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 heavy 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.
Zones
7-11
pH Range
5-8.4
Sun
Full Sun
Days to Maturity
90
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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
USDA PLANTS Database
Sun
Full Sun
plant_species_v5.csv
Drainage
well (dry spells)
plant_species_v5.csv
Frost Tolerance
39.2°F
plant_species_v5.csv
Days to Maturity
90 days
Sunn hemp; warm-season summer cover; nitrogen-fixing; tropical legume.
SARE
GDD Required
2200+
plant_species_v5.csv
Mature Height
6 ft
plant_species_v5.csv
Frost-Free Days
60+
plant_species_v5.csv
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 (USDA PLANTS Database). 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.
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: ASPCA.)
Sunn Hemp offers moderate value to bees and other pollinators. (Source: Xerces Society, Pollinator Partnership.)
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.
Zones 7–11·Where Sunn Hemp growsOpen map →
On USDA hardiness-zone overlap, Sunn Hemp can grow in these states:
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.
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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 (USDA PLANTS Database). 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 (Xerces Society, Pollinator Partnership).
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.