Asian greens grow well in Pennsylvania in two windows: early spring and late summer into fall. The fall window is the better one. Bok choy, mizuna, tatsoi and their relatives like cool weather, so spring sowings race against summer heat while late-summer sowings mature as nights cool. At the Philadelphia reference station the first fall frost averages November 5 to November 16, and that date sets how late you can sow.
When the soil is warm enough in Pennsylvania
The spring question starts with the last frost. At the Philadelphia reference station, the 30 to 70 percent probability band for a 32 F freeze runs from March 29 to April 6, according to NOAA’s 1991-2020 U.S. Climate Normals. Those dates are odds. A late freeze can still arrive after them, so keep a sheet of row cover handy.
Philadelphia is the mildest corner of the state. The northern tier and the Alleghenies run two to four weeks later in spring. The USDA Plant Hardiness Zone Map (2023) spans zones 5a to 7b across Pennsylvania, so a gardener near the Maryland line and one near the New York line are working with different calendars.
The frost date stands in for something else. Seeds respond to soil, and soil temperature lags behind air temperature. A mild week in late March can leave the ground cold a few inches down, and the soil only catches up after the frost risk has eased.
How do you know the soil is ready for Asian greens?
Start with workability. Grab a handful from the bed. If it crumbles, it is ready. If it smears or forms a wet ball, wait. A soil thermometer pushed in a couple of inches, read in the morning, tells you more than the calendar does.
Asian greens are cool-season crops, so they sprout in soil that would rot a bean seed. The earliest types can go in as soon as the bed is workable, with row cover over them. The trouble with a spring sowing comes later. Young plants that sit through a long cold spell and then meet sudden warmth may bolt, sending up a flower stalk instead of making leaves. Sow in the cooler part of the spring window and give the crop a shield against late freezes.
Types matter more than names here. Quick baby-leaf greens such as mizuna, tatsoi and komatsuna tolerate an early start better than heading napa cabbage, which wants a long cool stretch. For the varieties that have been trialled in your part of the state, ask Penn State Extension.
How long the season lasts here
The Philadelphia reference station’s frost-free season runs from the mean last spring frost (March 29 to April 6) to the mean first fall frost (November 5 to November 16), depending on which ends of the two bands you pair.
That is a generous window, and it allows two sowings. The first goes in as early spring soil allows and gets harvested before summer heat. The second goes in from mid to late summer and is the one that pays off, because the crop grows into cooler days. The general guide to growing Asian greens covers the plants themselves. A succession sowing guide covers the spacing of repeat plantings, and every couple of weeks is the usual rhythm for leafy types.
For the fall sowing, work backward. Take the first-frost date, read the days to maturity on the packet (counted from sowing for seeds put straight in the ground), and add a cushion. Growth slows as days shorten, so a crop that would need five weeks in July may need noticeably longer in October. Sowing a few days too early costs little. Sowing a week too late can leave you with a bed of small plants waiting on a freeze.
The window shrinks as you go north and uphill. Where the last frost comes two to four weeks later than in Philadelphia and the fall frost tends to come earlier, the spring sowing may be the only chance for some types. Whether to transplant also changes. Where the season is short, transplants started indoors buy time, but Asian greens dislike disturbed roots and may bolt if the root ball is damaged or the plant is stressed. Check that the roots have filled the cell without circling, and handle them gently. Where the season is long, direct sowing is easier and the second sowing makes up for any loss.
Gardeners comparing climates may find it useful to read how the same crops run in Colorado and in Illinois, where the spring-to-fall rhythm is different again.
Heat and water in Pennsylvania
This family belongs to the second half of the year, so the numbers that matter most are the first frost and the winter low. Summer heat decides how well a spring crop holds. A hot spell is a bolting signal for most Asian greens, and the southeastern part of the state, with its warm, humid summers, gets enough of them to cut a spring harvest short. In the cooler northern tier and at higher elevations, the summer is milder, so heat is a smaller worry. Damp weather there brings its own trouble: downy mildew and leaf spots on crowded plants, slugs under wet mulch, and slow growth when the sun is scarce.
