Unlikely — Zone Mismatch
horse gram (zones 8-12) does not overlap with Iowa's zone range (4b-6a). Growing outdoors is unlikely without significant protection.
2 zones short — what would close it
Horse Gram is hardy to zone 8, and the warmest ground in Iowa is zone 6 — 2 zones short. Planted in open ground it will not survive a Iowa winter. To grow it here, grow horse gram under glass — a greenhouse is the only lift this wide the engine models.
A greenhouse is the lift this needs. How a greenhouse changes what you can grow →
Zone math from 8-12 (plant) against 4-6 (Iowa). Lift modeled by crop_engine Sprint 20B effective_zone_modifier (+2 zones) via api/fast_sections.py Unlock Engine v2.
Your yard isn't the whole zone.
Iowa spans zones 4b-6a, but your yard has its own microclimate — slope, trees, and low spots shift frost and sun across a single parcel. Enter your address and we'll score horse gram against your land's actual soil, sun, and frost.
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Zone Comparison
Horse Gram Needs
- USDA Zones: 8-12
- Frost-Free Days: 40+
- Sun: Full Sun
- Mature size: 2 ft tall
- Picking window: ~14 days of harvest
- Drought tolerance: High
Iowa Has
- USDA Zones: 4b-6a
- Last Hard Freeze (28°F): Apr 10 - Apr 17
- First Hard Freeze (28°F): Oct 18 - Oct 23
- Annual Rainfall: 26-36 inches
- Common Soils: Prairie loess, Silt loam, Clay loam
Plant Zone Range (zones 8-12)
Preferred Soil pH
Plant data: USDA PLANTS Database / Growable Ground plant catalog. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
When to Plant Horse Gram in Iowa
The frost window
Across Iowa, the last spring hard freeze (28°F) clears between Apr 10 and Apr 17, and the first fall hard freeze lands between Oct 18 and Oct 23 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 184-day window you can count on — up to 196 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.
Frost tenderness
Horse Gram is frost-tender — its listed minimum temperature is 62.6°F (USDA PLANTS Database) — so set plants out two to three weeks PAST your local last hard freeze, not on it and not on the state's earliest date. The 28°F marker above is when killing freezes stop, not when light frost does.
When to start the seed
Horse Gram is direct-sown where it grows rather than started under cover, so there is no seed-tray head start to bank — Iowa's dates above are the whole calendar for it. That makes the last-freeze date the binding constraint, and a warmer pocket of your own yard is worth more to this crop than it is to a transplanted one.
Days to maturity vs. the window
At 120 days to maturity (USDA PLANTS Database), counting from the last hard freeze it ripens with 64 days to spare even in Iowa's tightest freeze scenario — room for a later start or a second sowing.
Timing tuned to sub-state frost dates — Howard County, not the statewide average.
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 horse gram does not survive a Iowa winter in the ground. The season figures below measure a different question — whether it could finish a season here at all — and they only bear on Iowa under protection.
Frost-free days
Horse Gram wants 40+ frost-free days; a typical Iowa site sees ~189 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves comfortable headroom for succession planting.
Growing degree days
Horse Gram needs ~2500 GDD (base 50°F) to ripen. The state median runs ~2730 GDD (from PRISM 1991-2020 climate normals), so Iowa sits right at the threshold — pay attention to siting and microclimate.
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
Horse Gram tolerates a wide pH range (pH 5-8) — 3 units, acid ground through alkaline — so soil acidity is rarely what limits it in Iowa. A soil test is still worth having, but for what else it tells you about this site, not to clear this plant. It will grow across that whole span, but it does best between pH 5.5 and 7 — worth knowing before you decide whether a Iowa soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your Iowa site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
Your land, not the state average
SSURGO maps about 42.9% of Iowa as poorly or somewhat-poorly drained, and the class flips parcel to parcel. Horse Gram tolerates drought well, so wet feet — not dry spells — is its real risk here — your soil map unit, not the state average, is the real answer.
Check your parcel → Source: USDA NRCS SSURGO.
