USDA Hardiness Zone 5b
Frost Dates for 52327 — Riverside, Iowa
NOAA 1991–2020 normals from Iowa City, IA (640 ft), 9 miles north.
Updated
In Riverside, the last spring frost (32°F) is around April 29 in half of years and has passed by May 14 in nine years out of ten. The first fall frost comes around October 9, as early as September 25 one year in ten, leaving a typical freeze-free season of 162 days (NOAA, Iowa City, IA).
- Last spring frost
- April 29
- First fall frost
- October 9
- Growing season
- 162 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 13
- Winters with snow
- 100%
- Snow per year
- 27.5"
median, 1991–2020
median, 1991–2020
29 of 29 observed
NOAA normal
Frost risk by date in Riverside
Half of springs at Iowa City, IA see their last 32°F night by April 29; only one in ten is past it by April 14, and one in ten still has one after May 14. Planting tender crops after May 5 leaves a 30% risk of a frost on them, after May 8 20%, and after May 14 10%. The 15 days between the even-odds date and the one-in-ten date is wider than at 82% of the 132 Iowa stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 9 in half of years, as early as September 25 one year in ten, and holds off past October 22 one year in ten. A hard freeze of 28°F follows 11 days later, around October 20; in spring the one-in-ten date for 28°F is May 5, 9 days before the 32°F one. The freeze-free season lasts 162 days in a typical year, shorter than at 61% of the 132 Iowa stations; it reaches 185 days one year in ten and falls short of 143 one year in ten. On average 130 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 8 days longer, to about May 7, and return around October 1. Severe cold of 16°F or below comes every winter, usually between November 18 and March 17.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 24 | Apr 29 | May 1 | May 5 | May 7 | May 10 | May 14 | May 16 | May 21 |
| 32°F | Apr 14 | Apr 18 | Apr 23 | Apr 26 | Apr 29 | May 1 | May 5 | May 8 | May 14 |
| 28°F | Apr 3 | Apr 8 | Apr 12 | Apr 16 | Apr 18 | Apr 22 | Apr 25 | Apr 30 | May 5 |
| 24°F | Mar 22 | Mar 29 | Apr 1 | Apr 4 | Apr 6 | Apr 9 | Apr 13 | Apr 19 | Apr 25 |
| 20°F | Mar 11 | Mar 17 | Mar 21 | Mar 26 | Mar 29 | Apr 1 | Apr 3 | Apr 6 | Apr 14 |
| 16°F | Mar 1 | Mar 7 | Mar 10 | Mar 13 | Mar 17 | Mar 21 | Mar 25 | Mar 29 | Apr 2 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 17 | Sep 22 | Sep 26 | Sep 28 | Oct 1 | Oct 3 | Oct 5 | Oct 8 | Oct 12 |
| 32°F | Sep 25 | Sep 30 | Oct 3 | Oct 6 | Oct 9 | Oct 12 | Oct 15 | Oct 18 | Oct 22 |
| 28°F | Oct 3 | Oct 10 | Oct 14 | Oct 18 | Oct 20 | Oct 22 | Oct 24 | Oct 27 | Nov 1 |
| 24°F | Oct 17 | Oct 21 | Oct 25 | Oct 28 | Oct 30 | Nov 1 | Nov 3 | Nov 7 | Nov 11 |
| 20°F | Oct 28 | Nov 1 | Nov 3 | Nov 6 | Nov 8 | Nov 11 | Nov 14 | Nov 17 | Nov 23 |
| 16°F | Nov 5 | Nov 8 | Nov 12 | Nov 15 | Nov 18 | Nov 21 | Nov 24 | Nov 28 | Dec 3 |
Freeze probabilities 1991–2020 at Iowa City, IA, 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 52327 →Compare Riverside with another place →
Weather by month in Riverside
July is the warmest month at Iowa City, IA, averaging 84°F by day and 63°F at night; January is the coldest at 29°F and 12°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 42% of years.
Warmth for growing adds up to 3,049 growing degree days a year (base 50°F), more than at 55% of the 132 Iowa stations. 35% of them (1,075) have built up by the end of June, and July adds the most, 727. Precipitation totals 38.6 inches a year, most in June (5.5") and least in January (1.1"); May to September bring 60% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 29 | 12 | 1.1 | 100% | 29 | 0 |
| Feb | 34 | 16 | 1.4 | 100% | 25 | 1 |
| Mar | 48 | 27 | 2.3 | 100% | 19 | 26 |
| Apr | 62 | 37 | 3.9 | 99% | 6 | 107 |
| May | 72 | 49 | 5.1 | 42% | <1 | 342 |
| Jun | 81 | 59 | 5.5 | 0% | 0 | 600 |
| Jul | 84 | 63 | 4.6 | 0% | 0 | 727 |
| Aug | 82 | 60 | 4.3 | 0% | 0 | 660 |
| Sep | 76 | 52 | 3.5 | 21% | <1 | 422 |
| Oct | 63 | 40 | 3.0 | 98% | 5 | 146 |
| Nov | 48 | 28 | 2.3 | 100% | 18 | 18 |
| Dec | 34 | 18 | 1.6 | 100% | 27 | 1 |
Monthly normals 1991–2020 at Iowa City, IA (640 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, Iowa City Municipal Airport, IA, 10 miles north of Riverside, has a last frost 8 days earlier (April 21), a first frost 9 days later (October 18), a season 18 days longer.
When it snows in Riverside, Iowa
The first measurable snow (0.1 inch or more) in Riverside usually arrives around December 1, and the last of the season around March 13. Those are the middle dates across the winters of 1991–2020 at Iowa City, IA, 9.3 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 47 days after the last snow.
Planting calendar for 52327
| When | What to do |
|---|---|
| February 18 – March 4 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 4 – March 18 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 1 – April 15 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 29 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 17 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 25 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 9 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 52327 is 9 miles from Iowa City, IA, which stands at 640 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 3 other ZIP codes share the station; its figures are presented in full for 52776 (West Liberty). The 2023 USDA Plant Hardiness Zone Map lists ZIP 52327 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.