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

Planting zone for 37166 — Smithville, TN

ZIP code 37166 (Smithville, DeKalb County) is in USDA zone 7b: the coldest winter night averages 5 to 10 °F. The median last spring frost is April 18 and the first fall frost October 22.

Where ZIP 37166 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.

Zone7b5 to 10 °F

Coldest night−15 to −12.2 °C

Last frostApr 18

First frostOct 22

2012 zone7a

Was 7a 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 7b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Smithville, TN…

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 Smithville, TN

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostApril 18median — 50% chance of a later frost

Safe for tender plantsMay 2only 10% chance of frost after

First fall frostOctober 22median — 10% chance by Oct 10

Growing season187 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 4 and returns around November 1.

From the NOAA station Smithville 2 Se, TN — 2 miles away, elevation 889 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 37166

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 7 – Mar 21

SpinachSow outdoors · Mar 7 – Mar 28

Broccoli, cabbageStart indoors · Feb 7 – Feb 21

Broccoli, cabbageTransplant · Mar 28 – Apr 11

Onion setsPlant outdoors · Mar 21 – Apr 4

PotatoesPlant outdoors · Mar 28 – Apr 11

LettuceSow outdoors · Mar 21 – Apr 4

Carrots, beetsSow outdoors · Mar 28 – Apr 11

TomatoesStart indoors · Feb 21 – Mar 7

TomatoesTransplant · Apr 25 – May 9

Peppers, eggplantStart indoors · Feb 7 – Feb 21

Peppers, eggplantTransplant · May 2 – May 16

BeansSow outdoors · Apr 25 – May 9

Sweet cornSow outdoors · Apr 25 – May 9

Cucumbers, squashSow outdoors · Apr 25 – May 9

Fall lettuce, spinachSow outdoors · Aug 27 – Sep 10

GarlicPlant cloves · Oct 8 – Nov 12

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 18) and first fall frost (Oct 22) 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 37166 came on Feb 21 — 6 days earlier than the 1991–2020 average (Feb 27).

average
Feb 272026
Feb 21

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).

Soil in Smithville, TN

The soil mapped at the center of ZIP 37166 is Dickson — silt loam, moderately well drained.

TextureSilt loama good balance for most vegetables

pH6.2slightly acidic; most vegetables like 6.0–7.0

DrainageModerately well drainednatural drainage class

Organic matter2.8%moderate

Hydrologic groupC/Dslow when drained; wet otherwise

Farmland classprime farmlandUSDA classification

Map unit: Dickson silt loam, 2 to 5 percent slopes, eastern phase.

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 37166; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Smithville, TN

Summer high88 °Faverage high, July

Winter low26 °Faverage low, January

Hot days27days a year at 90 °F or more

Freezing nights102nights a year at 32 °F or less

Growing degree days4,066base 50 °F — the season’s usable heat

Longest day14 h 36 mindaylight on June 21

Shortest day9 h 43 mindaylight on December 21

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

Precipitation57 inper year, rain and melted snow

Snowfall3 inper year; 3 days with snow on the ground

Average high and low, by month

Precipitation by month inches · ❄ = snowfall

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Smithville 2 Se, TN (2 mi away); precipitation: Smithville 2 Se, TN (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 7b.

370597b

Dowelltown, TN · 8 mi

Silver Point, TN · 13 mi

385507b

Campaign, TN · 13 mi

385697b

Lancaster, TN · 14 mi

Tennessee planting zones →

Questions about 37166

What planting zone is ZIP code 37166?

ZIP code 37166 (Smithville, TN) is in USDA hardiness zone 7b on the 2023 map: the coldest night of an average winter reaches 5 to 10 °F (−15 to −12.2 °C).

When is the last frost in Smithville, TN?

The median last spring frost (32 °F) near 37166 is April 18; after May 2 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Smithville 2 Se station.

When is the first frost in Smithville, TN?

The median first fall frost near 37166 is October 22, giving a median frost-free growing season of 187 days.

When should I plant tomatoes in 37166?

Start tomato seeds indoors around Feb 21 – Mar 7 and set transplants outside around Apr 25 – May 9, one to three weeks after the median last frost.

How much rain and snow does 37166 get?

About 57 inches of precipitation a year and 3 inches of snowfall (NOAA 1991–2020 normals, Smithville 2 Se station).

How hot do summers get in Smithville, TN?

The average high peaks at 88 °F in July, with about 27 days a year at 90 °F or more.

What kind of soil does 37166 have?

The USDA soil survey maps Dickson at the center of ZIP 37166: silt loam, moderately well drained, pH about 6.2 (slightly acidic).

Did spring come early in Smithville, TN in 2026?

Spring leaf-out near 37166 came on Feb 21 in 2026, 6 days earlier than the 1991–2020 average (Feb 27), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Smithville, TN?

Intermediate onions: the longest day near 37166 is 14 h 36 min, so day-neutral types bulb best; long-day varieties may not bulb fully.

Did the zone for 37166 change?

Yes. The 2012 USDA map put 37166 in zone 7a; the 2023 map puts it in zone 7b. The newer map uses 1991–2020 data and more weather stations.