Sow hardy Asian greens such as bok choy, tatsoi and mizuna outdoors in early spring, around the last spring frost dates for the Wilmington reference station, and again in late summer so they mature before the first fall frost. Delaware gives you two good windows, and the fall one is usually the better of the two. The details below show how to place each one.
The short answer for Delaware
Sow cold-tolerant Asian greens outdoors from early April, and sow a second round in late summer so the plants finish growing before the first fall frost arrives. The reference frost dates for Delaware are April 3 to April 14 for the last spring frost and October 26 to November 7 for the first fall frost.
Those dates come from the NOAA NCEI 1991-2020 Climate Normals for the Wilmington airport station. Each one is a probability of a 32°F freeze, not a promise. The band covers dates where the chance of that freeze falls between 30 and 70 percent. Inside the April window, a freeze is still a coin-flip-type risk. Outside it, the odds shift sharply one way or the other.
The airport is a warm spot. NOAA’s station data describes one location, and suburban and rural gardens typically see the last spring frost later and the first fall frost earlier, often by one to two weeks, and more at elevation. Treat the figures as the reference-city case, not a guarantee for your yard.
| Season | Reference-city frost band | How to use it |
|---|---|---|
| Spring sowing | Last spring frost: April 3 to April 14 | Direct-sow the hardiest greens around this band. Tender or heat-hungry types wait until the frost risk has clearly passed. |
| Fall sowing | First fall frost: October 26 to November 7 | Count backward from this band by the days to maturity on the seed packet, then add a week or two of cushion for a rural or elevated site. |
This page does not have a Delaware-specific summer heat figure, so it does not give an exact last-sow date for spring. Instead, use the seed packet. Greens that bolt in long, warm days are better sown early, and a spring sowing that stretches into hot weather is the one most likely to go to seed. For the choice of types, see The Best Asian Greens for Delaware. For the wider picture, start with Growing Asian Greens in Delaware.
What will not work here
Sowing everything on one spring date fails first. A bed seeded in the first days of April can meet a freeze, since the reference band itself runs to April 14 and rural yards run later. Hardy greens shrug off a light frost once up. Tender seedlings and anything started under a warm spell do not.
Late spring sowings fail in a different way. Delaware summers are hot and humid, and the heat arrives soon after the last frost band. Asian greens sown too late in spring run out of cool days, bolt, and turn bitter before the heads fill out. Gardeners who treat April as a gentle, open-ended window get a row of flower stalks.
Winter is the third trap. The mean daily minimum of the coldest month at Wilmington is 25.6°F. That is the average low, not the record, so many nights in the coldest month fall well below freezing, and some far below the average. Tender bok choy planted in the fall does not carry through to spring in an open bed. Hardier greens such as tatsoi or mizuna can sometimes persist under a row cover, but plan on fall harvests rather than treating winter survival as reliable.
Last, fall sowing too late. A late-summer seeding that lands near or after the first fall frost band, October 26 to November 7, leaves seedlings small going into the cold. Shorter days slow growth in fall, so a plant that needs 45 days in spring needs a longer runway in October. Count back with room to spare.
The lesson is that Delaware’s season is long enough to grow Asian greens twice a year, but not forgiving enough to sow them on a single fixed date. Humid summers also invite crowding problems. Tight rows hold moisture on leaves and encourage rot, so give plants the spacing the packet recommends and do not squeeze in extra seed.
What changes across Delaware
Delaware is not one garden. The USDA Plant Hardiness Zone Map 2023 (built on 1991-2020 normals) places the state in zones 7a to 8a. That is a spread, and there is no single answer for the whole state. The USDA zone rests on one variable only, the average annual extreme minimum temperature, so it tells you about winter survival and says little about when to sow.
A gardener in the cooler northern part of the state should lean toward the later end of spring sowing and the earlier end of fall sowing. A gardener in the warmer southern or coastal part may get a longer fall season. Frost still decides the cutoff, so rely on local frost dates rather than the zone number.
Pay attention to microclimate within your own county, because the airport’s numbers do not describe low spots where cold air pools, or open rural fields. The caution on the frost data is clear: one to two weeks later in spring and earlier in fall is common away from the airport, and more at elevation.
Find your own zone on the USDA Plant Hardiness Zone Map rather than guessing from a neighbor’s garden. Use the zone to judge whether a plant can live through winter, and use the frost dates to schedule sowing. They answer different questions.
Where to check this for your own county
A county recommendation beats a state one, and this page is the state one. For local advice, go to University of Delaware Cooperative Extension, the state’s land-grant extension service. Delaware has only three counties, so the local office and agents are within reach for almost every gardener.
Look for two things there. First, a local vegetable planting calendar that gives sowing dates for your county, ideally for cool-season crops such as greens. Second, any variety trials run in your county, which show which Asian greens held up to local heat, bolting and disease.
This page does not have a Delaware calendar built specifically for Asian greens, and it does not borrow one from another state. The extension calendar in our source list is a Clemson tall fescue lawn calendar from South Carolina. It is a different crop in a different state, so it does not belong in a Delaware sowing plan. The lesson from it is only that extension services publish calendars per crop, so look for the one that matches what you are growing.
If the extension site lacks a greens-specific calendar, a general cool-season vegetable calendar for your county will serve as a starting point. Pair it with your own frost observations from the previous year.
Checking this against your own garden
Your own observations outrank every date on this page. Three are worth watching.
- Soil warmth by feel. Push a hand into the bed in early spring. Soil that feels cold and sticky, or stays wet in a clump, is not ready, and a bed that crumbles and feels cool rather than icy is. Comparing a sunny bed with a shaded corner shows how much your site differs from the reference city.
- The first male catkins on nearby trees. When male flowers start shedding pollen on trees around your yard, spring has turned for real. Note the date each year. It tells you how your yard runs compared with the airport figures, and whether your neighborhood runs early or late.
- The first true leaves on your seedlings. The first pair after the seed leaves shows how quickly your bed grows. A slow first sowing means you should sow earlier next fall, and fast growth gives you spare weeks.
Write down what you see in a notebook. Two seasons of notes are worth more than any general calendar, including this one.
Common questions
Can I sow Asian greens before the last spring frost in Delaware?
Hardy types such as tatsoi, mizuna and some bok choy can go in around the frost band, since they tolerate a light freeze once established. The reference band for the last spring frost is April 3 to April 14, and rural yards often run one to two weeks later, so sow a few seeds first and hold back the rest.
Is fall better than spring for Asian greens in Delaware?
For many gardeners, yes. Spring plantings run into heat and bolt, while fall plantings mature in cooling weather. The first fall frost band is October 26 to November 7 at the reference station, which gives a long runway if you sow in late summer.
Will Asian greens survive a Delaware winter?
Not reliably in an open bed. The mean daily minimum of the coldest month is 25.6°F at Wilmington, and Delaware sits in USDA zones 7a to 8a. Hardier greens may persist under a row cover, but tender bok choy should be harvested before hard freezes.
Do the frost dates here apply to my yard?
They describe the Wilmington reference station only. Suburban and rural gardens typically see the last spring frost later and the first fall frost earlier, often by one to two weeks, so check with your county extension office.