Frost dates for Wilmington, Delaware
In Wilmington, half of springs have had their last frost by April 7 (and 1 spring in 10 still has one after April 21), and half of falls have had their first frost by November 1, leaving about 209 frost-free days in a typical year. Here is how sure those dates are, what they mean for planting, and where they come from.
Frost dates for
Wilmington, Delaware
Last spring frost
April 7
Half of springs have their last frost by this date. For a safer bet, wait until April 21: only 1 spring in 10 has a frost after that.
First fall frost
November 1
Half of falls have their first frost by this date. In 1 fall in 10 it comes by October 19.
Growing season
209 days
Frost-free days in a typical year. 9 years in 10 get at least 186.
Hardiness zone
7b
2023 USDA map: the coldest night of winter averages 5°F to 10°F. On the 2012 map it was 7a, half a zone colder. All 15 ZIP codes within about 6 miles of the city's center are in zone 7b.
Stations near you disagree. NOAA's Wilmington New Castle Co Airport (6 miles away, at 80 feet above sea level), the one we used, gives a typical last frost of April 7 and a typical first frost of November 1. NOAA's Marcus Hook (8 miles away, at 10 feet above sea level) gives a typical last frost of March 30 and a typical first frost of November 16. So the typical last frost could fall anywhere from March 30 to April 7 and the typical first frost from November 1 to 16, depending on whether your garden is more like one or the other. Local terrain matters: hillsides, valley floors, water and city heat can change frost dates a lot over a few miles. Treat the dates here as a starting point, and compare with a nearby gardener or your county extension office.
Print a year planner for Wilmington
Frost risk through the year
How sure are these dates?
A frost date is a probability, not a promise. NOAA worked out, from 30 years of nightly lows, how often the last spring frost and the first fall frost fall on each date. The middle column is the typical year. The outer columns are the early and late years that come about once a decade.
| Early year 1 in 10 | Typical year 1 in 2 | Late year 1 in 10 | |
|---|---|---|---|
| Last frost in spring | March 26 | April 7 | April 21 |
| First frost in fall | October 19 | November 1 | November 15 |
The frost-free season between them runs 209 days in a typical year. In 1 year in 10 it is 228 days or longer, and in 1 year in 10 it is 186 days or shorter.
- Hard freeze (28°F): typically last on March 27 and first on November 14. It is a harder freeze than the 32°F frost line, cold enough to damage many garden plants; how hardy a crop is decides whether it comes through. (The National Weather Service's own hard-freeze threshold varies from office to office.)
- Frost possible (36°F at the station): typically last on April 21 and first on October 22. On clear, still nights the ground can be several degrees colder than the thermometer, so frost can form on plants when the official reading is in the mid-30s.
In 8 springs out of 10, the last frost in Wilmington comes between March 26 and April 21, a window of 26 days. That is narrower than at most NOAA stations (the typical window is 31 days), so the typical date is a steadier guide here than in most places.
Among Delaware's 7 NOAA stations with a frost every year, 14 percent have their typical last frost later than Wilmington does.
Planting calendar for Wilmington
These dates count from the typical last and first frosts, using the planting rules published by Colorado State University Extension (spring), Virginia Cooperative Extension (fall crops) and University of Minnesota Extension (garlic, where winters are hard). Weather in any one year can run early or late, so check the forecast before you plant tender crops.
| When | What to do | Why then |
|---|---|---|
| January | ||
| January 20 to February 17 | Broccoli and cabbage Start seeds indoors | 5 to 7 weeks before planting them out |
| February | ||
| February 3 to March 3 | Cauliflower Start seeds indoors | 5 to 7 weeks before planting out |
| February 17 to March 10 | Eggplant Start seeds indoors | 6 to 9 weeks before planting out |
| February 24 to March 10 | Peppers Start seeds indoors | 6 to 8 weeks before planting out |
| March | ||
| March 3 to 17 | Tomatoes Start seeds indoors | 5 to 7 weeks before planting out |
| March 10 to 24 | Peas, spinach, lettuce, radishes, onion sets, turnips Sow outdoors, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| March 10 to 24 | Broccoli and cabbage Plant out, as early as | hardy crops: 2 to 4 weeks before the typical last frost |
| March 24 to April 7 | Beets, carrots, potatoes, Swiss chard Plant outdoors, as early as | semi-hardy crops: up to 2 weeks before the typical last frost |
| March 24 to April 7 | Cauliflower Plant out, as early as | semi-hardy: up to 2 weeks before the typical last frost |
| April | ||
| April 7 | Snap beans, sweet corn, cucumbers, summer squash Sow outdoors around | tender crops: around the typical last frost date |
| April 21 | Tomatoes, peppers, eggplant Plant out from | very tender: 2 weeks or more after the typical last frost |
| April 21 | Melons, winter squash, pumpkins, lima beans Sow outdoors from | very tender: 2 weeks or more after the typical last frost |
| June | ||
| June 6 to 20 | Cabbage for fall Start seeds | set the plants out by July 25 |
| June 26 to July 10 | Broccoli for fall Start seeds | set the plants out by August 14 |
| August | ||
| August 5 | Snap beans for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| August 9 | Carrots for fall Last date to sow | 70 days to harvest, plus 2 weeks for slower fall growth |
| August 10 | Cucumbers for fall Last date to sow | 55 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| August 14 | Peas for fall Last date to sow | 65 days to harvest, plus 2 weeks for slower fall growth |
| August 15 | Summer squash for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth, plus 2 weeks because frost kills it |
| August 19 | Leaf lettuce and beets for fall Last date to sow | 60 days to harvest, plus 2 weeks for slower fall growth |
| August 29 | Turnips and kohlrabi for fall Last date to sow | 50 days to harvest, plus 2 weeks for slower fall growth |
| September | ||
| September 8 | Spinach for fall Last date to sow | 40 days to harvest, plus 2 weeks for slower fall growth |
| September 18 | Radishes for fall Last date to sow | 30 days to harvest, plus 2 weeks for slower fall growth |
| October | ||
| October 19 | Tomatoes, peppers, squash, melons, cucumbers Watch the forecast from | in 1 fall in 10 the first frost comes by this date; pick tender crops before a frost |
| November | ||
| November 21 to 28 | Garlic Plant cloves | one or two weeks after the typical first hard freeze (28°F), our reading of the first killing frost |
Want more insurance? Shift every spring date 14 days later. That plans around April 21, the date after which only 1 spring in 10 has a frost.
For spring bulbs such as tulips and daffodils, plant once the soil has cooled to about 50 to 55°F and keep going until a couple of weeks before the ground freezes. Our guide to fall planting explains how to tell.
Where these numbers come from
These dates come from NOAA's weather station Wilmington New Castle Co Airport (station USW00013781), 6 miles from the center of Wilmington. It sits at about the same elevation, 80 feet above sea level. NOAA rates this station's record as standard: at least 24 of the 30 years, with gaps filled from nearby stations.
The same station also gives the frost dates for Newark and Middletown.
Our ZIP code lookup matches these 10 ZIP codes to the same station, so they get the same dates: 08023, 08070, 19706, 19720, 19730, 19731, 19733, 19801, 19804, 19805. Hardiness zones are worked out separately for each ZIP code.
Nearby places
- Philadelphia, Pennsylvania: last frost around April 4, first frost around November 7 (30 miles away)
- Dover, Delaware: last frost around April 4, first frost around November 4 (40 miles away)
- Trenton, New Jersey: last frost around April 10, first frost around November 1 (55 miles away)
See frost dates across Delaware, or look up your own ZIP code for the station nearest you. Want the background? Read what a last frost date really means.