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Frost dates and planting calendar for Dover, 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 4[2]
Median first fall frost
Nov 4[3]
Growing season, median
214 days[4]

Dover, Delaware is in USDA hardiness zone 7b[1]. The median last spring frost is April 4, which means that in half of years the last frost comes after that date[2].

Frost dates

JanFebMarAprMayJunJulAugSepOctNovDecLast spring frost: 9 in 10 years after Mar 22, half of years Apr 4, 1 in 10 years after Apr 17Last frostmedian Apr 4First fall frost: 9 in 10 years before Nov 18, half of years Nov 4, 1 in 10 years before Oct 23First frostmedian Nov 4Frost riskHardyHardy vegetables: plant Mar 7 to Mar 21Mar 7 to Mar 21Semi-hardySemi-hardy vegetables: plant Mar 21 to Apr 4Mar 21 to Apr 4TenderTender vegetables: plant around Apr 4around Apr 4Very tenderVery tender vegetables: plant from Apr 18from Apr 18
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 come from NOAA climate normals for the Dover weather station, using records from 1991 to 2020[5]. They are odds and not promises. In 9 of 10 years the last spring frost comes after March 22, and in 1 of 10 years it comes after April 17[2]. In the fall, the median first frost is November 4, and in 1 of 10 years the first frost comes before October 23[3].

Frost Likely (9 in 10 years) Even odds (5 in 10) Unlikely (1 in 10)
Last spring frost (32°F)[2] after March 22 after April 4 after April 17
First fall frost (32°F)[3] before October 23 before November 4 before November 18
  • Hard freeze (28°F): median last spring date March 25, median first fall date November 16[7].
  • Frost-free growing season: at least 195 days in 9 of 10 years, 214 days in half of years and 234 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: Dover (USC00072730), 1.3 miles from the city center, 30 feet, 30 years of 1991 to 2020 records[5].

When to plant vegetables

Colorado State University Extension wrote its vegetable planting guide for Colorado[6]. We took the NOAA median last frost of April 4 as the average last frost[6]. Hardy vegetables such as lettuce, peas and spinach can go in as early as 2 to 4 weeks before it, which is March 7 to March 21[6]. Semi-hardy vegetables such as carrots and potatoes can go in as early as 2 weeks before it, from March 21[9]. Tender vegetables such as snap beans and sweet corn can be seeded around April 4[10]. Very tender vegetables such as tomatoes and peppers typically wait 2 or more weeks after the last frost, so the earliest start is April 18[11].

  • Hardy (broccoli, cabbage, kohlrabi, lettuce, onions, peas, radishes, spinach, turnips): as early as 2 to 4 weeks before the median last frost (April 4) is March 7 to March 21[6]
  • Semi-hardy (beets, carrots, cauliflower, parsnips, potatoes, Swiss chard): as early as 2 weeks before the median last frost (April 4) is March 21, up to the median date itself[9]
  • Tender (snap beans, sweet corn, cucumbers, summer squash): from seed around the median last frost date, April 4[10]
  • Very tender (cantaloupe, eggplant, peppers, tomatoes, winter squash, watermelon): the earliest start, two weeks after the median last frost (April 4), is April 18[11]
Vegetable (CSU group) Plant from First harvest around
Broccoli (hardy)[12] Mar 7 May 11 (from transplants)
Cabbage (hardy)[12] Mar 7 May 31 (from transplants)
Kohlrabi (hardy)[12] Mar 7 Apr 26
Lettuce (hardy)[12] Mar 7 May 6
Onions (hardy)[12] Mar 7 Jun 25
Peas (hardy)[12] Mar 7 May 11
Radishes (hardy)[12] Mar 7 Apr 6
Spinach (hardy)[12] Mar 7 Apr 16
Turnips (hardy)[12] Mar 7 Apr 26
Beets (semi-hardy)[12] Mar 21 May 20
Carrots (semi-hardy)[12] Mar 21 May 30
Cauliflower (semi-hardy)[12] Mar 21 not listed
Parsnips (semi-hardy)[12] Mar 21 May 30
Potatoes (semi-hardy)[12] Mar 21 Jul 24
Swiss chard (semi-hardy)[12] Mar 21 May 20
Snap beans (tender)[12] Apr 4 Jun 3
Sweet corn (tender)[12] Apr 4 Jun 3
Cucumbers (tender)[12] Apr 4 May 29
Summer squash (tender)[12] Apr 4 May 24
Cantaloupe (very tender)[12] Apr 18 Jul 12
Eggplant (very tender)[12] Apr 18 Jun 17 (from transplants)
Peppers (very tender)[12] Apr 18 Jun 27 (from transplants)
Tomatoes (very tender)[12] Apr 18 Jun 22 (from transplants)
Winter squash (very tender)[12] Apr 18 Jul 27
Watermelon (very tender)[12] Apr 18 Jul 12
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

The 2023 USDA map puts the center of Dover in zone 7b, which means an average coldest night of the year between 5°F and 10°F[1]. The zone is based on the coldest winter night and not on summer heat or frost dates[14]. Dover overlaps 3 ZIP code areas, and by land area 100% lies in 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: 7.7°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
19901[15] 7b 5 to 10°F
19904[15] 7b 5 to 10°F
19902[15] 7b 5 to 10°F

Questions people ask

What growing zone is Dover, Delaware?
The 2023 USDA Plant Hardiness Zone Map puts the center of Dover in zone 7b[1]. All of the city's land area lies in ZIP code areas rated 7b[15].
When is the last frost in Dover?
The median last spring frost at the Dover station is April 4, so in half of years the last frost comes after that date[2]. In 1 of 10 years it comes after April 17[2].
When to plant tomatoes in Dover?
CSU Extension says tomatoes typically go in 2 or more weeks after the average last frost, which gives an earliest start of April 18 when we use the median last frost[11]. CSU's guide was written for Colorado[11].
When is the first frost in Dover?
The median first fall frost is November 4, so in half of years the first frost comes before that date[3]. In 1 of 10 years it comes before October 23[3].
How long is the growing season in Dover?
The growing season between the last spring and first fall frost is at least 214 days in half of years[4]. It is at least 195 days in 9 of 10 years[4].

Facts and sources

  1. The 2023 USDA Plant Hardiness Zone Map puts the center of Dover, 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 7.7°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 22, in half of years after April 4, and in 1 of 10 years after April 17 (NOAA 1991 to 2020 normals). The median last frost date is April 4. 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 23, in half of years before November 4, and in 9 of 10 years before November 18 (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 195 days in 9 of 10 years, at least 214 days in half of years, and at least 234 days in 1 of 10 years. NOAA Climate Normals 1991-2020
  5. Frost dates on this page come from NOAA climate normals for the Dover weather station (USC00072730), 1.3 miles from the center of Dover at 30 feet, using 30 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 25 and the median first fall date is November 16. 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 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
  11. 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
  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. Dover, Delaware overlaps 3 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.