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Frost dates and planting calendar for Wilmington, Delaware

Updated October 30, 2026. Based on USDA, NOAA and Colorado State University Extension data. Published by Humblebee.

USDA hardiness zone
7b[1]
Median last spring frost
Apr 7[2]
Median first fall frost
Nov 4[3]
Growing season, median
209 days[4]

Wilmington, Delaware is in USDA hardiness zone 7b on the 2023 map[1]. The median last spring frost is April 7, so in half of years the last frost comes after that date[2].

Frost dates

JanFebMarAprMayJunJulAugSepOctNovDecLast spring frost: 9 in 10 years after Mar 26, half of years Apr 7, 1 in 10 years after Apr 24Last frostmedian Apr 7First fall frost: 9 in 10 years before Nov 19, half of years Nov 4, 1 in 10 years before Oct 21First frostmedian Nov 4Frost riskHardyHardy vegetables: plant Mar 10 to Mar 24Mar 10 to Mar 24Semi-hardySemi-hardy vegetables: plant Mar 24 to Apr 7Mar 24 to Apr 7TenderTender vegetables: plant around Apr 7around Apr 7Very tenderVery tender vegetables: plant from Apr 21from Apr 21
Shaded: the span between the dates frost passes in 9 of 10 years and 1 of 10 years[2][3]. Green: planting windows from the CSU rules applied to the median last frost (GardenFacts calculation)[6]. Exact dates are in the tables below.

These frost dates are odds from NOAA records for 1991 to 2020, not a forecast[5]. They come from the Wilmington Porter Rsch weather station[5]. The last spring frost comes after March 26 in 9 of 10 years, and after April 24 in 1 of 10 years[2]. The first fall frost comes before October 21 in 1 of 10 years, and before November 4 in half of years[3]. Any single year can be earlier or later than these dates[2][3].

Frost Likely (9 in 10 years) Even odds (5 in 10) Unlikely (1 in 10)
Last spring frost (32°F)[2] after March 26 after April 7 after April 24
First fall frost (32°F)[3] before October 21 before November 4 before November 19
  • Hard freeze (28°F): median last spring date March 29, median first fall date November 15[7].
  • Frost-free growing season: at least 189 days in 9 of 10 years, 209 days in half of years and 229 days in 1 of 10 years[4].
  • The low reached 32°F or colder in 100% of years and 28°F or colder in 100% of years[8].
  • Weather station: Wilmington Porter Rsch (USC00079605), 2.7 miles from the city center, 270 feet, 29 years of 1991 to 2020 records[5].

When to plant vegetables

Colorado State University Extension's planting guide was written for Colorado[6]. GardenFacts used the NOAA median last frost of April 7 as the average last frost to get dates for Wilmington[6]. Hardy vegetables such as broccoli, lettuce and peas can go in as early as 2 to 4 weeks before that date, which is March 10 to March 24[6]. Semi-hardy vegetables such as beets, carrots and potatoes can go in as early as 2 weeks before it, from March 24 up to the median date[9]. Very tender vegetables such as tomatoes and peppers typically wait 2 or more weeks after it, so the earliest start is April 21[10].

