USDA Hardiness Zone 5b
Frost Dates for 61540 — Lacon, Illinois
NOAA 1991–2020 normals from Lacon, IL (458 ft), 2 miles southwest.
Updated
In Lacon, the last spring frost (32°F) is around April 20 in half of years and has passed by May 7 in nine years out of ten. The first fall frost comes around October 17, as early as October 3 one year in ten, leaving a typical freeze-free season of 178 days (NOAA, Lacon, IL).
- Last spring frost
- April 20
- First fall frost
- October 17
- Growing season
- 178 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
- November 29
- Last snow
- March 21
- Winters with snow
- 100%
- Snow per year
- 24.6"
median, 1991–2020
median, 1991–2020
26 of 26 observed
NOAA normal
Frost risk by date in Lacon
Half of springs at Lacon, IL see their last 32°F night by April 20; only one in ten is past it by April 5, and one in ten still has one after May 7. Planting tender crops after April 28 leaves a 30% risk of a frost on them, after May 1 20%, and after May 7 10%. The 17 days between the even-odds date and the one-in-ten date is wider than at 79% of the 158 Illinois stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 17 in half of years, as early as October 3 one year in ten, and holds off past November 1 one year in ten. A hard freeze of 28°F follows 11 days later, around October 28; in spring the one-in-ten date for 28°F is April 24, 13 days before the 32°F one. The freeze-free season lasts 178 days in a typical year, shorter than at 70% of the 158 Illinois stations; it reaches 200 days one year in ten and falls short of 156 one year in ten. On average 121 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 2, and return around October 7. Severe cold of 16°F or below comes every winter, usually between November 29 and March 8.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 17 | Apr 22 | Apr 26 | Apr 29 | May 2 | May 5 | May 9 | May 14 | May 20 |
| 32°F | Apr 5 | Apr 10 | Apr 13 | Apr 16 | Apr 20 | Apr 24 | Apr 28 | May 1 | May 7 |
| 28°F | Mar 22 | Mar 31 | Apr 2 | Apr 5 | Apr 7 | Apr 10 | Apr 14 | Apr 18 | Apr 24 |
| 24°F | Mar 9 | Mar 16 | Mar 21 | Mar 25 | Mar 29 | Apr 1 | Apr 3 | Apr 6 | Apr 11 |
| 20°F | Feb 28 | Mar 6 | Mar 10 | Mar 14 | Mar 18 | Mar 21 | Mar 25 | Mar 29 | Apr 2 |
| 16°F | Feb 18 | Feb 25 | Mar 1 | Mar 5 | Mar 8 | Mar 12 | Mar 15 | Mar 20 | Mar 25 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 23 | Sep 29 | Oct 2 | Oct 5 | Oct 7 | Oct 10 | Oct 13 | Oct 16 | Oct 20 |
| 32°F | Oct 3 | Oct 9 | Oct 12 | Oct 15 | Oct 17 | Oct 20 | Oct 23 | Oct 26 | Nov 1 |
| 28°F | Oct 15 | Oct 20 | Oct 24 | Oct 26 | Oct 28 | Oct 31 | Nov 3 | Nov 6 | Nov 12 |
| 24°F | Oct 26 | Oct 30 | Nov 1 | Nov 4 | Nov 7 | Nov 10 | Nov 15 | Nov 19 | Nov 26 |
| 20°F | Nov 4 | Nov 8 | Nov 12 | Nov 16 | Nov 20 | Nov 23 | Nov 27 | Dec 1 | Dec 5 |
| 16°F | Nov 12 | Nov 17 | Nov 22 | Nov 26 | Nov 29 | Dec 2 | Dec 5 | Dec 9 | Dec 16 |
Freeze probabilities 1991–2020 at Lacon, 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 61540 →Compare Lacon with another place →
Weather by month in Lacon
July is the warmest month at Lacon, IL, averaging 87°F by day and 65°F at night; January is the coldest at 34°F and 18°F. A freezing night is all but certain in every month from November to April (a 90% chance or more). From June to September the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 21% of years.
Warmth for growing adds up to 3,652 growing degree days a year (base 50°F), more than at 63% of the 158 Illinois stations. 36% of them (1,312) have built up by the end of June, and July adds the most, 808. Precipitation totals 38.6 inches a year, most in May (4.8") and least in January (2.1"); May to September bring 51% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 34 | 18 | 2.1 | 100% | 27 | 1 |
| Feb | 38 | 22 | 2.1 | 100% | 23 | 3 |
| Mar | 51 | 31 | 2.7 | 99% | 19 | 43 |
| Apr | 65 | 41 | 4.0 | 96% | 6 | 164 |
| May | 75 | 52 | 4.8 | 21% | <1 | 418 |
| Jun | 84 | 61 | 4.3 | 0% | 0 | 684 |
| Jul | 87 | 65 | 4.0 | 0% | 0 | 808 |
| Aug | 86 | 63 | 3.3 | 0% | 0 | 753 |
| Sep | 80 | 55 | 3.3 | 7% | <1 | 522 |
| Oct | 67 | 44 | 3.2 | 88% | 4 | 213 |
| Nov | 51 | 33 | 2.6 | 100% | 16 | 40 |
| Dec | 38 | 23 | 2.2 | 100% | 26 | 4 |
Monthly normals 1991–2020 at Lacon, IL (458 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, Hennepin Wtr Trmt Plt, IL, 16 miles north of Lacon, has a last frost 4 days later (April 24), the same first-frost date, a season 4 days shorter.
When it snows in Lacon, Illinois
The first measurable snow (0.1 inch or more) in Lacon usually arrives around November 29, and the last of the season around March 21. Those are the middle dates across the winters of 1991–2020 at Lacon, IL, 1.7 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 30 days after the last snow.
Planting calendar for 61540
| When | What to do |
|---|---|
| February 9 – February 23 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| February 23 – March 9 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 23 – April 6 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 20 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 25 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by October 3 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 17 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 61540 is 2 miles from Lacon, IL, which stands at 458 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station; its figures are presented in full for 61523 (Chillicothe). The 2023 USDA Plant Hardiness Zone Map lists ZIP 61540 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.