US Grow Zones

Dover, Delaware: planting zone & frost dates

Last updated · Sources: PRISM/OSU 2023 ZIP zone listings; NOAA NCEI 1991–2020 Climate Normals (station USC00072730); U.S. Census Bureau — see methodology

Dover is in USDA plant hardiness zone 7b, where the average coldest winter night reaches 5 to 10°F (-15.0 to -12.2°C). The typical last spring frost is around Apr 9 and the first fall frost around Oct 31.

Hardiness zone7B5 to 10°F
Last spring frostApr 930% chance of frost after
First fall frostOct 3130% chance of frost before
Growing season214 daysmedian frost-free days

Frost dates

ProbabilityLast spring frost (32°F)First fall frost (32°F)
Safer (10% risk)Apr 17Oct 23
Typical planning date (30% risk)Apr 9Oct 31
Median (50%)Apr 4Nov 4

How to read this: after the spring "10% risk" date, a 32°F frost happens in only about 1 year in 10. In fall, the "10% risk" date is the early end — a frost before it happens about 1 year in 10.

Frost data comes from NOAA station DOVER, DE (USC00072730), 1.3 mi (2.1 km) from the city center and 10 ft higher than the city center (+3 m). Record used for the 1991–2020 normals: 30 years.

Frost probability in spring and fall, Dover, DEChance of a 32°F frost in Dover, DE, NOAA 1991–2020. Spring: the chance of another frost falls from 90% on Mar 22 to 10% on Apr 17. Fall: the chance that the first frost has arrived rises from 10% on Oct 23 to 90% on Nov 18.0%50%100%Spring: later frostMar 1Mar 15Apr 1Apr 1530%: Apr 9Fall: frost arrivedNov 1Nov 15Dec 130%: Oct 3132°F frost28°F hard freezeplanning date
Shaded areas show the chance of a 32°F frost: falling through spring, rising through fall. The dashed line is the 28°F hard-freeze curve. Data: NOAA 1991–2020 Normals, station USC00072730.
Frost-free growing season in Dover, DE1 in 10 risk: Apr 17 to Oct 23 (189 days); 3 in 10 risk: Apr 9 to Oct 31 (205 days); Median (50%): Apr 4 to Nov 4 (214 days); No 28°F freeze: Mar 25 to Nov 16 (236 days). In 9 of 10 years the 32°F-free season is at least 195 days.Frost-free days, spring to fallJFMAMJJASOND1 in 10 risk189 days3 in 10 risk205 daysMedian (50%)214 daysNo 28°F freeze236 days
Frost-free window at three risk levels, plus the window between 28°F hard freezes. Read about what the probabilities mean.

Why your yard may differ from the station: microclimates.

Hardiness zone across Dover

All 3 ZIP codes covering Dover are in zone 7b.

ZIP codes in Dover and their zones
ZIPZoneShare of city land
199017b45.7%
199047b38.7%
199027b15.6%

Vegetable planting calendar for Dover

Dates are counted from the 30%-risk frost dates above (last frost Apr 9, first frost Oct 31). Shift a week later in cold spots or low-lying ground.

CropStart indoorsTransplant / plant outDirect sowFall crop sow/plant
TomatoFeb 12 – Feb 26Apr 16 – Apr 30——
PepperJan 29 – Feb 12Apr 23 – May 7——
LettuceFeb 26 – Mar 12Mar 26 – Apr 16Mar 12 – Apr 23Aug 22 – Sep 19
Green Beans——Apr 16 – May 21Aug 8 – Aug 22
Sweet Corn——Apr 16 – May 14—
Zucchini & Summer SquashMar 12 – Mar 19Apr 16 – Apr 30Apr 16 – May 7Aug 8 – Aug 22
CucumberMar 12 – Mar 19Apr 23 – Apr 30Apr 16 – May 7Aug 8 – Aug 22
Carrot——Mar 19 – Apr 23Aug 8 – Aug 22
OnionJan 15 – Jan 29Mar 12 – Mar 26——
Potato—Mar 12 – Apr 2——
BasilFeb 26 – Mar 12Apr 23 – May 7Apr 23 – May 14—
Spinach——Feb 26 – Mar 26Sep 5 – Oct 3
KaleFeb 12 – Feb 26Mar 12 – Apr 2Mar 12 – Apr 2Aug 22 – Sep 19
BroccoliFeb 12 – Feb 26Mar 26 – Apr 16—Aug 8 – Aug 22
Peas——Feb 26 – Mar 19Aug 22 – Sep 5
EggplantJan 29 – Feb 12Apr 23 – May 7——
CabbageFeb 12 – Feb 26Mar 12 – Mar 26—Aug 8 – Aug 22
Radish——Mar 5 – Apr 23Sep 19 – Oct 17
Strawberry—Mar 12 – Apr 2——
Beets——Mar 19 – Apr 30Aug 22 – Sep 5

Nearby cities in Delaware

More: all Delaware cities · other zone 7b cities: New York, NY, Philadelphia, PA, Oklahoma City, OK, Nashville, TN, Washington, DC, Baltimore, MD, Albuquerque, NM, Tulsa, OK

Dover gardening questions

When is the last frost in Dover, DE?

Plan around Apr 9. At NOAA's Dover, DE station, 1.3 mi from the city center, there is a 30% chance of a 32°F frost after that date. Half of springs have their last frost by Apr 4, and after Apr 17 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Mar 25. The last frost is fairly predictable here: only 26 days separate the 90% and 10% dates (median for cities on this site: 36 days).

When should I plant tomatoes in Dover, DE?

Start seeds indoors Feb 12 – Feb 26 and set transplants outside Apr 16 – Apr 30, once nights stay above 50°F and the soil is near 60°F. That leaves 205 days between the 30% frost dates, enough for most varieties including 80–85-day slicers. More: tomato planting dates by zone.

How long is the growing season in Dover?

About 214 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 195 days, and in 1 year in 10 it runs 234 days or more. In fall there is a 10% chance of frost by Oct 23 and a 30% chance by Oct 31.

When should I plant a fall garden in Dover?

Count back from the first fall frost (Oct 31): transplant broccoli Aug 8 – Aug 22; sow kale Aug 22 – Sep 19; sow lettuce Aug 22 – Sep 19; sow radishes Sep 19 – Oct 17. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Nov 16. How the math works: succession and fall planting.

Did Dover's hardiness zone change on the 2023 map?

Yes. Most of Dover was zone 7a on the 2012 map and is zone 7b on the 2023 map — half a zone warmer, like about 56% of U.S. ZIP codes. The shift comes from a newer 1991–2020 averaging period plus more weather stations and better mapping; it does not mean last frost comes earlier. Why the 2023 map is warmer.

How does Dover compare with Wilmington, DE?

Both are in zone 7b. The typical last spring frost in Dover (Apr 9) comes about 4 days earlier than in Wilmington, DE (Apr 13), 40 miles away, and the first fall frost is Oct 31 versus Oct 30. The two cities use different NOAA stations.