Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 29, 2026

Planting zone for 72845 — Knoxville, AR

ZIP code 72845 (Knoxville, Johnson County) is in USDA zone 8a: the coldest winter night averages 10 to 15 °F. The median last spring frost is March 24 and the first fall frost November 10.

Where ZIP 72845 is

Outlined: the ZIP code area · tap the map for the zone at any spot · scroll or pinch to zoom

Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.

Zone8a10 to 15 °F

Coldest night−12.2 to −9.4 °C

Last frostMar 24

First frostNov 10

2012 zone7b

Was 7b on the 2012 map — half a zone warmer now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 8a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Knoxville, AR…

Forecast data: National Weather Service (api.weather.gov), public domain. This is not a warning service — for official frost and freeze warnings see weather.gov.

Frost dates in Knoxville, AR

JanFebMarAprMayJunJulAugSepOctNovDec

Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free

Last spring frostMarch 24median — 50% chance of a later frost

Safe for tender plantsApril 10only 10% chance of frost after

First fall frostNovember 10median — 10% chance by Oct 28

Growing season233 daysfrost-free, median

A hard freeze (28 °F) usually ends around March 9 and returns around November 24.

From the NOAA station Clarksville 2n, AR — 11 miles away, elevation 449 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in 72845

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Feb 10 – Feb 24

SpinachSow outdoors · Feb 10 – Mar 3

Broccoli, cabbageStart indoors · Jan 13 – Jan 27

Broccoli, cabbageTransplant · Mar 3 – Mar 17

Onion setsPlant outdoors · Feb 24 – Mar 10

PotatoesPlant outdoors · Mar 3 – Mar 17

LettuceSow outdoors · Feb 24 – Mar 10

Carrots, beetsSow outdoors · Mar 3 – Mar 17

TomatoesStart indoors · Jan 27 – Feb 10

TomatoesTransplant · Mar 31 – Apr 14

Peppers, eggplantStart indoors · Jan 13 – Jan 27

Peppers, eggplantTransplant · Apr 7 – Apr 21

BeansSow outdoors · Mar 31 – Apr 14

Sweet cornSow outdoors · Mar 31 – Apr 14

Cucumbers, squashSow outdoors · Mar 31 – Apr 14

Fall lettuce, spinachSow outdoors · Sep 15 – Sep 29

GarlicPlant cloves · Oct 27 – Dec 1

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Mar 24) and first fall frost (Nov 10) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 72845 came on Feb 13 — 8 days earlier than the 1991–2020 average (Feb 21).

average
Feb 212026
Feb 13

JanFebMarAprMayJun

The Spring Index marks the day when accumulated warmth is enough for lilac and honeysuckle to leaf out — a widely used signal that the growing season has started. Source: USA National Phenology Network, www.usanpn.org — Spring Indices, first leaf, 2026 (data as of 2026-09-08) and 30-year average 1991–2020 (CC BY 4.0).

Native plants for zone 8a in Arkansas

516 plants native to the lower 48 states, recorded in Arkansas, and rated by the USDA to survive 10 °F or colder — the bottom of zone 8a. Each links to its USDA PLANTS profile.

Source: USDA, NRCS. 2026. The PLANTS Database (plants.usda.gov), National Plant Data Team — state distribution, native status and the “Temperature, Minimum” characteristic. Check light, moisture and soil needs before buying; local nurseries and your state native plant society can confirm what thrives in Knoxville, AR.

Soil in Knoxville, AR

The soil mapped at the center of ZIP 72845 is Cane — fine sandy loam, moderately well drained.

TextureFine sandy loamdrains and warms fast; dries out and needs more feeding

pH5.3strongly acidic; most vegetables like 6.0–7.0

DrainageModerately well drainednatural drainage class

Organic matter1.25%low — add compost

Hydrologic groupCwater soaks in slowly

Farmland classFarmland of statewide importanceUSDA classification

Map unit: Cane fine sandy loam, 3 to 8 percent slopes.

Soil Survey Staff, Natural Resources Conservation Service, USDA. Soil Survey Geographic (SSURGO) Database, via Soil Data Access, accessed 2026-10-29. The soil at the center point of ZIP 72845; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Knoxville, AR

Summer high92 °Faverage high, July

Winter low29 °Faverage low, January

Hot days61days a year at 90 °F or more

Freezing nights70nights a year at 32 °F or less

Growing degree days5,085base 50 °F — the season’s usable heat

Longest day14 h 33 mindaylight on June 21

Shortest day9 h 46 mindaylight on December 21

Onions to growIntermediateday-neutral types bulb best; long-day varieties may not bulb fully

Precipitation49.8 inper year, rain and melted snow

Average high and low, by month

Precipitation by month inches

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Clarksville 2n, AR (11 mi away); precipitation: Scranton 5.4 Ene, AR (4 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 8a.

New Blaine, AR · 8 mi

Clarksville, AR · 13 mi

728018a

Russellville, AR · 14 mi

Arkansas planting zones →

Questions about 72845

What planting zone is ZIP code 72845?

ZIP code 72845 (Knoxville, AR) is in USDA hardiness zone 8a on the 2023 map: the coldest night of an average winter reaches 10 to 15 °F (−12.2 to −9.4 °C).

When is the last frost in Knoxville, AR?

The median last spring frost (32 °F) near 72845 is March 24; after April 10 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Clarksville 2n station.

When is the first frost in Knoxville, AR?

The median first fall frost near 72845 is November 10, giving a median frost-free growing season of 233 days.

When should I plant tomatoes in 72845?

Start tomato seeds indoors around Jan 27 – Feb 10 and set transplants outside around Mar 31 – Apr 14, one to three weeks after the median last frost.

How much rain and snow does 72845 get?

About 49.8 inches of precipitation a year (NOAA 1991–2020 normals, Scranton 5.4 Ene station).

How hot do summers get in Knoxville, AR?

The average high peaks at 92 °F in July, with about 61 days a year at 90 °F or more.

What kind of soil does 72845 have?

The USDA soil survey maps Cane at the center of ZIP 72845: fine sandy loam, moderately well drained, pH about 5.3 (strongly acidic).

Did spring come early in Knoxville, AR in 2026?

Spring leaf-out near 72845 came on Feb 13 in 2026, 8 days earlier than the 1991–2020 average (Feb 21), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Knoxville, AR?

Intermediate onions: the longest day near 72845 is 14 h 33 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 72845 change?

Yes. The 2012 USDA map put 72845 in zone 7b; the 2023 map puts it in zone 8a. The newer map uses 1991–2020 data and more weather stations.