Water works the same way. Brassicas want even moisture, and a dry spell followed by a downpour causes tipburn and splitting in heading types. Drip lines or soaker hoses keep leaves dry, and morning watering lets foliage dry before evening. A layer of mulch keeps the soil cooler at the root, which helps delay bolting in July and August. Wider spacing than you think you need gives air room to move, a real defense against mildew in a wet year.
Can Asian greens survive a Pennsylvania winter?
In the fall, the first frost date sets how late a sowing can still finish. At Philadelphia that is November 5 to November 16. Most Asian greens handle a light frost, and some leaf types sweeten after one. A hard freeze is another matter and ends the crop for the least hardy types.
The winter low decides the rest. The mean daily minimum of the coldest month at the Philadelphia reference station is 26.0 F (NOAA’s 1991-2020 normals). Most midwinter nights there dip below freezing without going deep. That is the range where the hardiest greens, such as tatsoi and mizuna, can stand through the cold under a low tunnel or heavy row cover, though they stop growing and the harvest is limited to what survived. Without cover, the first hard freeze usually ends them. Northern and mountain gardeners in colder zones should treat cover as the minimum, not the bonus, and plan for loss.
One more point that affects every bed. Turnip and rutabaga are brassicas, as are cabbage, kale and mustard, and Asian greens belong to the same family. They share pests and diseases such as flea beetles, cabbage worms and clubroot. A gardener who follows bok choy with cabbage, or puts a turnip crop where mustard grew, has rotated nothing. Keep the whole family out of a bed for several years, and use row cover over seedlings to block flea beetles before they find them.
Which Asian greens suit Pennsylvania
Choose by type, and let the local climate break ties. The table lays out how the main types line up against what the state throws at them.
| Type | Best window | Main risk |
|---|---|---|
| Baby-leaf greens (mizuna, tatsoi, komatsuna) | Early spring and fall | Bolting in a warm spell |
| Bok choy and other pak choi | Late summer sowing for fall | Bolting after a cold snap in spring |
| Napa cabbage | Late summer sowing for fall | Disease and rot in a wet fall |
| Mustard greens | Spring and fall | Flea beetles, strong flavor in heat |
A short season, as in the northern tier and the Alleghenies, favors the earliest types: baby-leaf greens and small, quick bok choy that finish before the window closes. Heading napa cabbage asks for more time and is a poor bet where fall frost comes early.
Where summers run warm, as in the southeast, the better choice is a type that tolerates warmth, given airflow and shade at the root. Loose-leaf greens and mustards cope better than tight heads. Mulch, spacing and a sheet of shade cloth in midsummer help more than any seed choice.
Humidity makes disease resistance the first thing to look for. Check the seed packet or catalog for resistance to downy mildew and similar problems, and pull any plant that shows a soft patch, a weeping spot or a moldy crown. If you hold harvested heads, inspect them the same way: a soft patch, a weeping spot or a moldy crown ends the question, and the head goes to the compost.
No variety is named here, because the recommendation that counts comes from trials run close to your own garden, and a variety that does well near Philadelphia can behave very differently on a plateau in the north. Penn State Extension and your county office know which ones have been tested for your area. The extension service is the place to ask.
Common questions
When should I sow bok choy in Pennsylvania?
Two times work: early spring once the soil is workable, and mid to late summer for a fall crop. The fall sowing usually does better. Count back from the first frost, which averages November 5 to November 16 at Philadelphia and comes earlier in the north and at elevation.
Why do my Asian greens bolt?
Heat is the usual cause, along with long days and stress. A cold spell on young plants can also trigger it. Sow in cooler weather, keep the soil evenly moist, mulch to cool the roots, and harvest early.
Can Asian greens stay in the garden through winter?
The hardiest types can, under a low tunnel or row cover, in the milder parts of the state. Where winters are colder, expect to lose most of them at the first hard freeze unless they are protected.
Can I plant Asian greens where cabbage grew?
No. Asian greens are brassicas and share pests and diseases with cabbage, kale, mustard, turnip and rutabaga. Rotate them to a bed that has been free of the whole family for several years.