Seed Starting Calendar for Delaware

Count back from the median last frost where you garden. At Georgetown (Georgetown Sussex County Airport) that date is April 4, so for spring 2027 onions start indoors Dec 27 to Jan 10, peppers Feb 7 to Feb 21 and tomatoes Feb 14 to Feb 28. Across Delaware's 7 NOAA stations the median last frost runs from Mar 29 to Apr 11 for the middle 90 percent, so a garden near Greenwood 2NE starts later than one near Lewes.

It depends on the station. The earliest median last spring freeze in Delaware is March 29 at Lewes; the latest is April 11 at Greenwood 2NE. A median is a coin flip: at Georgetown the last 32°F freeze comes after April 4 in half of years, and has passed by April 16 in 9 of 10 years (NOAA 1991 to 2020 normals).

UNH Extension sets tomatoes out 1 to 2 weeks after the last frost, which at Georgetown is Apr 11 to Apr 18 in 2027. Tomatoes are frost tender, so the date to watch is April 16, when 9 of 10 springs at Georgetown have had their last 32°F night. Hardening off starts two weeks before setting out (Mar 28 to Apr 11).

University of Delaware Cooperative Extension publishes planting months by region (New Castle County, northern Delaware). For New Castle County, northern Delaware, tomatoes go in during May. Seeds for transplants go in 4 to 10 weeks ahead of those months, depending on the crop.

UNH Cooperative Extension's method works in any state with a spring frost: "Using a calendar, mark the date and count backwards the number of weeks the seed takes to grow from sowing. This will be the date you will start your seeds." The weeks for each crop come from UNH and Colorado State, and the frost date comes from the NOAA station nearest you in Delaware.

UNH Extension gives 8 to 10 weeks from seed to transplant for both, and sets peppers out 2 weeks after the last frost and eggplant 2 to 3 weeks after, so the sowing date is 6 to 8 weeks before the median last frost. At Georgetown that is Feb 7 to Feb 21 for peppers.

About two weeks. University of Missouri Extension: "Hardening should be started about two weeks before planting in the garden." University of Minnesota Extension adds that seedlings should go out on a cloudy day or in the late afternoon.

Delaware is compact: Dover and Georgetown share a median last frost around Apr 4 and Wilmington follows around Apr 7, so one statewide seed calendar fits nearly every garden. Each station carries its own dates: Dover Apr 4 and Wilmington Apr 7 at the median.