Plant pH and drainage requirements from USDA PLANTS Database. Iowa soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Horse Gram in Iowa — Quick Answer
- Verdict: Unlikely — Zone Mismatch
- Plant Zones: 8-12 (USDA PLANTS Database)
- State Zones: 4b-6a (USDA ARS PHZM 2023)
- Growing Season: 28°F hard freezes about Apr 10 - Apr 17 to Oct 18 - Oct 23 (NOAA Regional Climate Centers ACIS, 1991-2020)
- Days to Maturity: 120 days
What Else to Consider for Horse Gram in Iowa
Zone compatibility tells you about winter cold survival — but Iowa growers also need to think about:
Cold winters reaching -20F or below
Variable spring weather delays planting
Wind exposure on open prairies desiccates plants
Growing horse gram here specifically
Horse Gram rates to USDA zones 8–12 and is hardy to about 62°F, but cold isn't the risk in Iowa — wet is: with roughly 42.9% of its soils poorly-drained (SSURGO), soggy ground rots the roots.
Give horse gram a raised bed or mounded row with coarse amendment so its roots never sit wet. How to handle it →
What to actually do about these — and the constraints that apply to every Iowa grower, not just horse gram — is covered on the Iowa growing guide.
Timing shifts within Iowa
Iowa isn't one climate. In Howard County, the last hard freeze (28°F) holds until about Apr 24 — roughly 10 days later than the recorded state median — so plant horse gram to your county's window, not the statewide date.
Horse Gram needs about 40 days of frost-free season to complete its cycle. Even Howard County — Iowa’s shortest season at 168 frost-free days — clears that by 128 days, so season length isn’t the constraint anywhere in Iowa. What varies is your own parcel.
County last-freeze dates and frost-free day counts: NOAA Regional Climate Centers ACIS (1991-2020), county 28°F freeze (earlier than the folk 32°F "last frost"). Horse Gram's 40-day requirement: USDA PLANTS / Growable Ground plant database (minimum frost-free days). A parcel report resolves your address's own frost dates.
Pollinator + Wildlife Value
Horse Gram draws honeybees (low value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, horse gram can only work that bloom inside Iowa's frost window — roughly 189 days, opening after the last 28°F freeze (Apr 10 - Apr 17) and closing at the first (Oct 18 - Oct 23), per NOAA Regional Climate Centers ACIS, 1991-2020.
Iowa Cooperative Extension
For Iowa-specific cultivar recommendations, planting calendars, and pest pressure for horse gram, the canonical source is Iowa State University Extension and Outreach. Their fact sheets carry the local trial data we can't generalize across 50 states.
Common Questions About Growing Horse Gram in Iowa
When can I plant Horse Gram in Iowa?
Iowa's last spring hard freeze (28°F) clears between Apr 10 and Apr 17, and the first fall hard freeze lands between Oct 18 and Oct 23 (NOAA Regional Climate Centers ACIS, 1991-2020). Horse Gram is frost-tender — its listed minimum temperature is 62.6°F (USDA PLANTS Database) — so wait two to three weeks past your site's last hard freeze, when light frost has also stopped, before planting out.
Can Horse Gram mature before first frost in Iowa?
Yes — Horse Gram matures in 120 days (USDA PLANTS Database), and Iowa's dependable hard-freeze-free window runs 184 days (NOAA Regional Climate Centers ACIS, 1991-2020), leaving 64 days of margin. Plant once the last hard freeze has passed — two to three weeks later for anything tender — and it ripens ahead of the first fall freeze.
What hardiness zone is Horse Gram grown in across Iowa?
Iowa spans USDA hardiness zones 4b-6a (USDA ARS PHZM 2023). Horse Gram carries a range of zones 8-12, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical Iowa site have?
A typical Iowa site sees ~189 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Horse Gram needs 40+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date. In cooler counties like Howard, the freeze-free season runs shorter than the state average, so verify your own county's window.
How should I amend the soil for Horse Gram in Iowa?
Horse Gram tolerates pH 5-8 and well (dry spells) drainage (FAO ECOCROP). That is a 3-unit span, acid ground through alkaline, so pH is rarely what limits this plant on a Iowa site — amend for drainage and organic matter first.
Will Horse Gram actually grow on my specific land in Iowa?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores horse gram 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 Iowa
State-level data is a sketch. Your Growable Ground report scores horse gram against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Iowa horse gram averages can't show:
We read public map data around Iowa — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Iowa horse gram average
Explore More
Growing guides for horse gram
Analysis by the Growable Ground research team, grounded in USDA PLANTS, USDA NRCS SSURGO, NOAA Climate Normals (1991-2020), and named Cooperative Extension sources. How we know →
Cite this dataset
Kirchick, M. (2026). Growable Ground Plant Database [Data set]. Zenodo. https://doi.org/10.5281/zenodo.21435643
Licensed CC BY-NC 4.0. DOI 10.5281/zenodo.21435643
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