USDA Hardiness Zone 7b
Frost Dates for 19901 — Dover, Delaware
NOAA 1991–2020 normals from Dover, DE (30 ft), 1 miles south.
Updated
In Dover, the last spring frost (32°F) is around April 4 in half of years and has passed by April 17 in nine years out of ten. The first fall frost comes around November 4, as early as October 23 one year in ten, leaving a typical freeze-free season of 214 days (NOAA, Dover, DE).
- Last spring frost
- April 4
- First fall frost
- November 4
- Growing season
- 214 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
- January 8
- Last snow
- February 23
- Winters with snow
- 92%
- Snow per year
- 13.2"
median, 1991–2020
median, 1991–2020
24 of 26 observed
NOAA normal
Frost risk by date in Dover
Half of springs at Dover, DE see their last 32°F night by April 4; only one in ten is past it by March 22, and one in ten still has one after April 17. Planting tender crops after April 9 leaves a 30% risk of a frost on them, after April 12 20%, and after April 17 10%. The 13 days between the even-odds date and the one-in-ten date is narrower than at 70% of the 10 Delaware stations behind this site's ZIP pages.
In fall the first 32°F night comes by November 4 in half of years, as early as October 23 one year in ten, and holds off past November 18 one year in ten. A hard freeze of 28°F follows 12 days later, around November 16; in spring the one-in-ten date for 28°F is April 5, 12 days before the 32°F one. The freeze-free season lasts 214 days in a typical year, longer than at 60% of the 10 Delaware stations; it reaches 234 days one year in ten and falls short of 195 one year in ten. On average 79 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 13 days longer, to about April 17, and return around October 25. Severe cold of 16°F or below comes in 97% of winters, usually between January 2 and February 17.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 3 | Apr 7 | Apr 11 | Apr 14 | Apr 17 | Apr 20 | Apr 23 | Apr 29 | May 5 |
| 32°F | Mar 22 | Mar 28 | Mar 31 | Apr 1 | Apr 4 | Apr 6 | Apr 9 | Apr 12 | Apr 17 |
| 28°F | Mar 8 | Mar 15 | Mar 19 | Mar 22 | Mar 25 | Mar 27 | Mar 30 | Apr 1 | Apr 5 |
| 24°F | Feb 26 | Mar 2 | Mar 6 | Mar 10 | Mar 13 | Mar 16 | Mar 19 | Mar 22 | Mar 27 |
| 20°F | Feb 8 | Feb 19 | Feb 25 | Feb 28 | Mar 3 | Mar 6 | Mar 9 | Mar 14 | Mar 19 |
| 16°F97% of yrs | Jan 24 | Feb 1 | Feb 6 | Feb 11 | Feb 17 | Feb 22 | Feb 27 | Mar 3 | Mar 9 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 12 | Oct 16 | Oct 20 | Oct 22 | Oct 25 | Oct 28 | Oct 31 | Nov 2 | Nov 6 |
| 32°F | Oct 23 | Oct 28 | Oct 31 | Nov 2 | Nov 4 | Nov 6 | Nov 9 | Nov 13 | Nov 18 |
| 28°F | Nov 3 | Nov 6 | Nov 9 | Nov 12 | Nov 16 | Nov 19 | Nov 22 | Nov 27 | Dec 3 |
| 24°F | Nov 11 | Nov 17 | Nov 21 | Nov 25 | Nov 30 | Dec 3 | Dec 7 | Dec 12 | Dec 20 |
| 20°F | Nov 25 | Dec 1 | Dec 5 | Dec 10 | Dec 16 | Dec 20 | Dec 25 | Jan 1 | Jan 7 |
| 16°F97% of yrs | Dec 10 | Dec 19 | Dec 25 | Dec 30 | Jan 2 | Jan 7 | Jan 12 | Jan 18 | Jan 28 |
Freeze probabilities 1991–2020 at Dover, 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 19901 →Compare Dover with another place →
Weather by month in Dover
July is the warmest month at Dover, DE, averaging 87°F by day and 69°F at night; January is the coldest at 44°F and 28°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 64% of years.
Warmth for growing adds up to 4,118 growing degree days a year (base 50°F), more than at 60% of the 10 Delaware stations. 35% of them (1,426) have built up by the end of June, and July adds the most, 866. Precipitation totals 47.7 inches a year, most in August (4.9") and least in February (3.1"); May to September bring 46% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 44 | 28 | 3.4 | 100% | 22 | 11 |
| Feb | 47 | 29 | 3.1 | 100% | 19 | 14 |
| Mar | 55 | 35 | 4.2 | 99% | 12 | 54 |
| Apr | 66 | 45 | 3.7 | 64% | 1 | 204 |
| May | 74 | 54 | 3.9 | 0% | 0 | 447 |
| Jun | 83 | 64 | 4.6 | 0% | 0 | 698 |
| Jul | 87 | 69 | 4.1 | 0% | 0 | 866 |
| Aug | 85 | 67 | 4.9 | 0% | 0 | 812 |
| Sep | 79 | 61 | 4.3 | 0% | 0 | 603 |
| Oct | 69 | 50 | 4.1 | 33% | <1 | 299 |
| Nov | 58 | 39 | 3.4 | 98% | 8 | 87 |
| Dec | 49 | 32 | 4.0 | 99% | 18 | 24 |
Monthly normals 1991–2020 at Dover, DE (30 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, Greenwood 2NE, DE, 24 miles south of Dover, has a last frost 7 days later (April 11), a first frost 5 days earlier (October 30), a season 14 days shorter.
When it snows in Dover, Delaware
The first measurable snow (0.1 inch or more) in Dover usually arrives around January 8, and the last of the season around February 23. Those are the middle dates across the winters of 1991–2020 at Dover, DE, 1.3 miles away: half of years saw snow earlier, half later. Snow fell in 92% of those winters. The last 32°F night of spring typically comes 40 days after the last snow.
Planting calendar for 19901
| When | What to do |
|---|---|
| January 24 – February 7 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| February 7 – February 21 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| March 7 – March 21 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| April 4 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by August 12 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by October 21 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| November 4 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 19901 is 1 mile from Dover, DE, which stands at 30 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 9 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 19901 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.