USDA Hardiness Zone 7b
Frost Dates for 19720 — New Castle, Delaware
NOAA 1991–2020 normals from Wilmington New Castle Co Airport, DE (79 ft), under a mile northwest.
Updated
In New Castle, the last spring frost (32°F) is around April 7 in half of years and has passed by April 21 in nine years out of ten. The first fall frost comes around November 1, as early as October 19 one year in ten, leaving a typical freeze-free season of 209 days (NOAA, Wilmington New Castle Co Airport, DE).
- Last spring frost
- April 7
- First fall frost
- November 1
- Growing season
- 209 days
- Hardiness zone
- 7b
50% probability
50% probability
freeze-free, 50%
5 to 10°F (-15.0 to -12.2°C) coldest night
- First snow
- December 16
- Last snow
- March 15
- Winters with snow
- 97%
- Snow per year
- 20.2"
median, 1991–2020
median, 1991–2020
29 of 30 observed
NOAA normal
Frost risk by date in New Castle
Half of springs at Wilmington New Castle Co Airport, DE see their last 32°F night by April 7; only one in ten is past it by March 26, and one in ten still has one after April 21. Planting tender crops after April 12 leaves a 30% risk of a frost on them, after April 16 20%, and after April 21 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 30% of the 10 Delaware stations behind this site's ZIP pages.
In fall the first 32°F night comes by November 1 in half of years, as early as October 19 one year in ten, and holds off past November 15 one year in ten. A hard freeze of 28°F follows 13 days later, around November 14; in spring the one-in-ten date for 28°F is April 9, 12 days before the 32°F one. The freeze-free season lasts 209 days in a typical year, shorter than at 50% of the 10 Delaware stations; it reaches 228 days one year in ten and falls short of 186 one year in ten. On average 92 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 14 days longer, to about April 21, and return around October 22. Severe cold of 16°F or below comes in 98% of winters, usually between January 1 and February 18.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 7 | Apr 12 | Apr 16 | Apr 18 | Apr 21 | Apr 23 | Apr 27 | May 1 | May 7 |
| 32°F | Mar 26 | Mar 31 | Apr 2 | Apr 4 | Apr 7 | Apr 10 | Apr 12 | Apr 16 | Apr 21 |
| 28°F | Mar 11 | Mar 17 | Mar 20 | Mar 24 | Mar 27 | Mar 31 | Apr 1 | Apr 4 | Apr 9 |
| 24°F | Feb 27 | Mar 4 | Mar 9 | Mar 12 | Mar 15 | Mar 18 | Mar 21 | Mar 24 | Mar 29 |
| 20°F | Feb 12 | Feb 19 | Feb 25 | Mar 1 | Mar 4 | Mar 7 | Mar 10 | Mar 14 | Mar 19 |
| 16°F98% of yrs | Jan 27 | Feb 4 | Feb 8 | Feb 13 | Feb 18 | Feb 23 | Feb 28 | Mar 4 | Mar 10 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 8 | Oct 13 | Oct 16 | Oct 19 | Oct 22 | Oct 24 | Oct 27 | Oct 31 | Nov 3 |
| 32°F | Oct 19 | Oct 24 | Oct 28 | Oct 31 | Nov 1 | Nov 4 | Nov 7 | Nov 11 | Nov 15 |
| 28°F | Nov 1 | Nov 4 | Nov 7 | Nov 11 | Nov 14 | Nov 16 | Nov 20 | Nov 25 | Dec 1 |
| 24°F | Nov 11 | Nov 15 | Nov 20 | Nov 24 | Nov 28 | Dec 1 | Dec 4 | Dec 8 | Dec 16 |
| 20°F | Nov 22 | Nov 30 | Dec 4 | Dec 8 | Dec 13 | Dec 18 | Dec 22 | Dec 28 | Jan 4 |
| 16°F98% of yrs | Dec 7 | Dec 14 | Dec 22 | Dec 28 | Jan 1 | Jan 4 | Jan 9 | Jan 15 | Jan 25 |
Freeze probabilities 1991–2020 at Wilmington New Castle Co Airport, DE, 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 19720 →Compare New Castle with another place →
Weather by month in New Castle
July is the warmest month at Wilmington New Castle Co Airport, DE, averaging 87°F by day and 68°F at night; January is the coldest at 41°F and 26°F. A freezing night is all but certain in every month from November to March (a 90% chance or more). From May to September the chance of a 32°F night stays under 10% each month. In spring, April still brings one in 75% of years.
Warmth for growing adds up to 3,841 growing degree days a year (base 50°F), fewer than at 60% of the 10 Delaware stations. 34% of them (1,309) have built up by the end of June, and July adds the most, 854. Precipitation totals 45.5 inches a year, most in June (4.7") and least in February (2.8"); May to September bring 46% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 41 | 26 | 3.2 | 100% | 24 | 5 |
| Feb | 44 | 27 | 2.8 | 100% | 21 | 6 |
| Mar | 53 | 34 | 4.2 | 100% | 14 | 38 |
| Apr | 64 | 44 | 3.5 | 75% | 2 | 165 |
| May | 74 | 53 | 3.6 | 2% | 0 | 418 |
| Jun | 82 | 63 | 4.7 | 0% | 0 | 678 |
| Jul | 87 | 68 | 4.4 | 0% | 0 | 854 |
| Aug | 85 | 67 | 4.0 | 0% | 0 | 798 |
| Sep | 79 | 59 | 4.4 | 0% | 0 | 567 |
| Oct | 67 | 47 | 3.7 | 42% | 1 | 243 |
| Nov | 56 | 37 | 3.1 | 99% | 10 | 58 |
| Dec | 46 | 30 | 3.9 | 100% | 20 | 12 |
Monthly normals 1991–2020 at Wilmington New Castle Co Airport, DE (79 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, Wilmington Porter Rsch, DE, 8 miles north of New Castle and 191 feet higher, has the same 50% last-frost date, a first frost 3 days later (November 4).
When it snows in New Castle, Delaware
The first measurable snow (0.1 inch or more) in New Castle usually arrives around December 16, and the last of the season around March 15. Those are the middle dates across the winters of 1991–2020 at Wilmington New Castle Co Airport, DE, 0.6 miles away: half of years saw snow earlier, half later. Snow fell in 97% of those winters. The last 32°F night of spring typically comes 23 days after the last snow.
Planting calendar for 19720
| When | What to do |
|---|---|
| January 27 – February 10 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| February 10 – February 24 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 10 – March 24 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 7 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by August 9 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by October 18 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| November 1 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 19720 is under a mile from Wilmington New Castle Co Airport, DE, which stands at 79 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 6 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 19720 in zone 7b, the band where the coldest night of the year averaged 5 to 10°F (-15.0 to -12.2°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.