Unlikely — Zone Mismatch
calopo (zones 10-12) does not overlap with Arkansas's zone range (6b-8b). Growing outdoors is unlikely without significant protection.
2 zones short — what would close it
Calopo is hardy to zone 10, and the warmest ground in Arkansas is zone 8 — 2 zones short. Planted in open ground it will not survive a Arkansas winter. To grow it here, grow calopo 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 10-12 (plant) against 6-8 (Arkansas). 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.
Calopo is grown as an annual, so your winter zone isn't the deciding factor — your frost-free window is. A typical Arkansas site runs ~254 frost-free days, but that is a state median, not your yard: slope, trees, and low spots move the last-frost date across a single parcel. Enter your address and we'll score calopo against your land's actual frost dates, sun, and soil.
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Zone Comparison
Calopo Needs
- USDA Zones: 10-12
- Frost-Free Days: 120+
- Sun: Full Sun
- Mature size: 1 ft tall
- Drought tolerance: Low
Arkansas Has
- USDA Zones: 6b-8b
- Last Hard Freeze (28°F): Mar 2 - Mar 20
- First Hard Freeze (28°F): Nov 15 - Nov 23
- Annual Rainfall: 44-56 inches
- Common Soils: Silt loam, Sandy loam, Red clay
Plant Zone Range (zones 10-12)
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 Calopo in Arkansas
The frost window
Across Arkansas, the last spring hard freeze (28°F) clears between Mar 2 and Mar 20, and the first fall hard freeze lands between Nov 15 and Nov 23 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 240-day window you can count on — up to 266 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
Calopo is frost-tender — its listed minimum temperature is 64.4°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.
Timing tuned to sub-state frost dates — Carroll 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 calopo does not survive a Arkansas 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 Arkansas under protection.
Frost-free days
Calopo wants 120+ frost-free days; a typical Arkansas site sees ~254 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves comfortable headroom for succession planting.
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
Calopo tolerates a wide pH range (pH 4.3-8) — 3.7 units, acid ground through alkaline — so soil acidity is rarely what limits it in Arkansas. 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 4.5 and 5.7 — worth knowing before you decide whether a Arkansas soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your Arkansas 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 33.9% of Arkansas as poorly or somewhat-poorly drained, and the class flips parcel to parcel. Calopo has low drought tolerance, so it is the fast-draining end that will cost you — 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. Arkansas soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Calopo in Arkansas — Quick Answer
- Verdict: Unlikely — Zone Mismatch
- Plant Zones: 10-12 (USDA PLANTS Database)
- State Zones: 6b-8b (USDA ARS PHZM 2023)
- Growing Season: 28°F hard freezes about Mar 2 - Mar 20 to Nov 15 - Nov 23 (NOAA Regional Climate Centers ACIS, 1991-2020)
What Else to Consider for Calopo in Arkansas
Zone compatibility tells you about winter cold survival — but Arkansas growers also need to think about:
Hot, humid summers drive fungal and bacterial diseases
Heavy clay soils in parts of the Ozarks
Severe spring storms and hail risk
Growing calopo here specifically
Calopo likes pH 4.3–8.0 and takes cold to about 64°F, yet neither saves it from wet feet — SSURGO maps about 33.9% of Arkansas poorly-drained, where its roots sit and rot.
Set calopo high on bermed, grit-amended ground so winter and storm water drain away from the roots. How to handle it →
What to actually do about these — and the constraints that apply to every Arkansas grower, not just calopo — is covered on the Arkansas growing guide.
Timing shifts within Arkansas
Arkansas isn't one climate. In Carroll County, the last hard freeze (28°F) holds until about Mar 26 — roughly 16 days later than the recorded state median — so plant calopo to your county's window, not the statewide date.
Calopo needs about 120 days of frost-free season to complete its cycle. Even Benton County — Arkansas’s shortest season at 226 frost-free days — clears that by 106 days, so season length isn’t the constraint anywhere in Arkansas. 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"). Calopo's 120-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
Calopo draws honeybees (low value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, calopo can only work that bloom inside Arkansas's frost window — roughly 254 days, opening after the last 28°F freeze (Mar 2 - Mar 20) and closing at the first (Nov 15 - Nov 23), per NOAA Regional Climate Centers ACIS, 1991-2020.
Arkansas Cooperative Extension
For Arkansas-specific cultivar recommendations, planting calendars, and pest pressure for calopo, the canonical source is University of Arkansas Cooperative Extension Service. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Calopo native to Arkansas?
No — the USDA PLANTS Database lists Calopo as introduced rather than native in the Lower 48, so it is not part of Arkansas's native flora. It grows here as a garden plant; pairing it with a few Arkansas natives keeps local pollinators fed too.
Looking for plants that belong here? The Arkansas growing guide lists USDA-documented natives for the state.
Native-range data: USDA PLANTS Database state-distribution records, accessed 2026-07-01.
Common Questions About Growing Calopo in Arkansas
When can I plant Calopo in Arkansas?
Arkansas's last spring hard freeze (28°F) clears between Mar 2 and Mar 20, and the first fall hard freeze lands between Nov 15 and Nov 23 (NOAA Regional Climate Centers ACIS, 1991-2020). Calopo is frost-tender — its listed minimum temperature is 64.4°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.
What hardiness zone is Calopo grown in across Arkansas?
Arkansas spans USDA hardiness zones 6b-8b (USDA ARS PHZM 2023). Calopo carries a range of zones 10-12, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical Arkansas site have?
A typical Arkansas site sees ~254 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Calopo needs 120+ 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 Carroll, the freeze-free season runs shorter than the state average, so verify your own county's window.
Is Calopo native to Arkansas?
No — the USDA PLANTS Database lists Calopo as introduced rather than native in the Lower 48, so it is not part of Arkansas's native flora. It grows here as a garden plant; pairing it with a few Arkansas natives keeps local pollinators fed too.
How should I amend the soil for Calopo in Arkansas?
Calopo tolerates pH 4.3-8 and well (dry spells) drainage (FAO ECOCROP). That is a 3.7-unit span, acid ground through alkaline, so pH is rarely what limits this plant on a Arkansas site — amend for drainage and organic matter first.
Will Calopo actually grow on my specific land in Arkansas?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores calopo 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 Arkansas
State-level data is a sketch. Your Growable Ground report scores calopo against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Arkansas calopo averages can't show:
We read public map data around Arkansas — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Arkansas calopo average
Explore More
Growing guides for calopo
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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