USDA Hardiness Zone 5b
Frost Dates for 61356 — Princeton, Illinois
NOAA 1991–2020 normals from Princeton, IL (697 ft), under a mile southwest.
Updated
In Princeton, the last spring frost (32°F) is around April 22 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 177 days (NOAA, Princeton, IL).
- Last spring frost
- April 22
- First fall frost
- October 17
- Growing season
- 177 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 26
- Last snow
- March 22
- Winters with snow
- 100%
- Snow per year
- 28.5"
median, 1991–2020
median, 1991–2020
30 of 30 observed
NOAA normal
Frost risk by date in Princeton
Half of springs at Princeton, 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 7. Planting tender crops after April 29 leaves a 30% risk of a frost on them, after May 1 20%, and after May 7 10%. The 15 days between the even-odds date and the one-in-ten date is narrower than at 54% 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 October 29 one year in ten. A hard freeze of 28°F follows 10 days later, around October 27; in spring the one-in-ten date for 28°F is April 26, 11 days before the 32°F one. The freeze-free season lasts 177 days in a typical year, shorter than at 72% of the 158 Illinois stations; it reaches 194 days one year in ten and falls short of 156 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 11 days longer, to about May 3, and return around October 6. Severe cold of 16°F or below comes every winter, usually between November 25 and March 14.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 19 | Apr 24 | Apr 28 | Apr 30 | May 3 | May 6 | May 9 | May 12 | May 17 |
| 32°F | Apr 9 | Apr 14 | Apr 17 | Apr 20 | Apr 22 | Apr 26 | Apr 29 | May 1 | May 7 |
| 28°F | Mar 31 | Apr 4 | Apr 6 | Apr 9 | Apr 12 | Apr 14 | Apr 17 | Apr 20 | Apr 26 |
| 24°F | Mar 16 | Mar 22 | Mar 27 | Mar 31 | Apr 2 | Apr 4 | Apr 6 | Apr 9 | Apr 14 |
| 20°F | Mar 8 | Mar 12 | Mar 16 | Mar 20 | Mar 23 | Mar 26 | Mar 30 | Apr 2 | Apr 5 |
| 16°F | Feb 27 | Mar 4 | Mar 8 | Mar 11 | Mar 14 | Mar 17 | Mar 20 | Mar 24 | Mar 30 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 23 | Sep 27 | Oct 1 | Oct 3 | Oct 6 | Oct 9 | Oct 12 | Oct 15 | Oct 20 |
| 32°F | Oct 3 | Oct 8 | Oct 12 | Oct 15 | Oct 17 | Oct 20 | Oct 22 | Oct 25 | Oct 29 |
| 28°F | Oct 14 | Oct 19 | Oct 22 | Oct 24 | Oct 27 | Oct 30 | Nov 1 | Nov 3 | Nov 9 |
| 24°F | Oct 25 | Oct 30 | Nov 1 | Nov 3 | Nov 6 | Nov 8 | Nov 11 | Nov 15 | Nov 20 |
| 20°F | Nov 3 | Nov 7 | Nov 10 | Nov 13 | Nov 16 | Nov 19 | Nov 23 | Nov 26 | Nov 30 |
| 16°F | Nov 9 | Nov 15 | Nov 18 | Nov 22 | Nov 25 | Nov 28 | Dec 1 | Dec 5 | Dec 12 |
Freeze probabilities 1991–2020 at Princeton, 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 61356 →Compare Princeton with another place →
Weather by month in Princeton
July is the warmest month at Princeton, IL, averaging 85°F by day and 63°F at night; January is the coldest at 30°F and 14°F. A freezing night is all but certain in every month from October 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 3,152 growing degree days a year (base 50°F), fewer than at 74% of the 158 Illinois stations. 36% of them (1,120) have built up by the end of June, and July adds the most, 739. Precipitation totals 39.7 inches a year, most in May (5.1") and least in January (2.0"); May to September bring 54% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 30 | 14 | 2.0 | 100% | 29 | 0 |
| Feb | 35 | 18 | 2.0 | 100% | 25 | 1 |
| Mar | 48 | 28 | 2.5 | 100% | 21 | 29 |
| Apr | 62 | 38 | 4.0 | 98% | 6 | 114 |
| May | 73 | 50 | 5.1 | 21% | <1 | 358 |
| Jun | 82 | 60 | 4.6 | 0% | 0 | 618 |
| Jul | 85 | 63 | 3.7 | 0% | 0 | 739 |
| Aug | 82 | 61 | 4.0 | 0% | 0 | 673 |
| Sep | 76 | 53 | 3.9 | 7% | 0 | 440 |
| Oct | 63 | 42 | 3.1 | 94% | 3 | 156 |
| Nov | 48 | 30 | 2.6 | 100% | 17 | 23 |
| Dec | 35 | 20 | 2.2 | 100% | 27 | 2 |
Monthly normals 1991–2020 at Princeton, IL (697 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, 9 miles southeast of Princeton and 237 feet lower, has a last frost 2 days later (April 24), the same first-frost date, a season 3 days shorter.
When it snows in Princeton, Illinois
The first measurable snow (0.1 inch or more) in Princeton usually arrives around November 26, and the last of the season around March 22. Those are the middle dates across the winters of 1991–2020 at Princeton, IL, 0.6 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 31 days after the last snow.
Planting calendar for 61356
| 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 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 61356 is under a mile from Princeton, IL, which stands at 697 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 61356 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.