  • Hardy (broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips): as early as 2 to 4 weeks before the median last frost (April 7) is March 10 to March 24[6]
  • Semi-hardy (beets, carrots, cauliflower, parsnips, potatoes, Swiss chard): as early as 2 weeks before the median last frost (April 7) is March 24, up to the median date itself[9]
  • Tender (snap beans, sweet corn, cucumbers, summer squash): from seed around the median last frost date, April 7[11]
  • Very tender (cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon): the earliest start, two weeks after the median last frost (April 7), is April 21[10]
Vegetable (CSU group) Plant from First harvest around
Broccoli (hardy)[12] Mar 10 May 14 (from transplants)
Cabbage (hardy)[12] Mar 10 Jun 3 (from transplants)
Kohlrabi (hardy)[12] Mar 10 Apr 29
Lettuce (hardy)[12] Mar 10 May 9
Onions (hardy)[12] Mar 10 Jun 28
Peas (hardy)[12] Mar 10 May 14
Radishes (hardy)[12] Mar 10 Apr 9
Spinach (hardy)[12] Mar 10 Apr 19
Turnips (hardy)[12] Mar 10 Apr 29
Beets (semi-hardy)[12] Mar 24 May 23
Carrots (semi-hardy)[12] Mar 24 Jun 2
Cauliflower (semi-hardy)[12] Mar 24 not listed
Parsnips (semi-hardy)[12] Mar 24 Jun 2
Potatoes (semi-hardy)[12] Mar 24 Jul 27
Swiss chard (semi-hardy)[12] Mar 24 May 23
Snap beans (tender)[12] Apr 7 Jun 6
Sweet corn (tender)[12] Apr 7 Jun 6
Cucumbers (tender)[12] Apr 7 Jun 1
Summer squash (tender)[12] Apr 7 May 27
Cantaloupe (very tender)[12] Apr 21 Jul 15
Eggplant (very tender)[12] Apr 21 Jun 20 (from transplants)
Peppers (very tender)[12] Apr 21 Jun 30 (from transplants)
Tomatoes (very tender)[12] Apr 21 Jun 25 (from transplants)
Winter squash (very tender)[12] Apr 21 Jul 30
Watermelon (very tender)[12] Apr 21 Jul 15
Spacing, depth and soil temperature (CSU Extension)
Vegetable Min. soil temp Depth Spacing Days to harvest
Broccoli[13] 40°F 1/2 in 18 in 65
Cabbage[13] 40°F 1/2 in 18 in 85
Kohlrabi[13] 40°F 1/2 in 7-9 in 50
Lettuce[13] 35°F 1/4 in 7-9 in 60
Onions[13] 35°F 1/4 in (seed), 1-2 in (sets) 4-6 in 110
Peas[13] 40°F 1 in 4-6 in 65
Radishes[13] 40°F 1/2 in 2-3 in 30
Spinach[13] 40°F 1/2 in 4-6 in 40
Turnips[13] 40°F 1/2 in 4-6 in 50
Beets[13] 40°F 3/4-1 in 4-6 in 60
Carrots[13] 40°F 1/4 in 2-3 in 70
Cauliflower[13] 40°F 1/2 in 18 in –
Parsnips[13] 35°F 1/2 in 5-6 in 70
Potatoes[13] 45°F – – 125
Swiss chard[13] 40°F 1 in 7-9 in 60
Snap beans[13] 55°F 1-1 1/2 in 6 in 60
Sweet corn[13] 50°F 1-1 1/2 in 12 x 30 in or 9 x 36 in 60-90
Cucumbers[13] 60°F 1 in 6 in trellised, 24-36 in untrellised 55
Summer squash[13] 60°F 1-1 1/2 in 36-48 in 50
Cantaloupe[13] 60°F 1-1 1/2 in 36-48 in 85
Eggplant[13] 60°F 1/4 in 18-24 in 60
Peppers[13] 60°F 1/4 in 15-18 in 70
Tomatoes[13] 50°F 1/4 in 24 in trellised 65
Winter squash[13] 60°F 1-1 1/2 in 36-48 in 100
Watermelon[13] 60°F 1-1 1/2 in 36-48 in 85

Hardiness zone

Zone 7b means an average annual extreme minimum temperature of 5°F to 10°F over 1991 to 2020[1]. The zone is based on the coldest night of each winter, not on summer heat or frost dates[14]. All of Wilmington's land area lies in ZIP code areas rated zone 7b[15].

Zone 7b: average annual extreme minimum temperature 5°F to 10°F (1991 to 2020)[1]. Modeled value at the city center: 8.7°F[1].

Share of the city's land area by ZIP code zone: zone 7b 100%[15].

All towns in zone 7b and what zone 7b means

Zone by ZIP code
ZIP code Zone Coldest night range
19801[15] 7b 5 to 10°F
19802[15] 7b 5 to 10°F
19809[15] 7b 5 to 10°F
19805[15] 7b 5 to 10°F
19806[15] 7b 5 to 10°F
19807[15] 7b 5 to 10°F
19803[15] 7b 5 to 10°F

Questions people ask

What growing zone is Wilmington, Delaware?
The 2023 USDA map puts the center of Wilmington in zone 7b[1]. By land area, 100% of the city lies in ZIP code areas rated 7b[15].
When is the last frost in Wilmington?
The median last spring frost is April 7, so in half of years the last frost comes after that date[2]. In 1 of 10 years it comes after April 24[2].
When is the first frost in Wilmington?
The median first fall frost is November 4, so in half of years it comes before that date[3]. In 1 of 10 years it comes before October 21[3].
When to plant tomatoes in Wilmington?
CSU Extension typically says very tender vegetables like tomatoes wait 2 or more weeks after the average last frost[10]. Using the median last frost, the earliest start is April 21[10].
How long is the growing season in Wilmington?
The growing season is at least 209 days in half of years[4]. It is at least 189 days in 9 of 10 years[4].

