USDA Hardiness Zone 5b
Frost Dates for 61462 — Monmouth, Illinois
NOAA 1991–2020 normals from Monmouth, IL (720 ft), 2 miles north.
Updated
In Monmouth, the last spring frost (32°F) is around April 22 in half of years and has passed by May 10 in nine years out of ten. The first fall frost comes around October 15, as early as September 29 one year in ten, leaving a typical freeze-free season of 174 days (NOAA, Monmouth, IL).
- Last spring frost
- April 22
- First fall frost
- October 15
- Growing season
- 174 days
- Hardiness zone
- 5b
50% probability
50% probability
freeze-free, 50%
-15 to -10°F (-26.1 to -23.3°C) coldest night
- First snow
- December 1
- Last snow
- March 17
- Winters with snow
- 100%
- Snow per year
- 25.6"
median, 1991–2020
median, 1991–2020
28 of 28 observed
NOAA normal
Frost risk by date in Monmouth
Half of springs at Monmouth, IL see their last 32°F night by April 22; only one in ten is past it by April 9, and one in ten still has one after May 10. Planting tender crops after April 30 leaves a 30% risk of a frost on them, after May 3 20%, and after May 10 10%. The 18 days between the even-odds date and the one-in-ten date is wider than at 92% of the 158 Illinois stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 15 in half of years, as early as September 29 one year in ten, and holds off past October 27 one year in ten. A hard freeze of 28°F follows 10 days later, around October 25; in spring the one-in-ten date for 28°F is April 28, 12 days before the 32°F one. The freeze-free season lasts 174 days in a typical year, shorter than at 76% of the 158 Illinois stations; it reaches 192 days one year in ten and falls short of 153 one year in ten. On average 127 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 12 days longer, to about May 4, and return around October 5. Severe cold of 16°F or below comes every winter, usually between November 24 and March 12.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 20 | Apr 25 | Apr 28 | May 1 | May 4 | May 6 | May 10 | May 14 | May 20 |
| 32°F | Apr 9 | Apr 13 | Apr 17 | Apr 19 | Apr 22 | Apr 26 | Apr 30 | May 3 | May 10 |
| 28°F | Mar 30 | Apr 3 | Apr 6 | Apr 9 | Apr 11 | Apr 15 | Apr 18 | Apr 22 | Apr 28 |
| 24°F | Mar 15 | Mar 22 | Mar 27 | Mar 31 | Apr 2 | Apr 4 | Apr 6 | Apr 11 | Apr 17 |
| 20°F | Mar 6 | Mar 11 | Mar 14 | Mar 18 | Mar 21 | Mar 25 | Mar 29 | Apr 1 | Apr 6 |
| 16°F | Feb 26 | Mar 3 | Mar 6 | Mar 9 | Mar 12 | Mar 15 | Mar 18 | Mar 23 | Mar 29 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 20 | Sep 25 | Sep 29 | Oct 2 | Oct 5 | Oct 7 | Oct 10 | Oct 14 | Oct 18 |
| 32°F | Sep 29 | Oct 5 | Oct 9 | Oct 12 | Oct 15 | Oct 18 | Oct 20 | Oct 24 | Oct 27 |
| 28°F | Oct 11 | Oct 17 | Oct 20 | Oct 23 | Oct 25 | Oct 28 | Oct 30 | Nov 2 | Nov 7 |
| 24°F | Oct 23 | Oct 27 | Oct 30 | Nov 1 | Nov 3 | Nov 6 | Nov 9 | Nov 14 | Nov 20 |
| 20°F | Nov 1 | Nov 4 | Nov 8 | Nov 10 | Nov 14 | Nov 17 | Nov 21 | Nov 25 | Dec 1 |
| 16°F | Nov 8 | Nov 13 | Nov 17 | Nov 21 | Nov 24 | Nov 27 | Dec 1 | Dec 5 | Dec 11 |
Freeze probabilities 1991–2020 at Monmouth, IL, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 61462 →Compare Monmouth with another place →
Weather by month in Monmouth
July is the warmest month at Monmouth, IL, averaging 84°F by day and 64°F at night; January is the coldest at 31°F and 15°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 28% of years.
Warmth for growing adds up to 3,283 growing degree days a year (base 50°F), fewer than at 65% of the 158 Illinois stations. 36% of them (1,175) have built up by the end of June, and July adds the most, 739. Precipitation totals 39.6 inches a year, most in May (5.2") and least in January (1.9"); May to September bring 54% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 31 | 15 | 1.9 | 100% | 29 | 0 |
| Feb | 36 | 19 | 2.0 | 100% | 25 | 3 |
| Mar | 50 | 29 | 2.6 | 100% | 19 | 36 |
| Apr | 63 | 40 | 4.0 | 98% | 7 | 137 |
| May | 73 | 51 | 5.2 | 28% | <1 | 378 |
| Jun | 81 | 60 | 4.5 | 0% | 0 | 622 |
| Jul | 84 | 64 | 4.0 | 0% | 0 | 739 |
| Aug | 83 | 62 | 3.9 | 0% | 0 | 687 |
| Sep | 77 | 54 | 3.7 | 12% | <1 | 466 |
| Oct | 65 | 42 | 3.0 | 95% | 4 | 183 |
| Nov | 49 | 31 | 2.6 | 100% | 17 | 31 |
| Dec | 37 | 21 | 2.2 | 100% | 26 | 2 |
Monthly normals 1991–2020 at Monmouth, IL (720 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, Galesburg, IL, 14 miles east of Monmouth, has a last frost 2 days earlier (April 20), a first frost 4 days later (October 19), a season 6 days longer.
When it snows in Monmouth, Illinois
The first measurable snow (0.1 inch or more) in Monmouth usually arrives around December 1, and the last of the season around March 17. Those are the middle dates across the winters of 1991–2020 at Monmouth, IL, 1.8 miles away: half of years saw snow earlier, half later. Every one of those winters saw snow. The last 32°F night of spring typically comes 36 days after the last snow.
Planting calendar for 61462
| When | What to do |
|---|---|
| February 11 – February 25 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| February 25 – March 11 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 25 – April 8 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 22 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 23 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by October 1 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 15 onward | Plant garlic, mulch beds, lift tender bulbsGarlic wants a cold spell; bare soil loses structure over winter. |
The weeks before and after the 50% dates are general rules of thumb, not NOAA figures; a seed packet gives the timing for each variety.
Where these figures come from
ZIP 61462 is 2 miles from Monmouth, IL, which stands at 720 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 61462 in zone 5b, the band where the coldest night of the year averaged -15 to -10°F (-26.1 to -23.3°C) over 1991–2020; a zone describes winter lows, not frost dates.
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.