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

Planting zone for 61350 — Ottawa, IL

ZIP code 61350 (Ottawa, LaSalle County) is in USDA zone 5b: the coldest winter night averages −15 to −10 °F. The median last spring frost is April 20 and the first fall frost October 22.

Where ZIP 61350 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.

Zone5b−15 to −10 °F

Coldest night−26.1 to −23.3 °C

Last frostApr 20

First frostOct 22

2012 zone5b

Same zone as on the 2012 map. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 5b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Ottawa, IL…

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 Ottawa, IL

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostApril 20median — 50% chance of a later frost

Safe for tender plantsMay 5only 10% chance of frost after

First fall frostOctober 22median — 10% chance by Oct 7

Growing season183 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 8 and returns around November 1.

From the NOAA station Ottawa 5sw, IL — 4 miles away, elevation 525 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 61350

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 9 – Mar 23

SpinachSow outdoors · Mar 9 – Mar 30

Broccoli, cabbageStart indoors · Feb 9 – Feb 23

Broccoli, cabbageTransplant · Mar 30 – Apr 13

Onion setsPlant outdoors · Mar 23 – Apr 6

PotatoesPlant outdoors · Mar 30 – Apr 13

LettuceSow outdoors · Mar 23 – Apr 6

Carrots, beetsSow outdoors · Mar 30 – Apr 13

TomatoesStart indoors · Feb 23 – Mar 9

TomatoesTransplant · Apr 27 – May 11

Peppers, eggplantStart indoors · Feb 9 – Feb 23

Peppers, eggplantTransplant · May 4 – May 18

BeansSow outdoors · Apr 27 – May 11

Sweet cornSow outdoors · Apr 27 – May 11

Cucumbers, squashSow outdoors · Apr 27 – May 11

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 20) 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 61350 came on Mar 19 — 16 days earlier than the 1991–2020 average (Apr 4).

average
Apr 42026
Mar 19

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 Ottawa, IL

The soil mapped at the center of ZIP 61350 is Flanagan — silt loam, somewhat poorly drained.

TextureSilt loama good balance for most vegetables

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

DrainageSomewhat poorly drainedconsider raised beds

Organic matter4%moderate

Hydrologic groupC/Dslow when drained; wet otherwise

Farmland classprime farmlandUSDA classification

Map unit: Flanagan silt loam, 0 to 2 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 61350; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Ottawa, IL

Summer high83 °Faverage high, July

Winter low15 °Faverage low, January

Hot days17days a year at 90 °F or more

Freezing nights129nights a year at 32 °F or less

Growing degree days3,202base 50 °F — the season’s usable heat

Longest day15 h 10 mindaylight on June 21

Shortest day9 h 11 mindaylight on December 21

Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)

Precipitation40.1 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: Ottawa 5sw, IL (4 mi away); precipitation: Ottawa 1.3 Nw, IL (within 1 mile). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5b.

Marseilles, IL · 9 mi

613255b

Grand Ridge, IL · 10 mi

Troy Grove, IL · 13 mi

Illinois planting zones →

Questions about 61350

What planting zone is ZIP code 61350?

ZIP code 61350 (Ottawa, IL) is in USDA hardiness zone 5b on the 2023 map: the coldest night of an average winter reaches −15 to −10 °F (−26.1 to −23.3 °C).

When is the last frost in Ottawa, IL?

The median last spring frost (32 °F) near 61350 is April 20; after May 5 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Ottawa 5sw station.

When is the first frost in Ottawa, IL?

The median first fall frost near 61350 is October 22, giving a median frost-free growing season of 183 days.

When should I plant tomatoes in 61350?

Start tomato seeds indoors around Feb 23 – Mar 9 and set transplants outside around Apr 27 – May 11, one to three weeks after the median last frost.

How much rain and snow does 61350 get?

About 40.1 inches of precipitation a year (NOAA 1991–2020 normals, Ottawa 1.3 Nw station).

How hot do summers get in Ottawa, IL?

The average high peaks at 83 °F in July, with about 17 days a year at 90 °F or more.

What kind of soil does 61350 have?

The USDA soil survey maps Flanagan at the center of ZIP 61350: silt loam, somewhat poorly drained, pH about 6.2 (slightly acidic).

Did spring come early in Ottawa, IL in 2026?

Spring leaf-out near 61350 came on Mar 19 in 2026, 16 days earlier than the 1991–2020 average (Apr 4), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Ottawa, IL?

Long-day onions: the longest day near 61350 is 15 h 10 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).