Sow Asian greens twice a year in Pennsylvania: once in early spring, once from late summer into early fall. The fall sowing is the more dependable of the two. Exact dates shift by weeks depending on where you garden, because the state runs from the Philadelphia suburbs to the northern tier and the Allegheny plateau.
The short answer for Pennsylvania
Start spring sowings about four weeks before the last spring frost, as soon as the soil is workable, and start fall sowings roughly eight to ten weeks before the first fall freeze. At the Philadelphia reference station, NOAA’s 1991-2020 U.S. Climate Normals put the last spring 32°F freeze between March 29 and April 6. They put the first fall freeze between November 5 and November 16.
Those dates are probabilities of a 32°F freeze. Each range is the band where the odds fall between 30 and 70 percent. Some years a freeze arrives after the spring window closes, and some years it holds off past the fall one. Asian greens such as bok choy, tatsoi, mizuna and komatsuna shrug off a light frost, so a late freeze rarely ruins a planting once the seedlings have their first true leaves.
Philadelphia is the mildest corner of the state. The northern tier and the Alleghenies run two to four weeks later in spring, which puts their last frost roughly from mid-April to early May. The table shows the windows that follow from that. Treat them as starting points.
| Sowing | Southeast (Philadelphia area) | Northern tier and Alleghenies |
|---|---|---|
| Spring | Early March to late April | Early April to mid-May |
| Fall | Mid-August to late September | Early August to early September |
How long do Asian greens take from sowing?
Seed packets commonly list around 45 to 50 days from sowing for full-size bok choy, and a few weeks for baby leaves of mizuna or tatsoi. Count back from your first fall freeze and add a week or two, because growth slows as days shorten. A bed sown in mid-August in the southeast has time to reach full size. A bed sown in late September is for baby leaves, and a low tunnel will stretch the harvest.
For which types suit which window, see The Best Asian Greens for Pennsylvania. The broader picture of the crop is in Growing Asian Greens in Pennsylvania.
What will not work here
Sowing heading types in late spring fails. Napa cabbage and full-size bok choy sown in May run straight into June’s long days and summer heat, and they bolt before they size up. Once the center stalk elongates, the leaves turn bitter and the plant is finished. Spring is for fast, small harvests: baby leaves, tatsoi rosettes, mizuna cut young. Anything that needs eight weeks of cool weather belongs in the fall window.
Sowing in the cold, wet ground of early March in the north fails too. Seed sitting in soil in the 30s and low 40s rots or germinates unevenly, and a thin, ragged stand invites weeds. The southeast can start in early March in a good year. The northern tier is usually better off waiting until the beds have thawed, drained and warmed a bit, which in many years means April.
Pennsylvania summers are humid, and that punishes tight spacing. Asian greens grown shoulder to shoulder hold moisture in the canopy, and that favors downy mildew and slugs. Thin bok choy to 6 to 8 inches for full heads, and give baby-leaf rows enough air that the foliage dries after a morning dew. Flea beetles are the other spring problem, since they pepper young leaves with tiny holes, and a light row cover over the bed from sowing day is the standard answer.
Watering once a week is not enough either, even in a humid state. Asian greens have shallow roots, and a dry stretch of ten days in July or August can stall a fall planting at the seedling stage. The fall window opens in the hottest part of the year, so the seedbed needs light watering every day or two until the plants are up, and a layer of shade cloth or a spot in afternoon shade helps. Lettuce-style germination problems also show up here: seed sown into soil much above 85°F often fails to sprout.
Winter is the last limit. The mean daily minimum of the coldest month at Philadelphia is 26.0°F. Hardy greens like tatsoi and mizuna can ride that out under a row cover or low tunnel, and bok choy usually cannot. Farther north, where winter lows run well below that, plan on the fall crop ending by midwinter.
What changes across Pennsylvania
The USDA Plant Hardiness Zone Map (2023 edition, built on 1991-2020 normals) places Pennsylvania in zones 5a through 7b. No single sowing date can serve that range.
Zone numbers measure winter cold, which matters most for overwintering. Sowing dates depend on frost timing, so use the zone as a rough guide to how far to shift. In the colder end of the range, expect a spring frost two to four weeks later than Philadelphia’s and a fall freeze that arrives earlier. The practical result is a shorter fall runway. Someone in the northern tier should sow fall crops in early August and favor the faster types, such as mizuna, tatsoi and baby bok choy, over large heading varieties.
Elevation works the same way. Valleys can hold cold air on clear spring nights and frost can hit after surrounding ridges have cleared, while a south-facing slope warms days sooner. Cities and the Delaware valley run warmer, which can let the fall crop go later under cover.
To see where your garden falls, look up your location on the USDA Plant Hardiness Zone Map and compare it with the zones around you. Then shift the table above toward the northern column if you are in the colder range, and toward the southeast column if you are in the milder one.
Where to check this for your own county
Your state’s land-grant extension service is the place to confirm dates. In Pennsylvania that is Penn State Extension, which has a county office serving each part of the state.
Look for three things on the site or at the county office:
- A vegetable planting calendar written for your region, with spring and fall sowing dates for cool-season crops.
- Local frost date information for your county, ideally from a weather station near you.
- Variety trial results for Asian greens or other brassica crops, which show what has actually held up to local pests and weather.
A county recommendation beats a state one. County staff know which valleys frost late, which soils drain slowly and which pests are active that year. The windows here are a statewide guide built from one reference station, and the real dates for your county can sit a couple of weeks either side of them. If the county office and the table disagree, go with the county.
Checking this against your own garden
Your own observations outrank any calendar. Three are worth watching.
First, the feel of the soil. Push your bare hand a few inches into the bed in the morning. If the soil feels cold to your touch, seeds will sit and may rot. Soil that feels cool but not biting is ready for hardy greens. Beds along a south wall or in raised boxes reach that point days to weeks before a shaded, low-lying bed.
Second, the plants growing around the yard. Forsythia in full bloom is an old marker that the ground has loosened and warmed enough for cool-season seed. If your forsythia blooms a week or two later than a neighbor’s down the hill, shift your spring sowing by the same amount.
Third, the pace of your seedlings. Note how long a sowing takes to show its first true leaves, which are the ones after the rounded seed leaves. Seedlings that stall at that stage point to soil that is too cold in spring or too hot and dry in late summer. Once you spot a central stalk starting up in a spring planting, that bed has hit its heat limit, and next year’s sowing should go in earlier.
A notebook with sowing dates and these three observations will give you a calendar tuned to your own yard.
Common questions
Can I sow Asian greens in Pennsylvania in summer?
Mid-summer sowing is the hardest time. Soil heat can stop seed from sprouting, and plants that do come up bolt or get eaten by flea beetles. Wait for the August fall window, or sow in a shaded bed with daily watering.
Do I need to wait for the last frost to sow in spring?
No. Hardy Asian greens go in about four weeks before the last frost, once the soil can be worked. A light frost will not hurt seedlings that have their first true leaves, and a row cover adds protection on colder nights.
When is the last good fall sowing date?
In the southeast, baby-leaf sowings still work into late September, and a low tunnel helps after that. In the northern tier, aim to finish by early September. Full-size heads need the earlier dates.
Can Asian greens overwinter in Pennsylvania?
Tatsoi and mizuna sometimes do under a row cover or tunnel in the milder southeast, where the coldest month’s mean daily minimum is 26.0°F at Philadelphia. In colder zones, expect them to die back, and treat them as a fall crop.