Facts and sources

  1. The 2023 USDA Plant Hardiness Zone Map puts the center of Wilmington, Delaware in zone 7b. Zone 7b means an average annual extreme minimum temperature of 5°F to 10°F over 1991 to 2020. The map's modeled value at the city center is 8.7°F. USDA zone map 2023 (PRISM, OSU)
  2. Last spring frost (32°F) at this station: in 9 of 10 years the last frost comes after March 26, in half of years after April 7, and in 1 of 10 years after April 24 (NOAA 1991 to 2020 normals). The median last frost date is April 7. NOAA Climate Normals 1991-2020
  3. First fall frost (32°F) at this station: in 1 of 10 years the first frost comes before October 21, in half of years before November 4, and in 9 of 10 years before November 19 (NOAA 1991 to 2020 normals). The median first frost date is November 4. NOAA Climate Normals 1991-2020
  4. Growing season (days between the last spring and first fall 32°F frost) at this station: at least 189 days in 9 of 10 years, at least 209 days in half of years, and at least 229 days in 1 of 10 years. NOAA Climate Normals 1991-2020
  5. Frost dates on this page come from NOAA climate normals for the Wilmington Porter Rsch weather station (USC00079605), 2.7 miles from the center of Wilmington at 270 feet, using 29 years of records from 1991 to 2020. NOAA Climate Normals 1991-2020
  6. Colorado State University Extension's vegetable planting guide (written for Colorado) groups broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips as hardy vegetables, with this rule: as early as 2-4 weeks before the average last... CSU Extension GardenNotes #720
  7. Hard freeze (28°F) at this station: the median last spring date is March 29 and the median first fall date is November 15. NOAA Climate Normals 1991-2020
  8. At this station the low reached 32°F or colder in 100% of years from 1991 to 2020, and 28°F or colder in 100% of years. NOAA Climate Normals 1991-2020
  9. Colorado State University Extension's vegetable planting guide (written for Colorado) groups beets, carrots, cauliflower, parsnips, potatoes, Swiss chard as semi-hardy vegetables, with this rule: as early as 0-2 weeks before the average last spring frost.... CSU Extension GardenNotes #720
  10. Colorado State University Extension's vegetable planting guide (written for Colorado) groups cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon as very tender vegetables, with this rule: typically 2 or more weeks after the average last... CSU Extension GardenNotes #720
  11. Colorado State University Extension's vegetable planting guide (written for Colorado) groups snap beans, sweet corn, cucumbers, summer squash as tender vegetables, with this rule: from seed around the average last spring frost; cucumber and summer squash... CSU Extension GardenNotes #720
  12. GardenFacts calculation: earliest planting date plus CSU days to harvest (table on this page), from the station's median last frost. NOAA Climate Normals 1991-2020
  13. CSU Extension vegetable table: soil temperature, depth, spacing, days to harvest (table on this page). CSU Extension GardenNotes #720
  14. USDA hardiness zones are based on the average annual extreme minimum winter temperature (the coldest night of each winter, averaged over 1991 to 2020 for the 2023 map), not on summer heat or frost dates. Each zone spans 10°F and each half zone (a or b)... USDA Plant Hardiness Zone Map
  15. Wilmington, Delaware overlaps 7 ZIP code areas. By land area, 100% lies in ZIP code areas rated zone 7b. USDA zone map 2023 (PRISM, OSU)

Frost dates are probabilities from 1991 to 2020 weather records at one NOAA station, not a forecast. Any year can be earlier or later. The hardiness zone describes the average coldest winter night, not frost dates or summer heat. Spots inside the city can differ (ZIP table). Planting rules come from Colorado State University Extension's guide, written for Colorado. A local extension office may give dates tuned to the area. Planting and harvest dates marked GardenFacts calculation are simple arithmetic from the facts above, not advice from the source.

Hardiness zone data: USDA Plant Hardiness Zone Map (2023), USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu, accessed October 30, 2026. This is not the official USDA map. Frost data: NOAA NCEI U.S. Climate Normals 1991-2020. Planting rules: Colorado State University Extension.