Delaware weather and outdoor projects
Delaware has a humid climate with hot summers and fairly mild winters for the Mid-Atlantic, moderated by Delaware Bay and the Atlantic. Rain is spread through the year, and summer brings humid days with afternoon storms.
Spring and early fall give the best combinations of mild temperatures and lower humidity for deck staining and exterior painting. Coastal areas in Sussex County see salt air and wind that are hard on finishes, so a good deck stain and regular maintenance pay off. Winter freezes are common but usually short, and concrete poured from December to February needs protection on cold nights.
Frost dates in Delaware
In Wilmington, the median last spring freeze (32°F) is around April 7 and the median first fall freeze is around November 1, a frost-free season of about 209 days.
How Delaware compares with other states
Wilmington is tied for the 7th-longest deck staining season of the 50 state main stations (5 good months). Wilmington is tied for the 20th-most rainy days of the 50 state main stations (75 a year with 0.1 in or more). Wilmington is tied for the 21st-fewest days at 90°F or hotter of the 50 state main stations (22 a year).
| Measure (Wilmington) | Value | Rank, highest first |
|---|---|---|
| Deck staining season | 5 good months | 7th of 50 |
| Frost-free season | 209 days | 25th of 50 |
| Freezing nights | 92 a year | 26th of 50 |
| Rainy days | 75 a year with 0.1 in or more | 20th of 50 |
| Days at 90°F or hotter | 22 a year | 29th of 50 |
Best time to stain a deck in Delaware
In Wilmington, the most reliable months are May–September. April and October can also work on the right days (average highs Apr 64°F, Oct 67°F). December–March is too cold, with average highs around 46°F. In November, nights average about 37°F, too cold for the coating to dry and cure overnight. In April and October, nights average about 45°F, so finish early on mild days and check the overnight low.
Best time to paint outside in Delaware
In Wilmington, the most reliable months are May–October. March–April and November can also work on the right days (average highs Mar 53°F, Apr 64°F, Nov 56°F). December–February is too cold, with average highs around 44°F. March and November are cool, with highs around 54°F, so choose the warmest afternoons. In April, nights average about 44°F, so finish early on mild days and check the overnight low.
Best time to pour concrete in Delaware
In Wilmington, the most reliable months are May–October. April can also work on the right days (average highs Apr 64°F). November–March averages about 18 nights a month at or below 32°F, so fresh concrete needs blankets or heated enclosures. April brings about 2 freezing nights a month, so pick a mild spell and keep curing blankets on hand.
Best time to seal a driveway in Delaware
In Wilmington, the most reliable months are May–September. April and October can also work on the right days (average highs Apr 64°F, Oct 67°F). November–March is too cold, with average highs around 48°F. April and October are cool, with highs around 66°F, so choose the warmest afternoons.
Best time to fertilize or treat a lawn in Delaware
In Wilmington, the most reliable months are April–June and August–October. March, July and November can also work on the right days (average highs Mar 53°F, Jul 87°F, Nov 56°F). December–February is too cold, with average highs around 44°F. March and November are cool, with highs around 54°F, so choose the warmest afternoons. July is hot, with highs near 87°F, so start early and keep out of full afternoon sun.
Monthly weather in Wilmington
| Month | Avg high | Avg low | Wet days* | Rain | Freezing nights |
|---|---|---|---|---|---|
| January | 41°F | 26°F | 6 | 3.2 in | 24 |
| February | 44°F | 27°F | 6 | 2.8 in | 21 |
| March | 53°F | 34°F | 7 | 4.2 in | 14 |
| April | 64°F | 44°F | 7 | 3.5 in | 2 |
| May | 74°F | 53°F | 7 | 3.6 in | 0 |
| June | 82°F | 63°F | 7 | 4.7 in | 0 |
| July | 87°F | 68°F | 7 | 4.4 in | 0 |
| August | 85°F | 67°F | 6 | 4.0 in | 0 |
| September | 79°F | 59°F | 6 | 4.4 in | 0 |
| October | 67°F | 47°F | 6 | 3.7 in | 1 |
| November | 56°F | 37°F | 6 | 3.1 in | 10 |
| December | 46°F | 30°F | 7 | 3.9 in | 20 |
*Days with 0.1 inch of rain or more; column notes.
Source: NOAA NCEI U.S. Climate Normals 1991–2020 for WILMINGTON NEW CASTLE CO AP. See how the ratings work and how late in fall you can stain, paint or seal.
Frequently asked questions
When is the best time to stain a deck in Delaware?
In Wilmington, May–September.
When is the last frost in Delaware?
Wilmington: around April 7.
Can you pour concrete in winter in Delaware?
Yes, with cold-weather practices: Wilmington averages about 65 freezing nights from December to February, so fresh concrete needs insulated blankets, a heated enclosure or an accelerated mix, and must not freeze in the first 48 hours. Many homeowners wait for spring.
What months are best for sealing a driveway in Delaware?
In Wilmington, May–September.