US Grow Zones

Wilmington, Delaware: planting zone & frost dates

Last updated · Sources: PRISM/OSU 2023 ZIP zone listings; NOAA NCEI 1991–2020 Climate Normals (station USC00079605); U.S. Census Bureau — see methodology

Wilmington 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 13 and the first fall frost around Oct 30.

Hardiness zone7B5 to 10°F
Last spring frostApr 1330% chance of frost after
First fall frostOct 3030% chance of frost before
Growing season209 daysmedian frost-free days

Frost dates

ProbabilityLast spring frost (32°F)First fall frost (32°F)
Safer (10% risk)Apr 24Oct 21
Typical planning date (30% risk)Apr 13Oct 30
Median (50%)Apr 7Nov 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 WILMINGTON PORTER RSCH, DE (USC00079605), 2.7 mi (4.3 km) from the city center and 266 ft higher than the city center (+81 m). Record used for the 1991–2020 normals: 29 years.

Frost probability in spring and fall, Wilmington, DEChance of a 32°F frost in Wilmington, DE, NOAA 1991–2020. Spring: the chance of another frost falls from 90% on Mar 26 to 10% on Apr 24. Fall: the chance that the first frost has arrived rises from 10% on Oct 21 to 90% on Nov 19.0%50%100%Spring: later frostMar 15Apr 1Apr 15May 130%: Apr 13Fall: frost arrivedOct 15Nov 1Nov 15Dec 130%: Oct 3032°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 USC00079605.
Frost-free growing season in Wilmington, DE1 in 10 risk: Apr 24 to Oct 21 (180 days); 3 in 10 risk: Apr 13 to Oct 30 (200 days); Median (50%): Apr 7 to Nov 4 (211 days); No 28°F freeze: Mar 29 to Nov 15 (231 days). In 9 of 10 years the 32°F-free season is at least 189 days.Frost-free days, spring to fallJFMAMJJASOND1 in 10 risk180 days3 in 10 risk200 daysMedian (50%)211 daysNo 28°F freeze231 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 Wilmington

All 5 ZIP codes covering Wilmington are in zone 7b.

ZIP codes in Wilmington and their zones
ZIPZoneShare of city land
198017b31.6%
198027b21.9%
198097b18.6%
198057b15.2%
198067b12.5%

Vegetable planting calendar for Wilmington

Dates are counted from the 30%-risk frost dates above (last frost Apr 13, first frost Oct 30). Shift a week later in cold spots or low-lying ground.

CropStart indoorsTransplant / plant outDirect sowFall crop sow/plant
TomatoFeb 16 – Mar 2Apr 20 – May 4——
PepperFeb 2 – Feb 16Apr 27 – May 11——
LettuceMar 2 – Mar 16Mar 30 – Apr 20Mar 16 – Apr 27Aug 21 – Sep 18
Green Beans——Apr 20 – May 25Aug 7 – Aug 21
Sweet Corn——Apr 20 – May 18—
Zucchini & Summer SquashMar 16 – Mar 23Apr 20 – May 4Apr 20 – May 11Aug 7 – Aug 21
CucumberMar 16 – Mar 23Apr 27 – May 4Apr 20 – May 11Aug 7 – Aug 21
Carrot——Mar 23 – Apr 27Aug 7 – Aug 21
OnionJan 19 – Feb 2Mar 16 – Mar 30——
Potato—Mar 16 – Apr 6——
BasilMar 2 – Mar 16Apr 27 – May 11Apr 27 – May 18—
Spinach——Mar 2 – Mar 30Sep 4 – Oct 2
KaleFeb 16 – Mar 2Mar 16 – Apr 6Mar 16 – Apr 6Aug 21 – Sep 18
BroccoliFeb 16 – Mar 2Mar 30 – Apr 20—Aug 7 – Aug 21
Peas——Mar 2 – Mar 23Aug 21 – Sep 4
EggplantFeb 2 – Feb 16Apr 27 – May 11——
CabbageFeb 16 – Mar 2Mar 16 – Mar 30—Aug 7 – Aug 21
Radish——Mar 9 – Apr 27Sep 18 – Oct 16
Strawberry—Mar 16 – Apr 6——
Beets——Mar 23 – May 4Aug 21 – Sep 4

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

Wilmington gardening questions

When is the last frost in Wilmington, DE?

Plan around Apr 13. At NOAA's Wilmington Porter Rsch, DE station, 2.7 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 7, and after Apr 24 the risk drops to about 1 in 10. A hard freeze (28°F) usually ends earlier, around Mar 29. The 90% and 10% dates are 29 days apart, close to the 36-day median for cities on this site.

When should I plant tomatoes in Wilmington, DE?

Start seeds indoors Feb 16 – Mar 2 and set transplants outside Apr 20 – May 4, once nights stay above 50°F and the soil is near 60°F. That leaves 200 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 Wilmington?

About 209 days without a 32°F frost in a typical (median) year. In 9 years out of 10 the season lasts at least 189 days, and in 1 year in 10 it runs 229 days or more. In fall there is a 10% chance of frost by Oct 21 and a 30% chance by Oct 30.

When should I plant a fall garden in Wilmington?

Count back from the first fall frost (Oct 30): transplant broccoli Aug 7 – Aug 21; sow kale Aug 21 – Sep 18; sow lettuce Aug 21 – Sep 18; sow radishes Sep 18 – Oct 16. Hardy crops keep growing through light frosts; the median 28°F hard freeze here is Nov 15. How the math works: succession and fall planting.

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

Yes. Most of Wilmington 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 Wilmington compare with Philadelphia, PA?

Both are in zone 7b. The typical last spring frost in Wilmington (Apr 13) comes about 9 days later than in Philadelphia, PA (Apr 4), 28 miles away, and the first fall frost is Oct 30 versus Nov 11. The two cities use different NOAA stations.