn Hemp is rated for zones 7–11 — a cold floor USDA puts at 0 to 10°F. Across the 50 states and DC, 7 sit fully inside that band, the line runs through 34 more, and 10 sit outside it — and inside every split state, the same line runs on at county grain.
Fully inside zones 7–11
7 states
- Alabama · zones 7b-9b
- Delaware · zones 7a-8a
- District of Columbia · zones 7b-8a
3 of 7 shown
The line runs through
34 states
3 of 34 shown
Sunn Hemp’s band covers part of each of these states — which side of the line your county sits on changes the answer, and each state page draws it.
Outside zones 7–11
10 states
- Minnesota · zones 3a-5a
- Montana · zones 3a-6b
- New Hampshire · zones 3b-6b
3 of 10 shown
Winter cold is the limit here — the same plant often works in a container that comes under cover. Each link is that state’s own growing hub.
State zone extents: USDA Plant Hardiness Zone Map (PHZM) 2023. A zone is a 10°F band of average annual extreme minimum temperature, so a state that splits the band contains the boundary — its own page draws the county line, and a parcel report resolves which side your land sits on.
What grows around Sunn Hemp
Growing guides for sunn hemp
In rotation planning, sunn hemp counts as a Legume — beds recover best when legume crops don’t follow each other in the same spot year over year. (Growable Ground derivation — crop-rotation group from botanical family)
Good to know
One caution for pet owners — sunn hemp is toxic to dogs and cats (moderate severity). Keep it out of reach, and call ASPCA Animal Poison Control at (888) 426-4435 in an emergency. (Source: Cornell Poisonous Plants Database.)
Sunn Hemp offers moderate value to bees and other pollinators.
Your land is one point inside Sunn Hemp's range
This page resolves to the species. Your state page draws the county line, and a report reads the parcel — the soil pH, drainage, sun, and frost dates on your exact ground, which no species average can see.
See if Sunn Hemp will thrive on your land
Zone averages are a start. Your exact soil pH, drainage, sun exposure, and frost dates shape whether sunn hemp actually takes — we score it against the real conditions at your address.
Three things about your exact spot that zone averages miss:
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources analyzed in seconds
How we know this about Sunn Hemp
The figures above are cited per row, not per site: the pH band names this plant’s own source column, the three temperature figures each carry their own, and days-to-maturity cites the publication that actually lists it. All of it comes from the Growable Ground Plant Database — a compilation over FAO ECOCROP, USDA PLANTS, and university Extension sources, published openly with per-field provenance.
Grounded inUSDA PLANTS Database•USDA PHZM•ASPCA
Frequently asked questions
Can I grow Sunn Hemp in my zone?
Sunn Hemp grows in USDA hardiness zones 7 through 11 (USDA PHZM 2023). Zone is one factor — soil pH, drainage, and frost dates on your specific parcel also shape whether it takes.
How long does Sunn Hemp take to grow?
Sunn Hemp is ready to harvest about 90 days after planting (SARE). Your local frost dates and soil temperature move that window earlier or later.
When should you plant Sunn Hemp?
Most growers plant sunn hemp after the last spring frost, once the soil has warmed, leaving enough of the season for its 60-day frost-free need. Your local frost dates set the exact window — a Growable Ground report reads them for your address.
How much sun does Sunn Hemp need?
Sunn Hemp needs full sun — a spot that catches at least 6 hours of direct summer sun a day. In more shade it still grows, but usually gives a smaller, later crop. The catch is that a yard rarely gets even light everywhere — a fence, the house, or one tall tree can quietly take those hours. A Growable Ground report reads the real sun-hours across your land, canopy and buildings included, so you can pick the brightest bed before you plant.
What soil does Sunn Hemp need?
Sunn Hemp prefers soil pH 5 to 8.4, on well-drained ground (FAO ECOCROP). Your report scores your parcel's actual soil against that using USDA SSURGO data.
Does Sunn Hemp attract pollinators?
Yes — sunn hemp's flowers are a solid nectar source for honeybees, native bees, and butterflies.
Is Sunn Hemp safe for pets?
Sunn Hemp is toxic to pets (dogs,cats) with moderate severity. Keep it out of reach, and call ASPCA Animal Poison Control at (888) 426-4435 in an emergency. (Source: Cornell Poisonous Plants Database.)