For most Pennsylvania gardens, the best Asian greens are the quick, cool-season ones: bok choy, tatsoi, mizuna, komatsuna and mustard greens, sown in early spring and again in late summer. Napa cabbage works as a fall crop only. Heat lovers like amaranth and water spinach need the warmest part of the state and a hot July. A few weeks of season separate Philadelphia from the northern tier, and that gap changes the plan.
The short answer for Pennsylvania
Build the bed around fast leafy types: baby bok choy, tatsoi, mizuna, komatsuna and mustard greens, grown in spring and again from late summer into fall. Add napa cabbage and other heading types for fall only, and treat the heat lovers as an optional summer extra. If you grow only one season, make it fall.
At the Philadelphia reference station, the last spring freeze falls between March 29 and April 6. The first fall freeze falls between November 5 and November 16. Both ranges describe the chance of a 32°F freeze. Across each window the odds sit in the 30 to 70 percent band, so a freeze on either side of those dates is ordinary. Philadelphia is also the mildest corner of the state. The northern tier and the Alleghenies run two to four weeks later in spring.
Cool-season types win because most Asian greens are brassicas. They germinate in cool soil, shrug off light frost and grow fast. Packet days count from sowing for these direct-sown crops. Full-size bok choy and choy sum take longer, closer to the point where the heads have filled out. Spring is the shorter of the two windows because rising heat and lengthening days push the plants to bolt in June. Fall runs the other way: soil cools, days shorten, and a touch of frost sweetens the leaves.
| Type | Examples | Best window | Role in the garden |
|---|---|---|---|
| Quick leafy greens | Mizuna, tatsoi, komatsuna, mustard greens | Early spring, then late summer into fall | The backbone: baby leaves in weeks, cut again as they regrow |
| Bok choy and choy sum | Baby bok choy, full-size bok choy, choy sum | Spring for baby size, fall for full heads | Reliable if harvested before heat or hard freeze |
| Heading types | Napa cabbage | Fall only | Needs a long stretch of cooling weather to form heads |
| Heat lovers | Amaranth, water spinach | Summer, once soil is truly warm | Optional, best in the southeast and sunny, sheltered sites |
The full growing basics are in Growing Asian Greens in Pennsylvania.
What will not work here
Spring napa cabbage tops the list of failures. Heads take roughly two to two and a half months from sowing, so an April sowing finishes in the long days and warm weather of June. Those are the conditions that make napa send up a flower stalk before it forms a tight head. Napa belongs in the late-summer sowing slot, where the weather is cooling as the heads fill.
Late fall sowing fails for the opposite reason. The first fall freeze lands between November 5 and November 16 at the reference station, and earlier in the north and at elevation. Growth also slows sharply as October days shorten, well before any freeze. Full-size bok choy sown in mid-October will not size up. Baby leaves and cut-and-come-again mizuna still have a chance. Count back from your first expected freeze and add a couple of weeks for the slowdown.
Open-ground winter harvests fail in most of the state. The mean daily minimum of the coldest month at the Philadelphia reference station is 26.0°F. That is the average night in the mildest corner, so colder nights are routine and colder regions fare worse. Bok choy and napa will not make it through unprotected. Tatsoi and mizuna are the hardiest of the group and can sit through winter under a low tunnel or cold frame, but expect damaged outer leaves and slow regrowth.
Humid summers defeat close spacing. Thick stands of full-size bok choy or mustard in a muggy July spell stay wet, which invites slugs and fungal leaf spots. Baby-leaf bands sown thickly do fine in cool, drier spring weather. Full heads need elbow room in the damp of fall, and sowing thinner is the cheap fix.
Spring has its own pest. Flea beetles chew tiny holes in young leaves of mizuna, mustard and arugula-type greens, and a lightweight row cover laid at sowing keeps them off. Heat lovers fail in cool pockets. Water spinach and amaranth want warm soil and warm nights, and they stall where the season is short or the nights stay cool.
What changes across Pennsylvania
The USDA Plant Hardiness Zone Map (2023, based on 1991-2020 data) runs from zone 5a to 7b across the state. That is three full zones, so there is no single answer for Pennsylvania. The zone system is built on one variable, the average annual extreme minimum temperature. It tells you what survives winter and says nothing about how many weeks you have before the first freeze or how hot July gets. For dated decisions, use frost dates alongside the zone.
What should a gardener in the northern tier shift?
Push spring sowing later by two to four weeks compared with the Philadelphia dates, and start the fall sowing earlier. Lean on baby leaf and quick types such as mizuna, komatsuna and tatsoi. Give bok choy a spring start under row cover, and plant napa as early in late summer as you reasonably can so it has weeks to head before hard freezes. Skip the heat lovers unless you have a sheltered, sunny wall.
What does altitude change?
The Alleghenies and higher ridges run on the late side in spring and freeze sooner in fall, so the season for tender or slow crops shortens in both directions. Cold air also pools in valleys, so a low spot can freeze while a slope a few feet higher stays clear. On the warm side, the southeast and the Philadelphia area gain a longer fall, which makes late-fall baby greens and winter tatsoi under cover realistic.
To find your own zone, enter your ZIP code in the USDA Plant Hardiness Zone Map. Then pair it with your local frost dates and read When to Sow Asian Greens in Pennsylvania for the sowing windows.
Where to check this for your own county
Start with Penn State Extension, the state’s land-grant extension service. Every county has an office or a connection to one, and the staff know local frost patterns, soil and pests in a way a statewide guide cannot.
Look for two things. The first is a local planting calendar, ideally one that gives spring and fall sowing windows for cool-season vegetables in your county. The second is the varieties trialled near you, meaning which bok choy, mizuna, napa or mustard types actually held up in nearby gardens and research plots. Trial results beat catalog descriptions every time, particularly for bolting resistance in spring and for disease tolerance in damp falls.
Ask about flea beetles, slugs and the usual cabbage-family pests too, since timing for row covers and traps varies by region. Local Master Gardener volunteers often staff help lines and can tell you what has been going wrong lately in your area.
A county recommendation beats a state one. A statewide recommendation has to average across zone 5a mountains and zone 7b suburbs, and nobody gardens in an average. Use the statewide picture to choose types and a rough rhythm, then let your county office correct the dates.
Checking this against your own garden
Your own observations outrank every date in a guide. Three are worth watching, and none needs equipment.
Soil warmth by feel. In the early morning, push your bare hand a couple of inches into the bed. Brassicas germinate in cool soil, so chilly dirt is fine for bok choy and mizuna in spring. For amaranth and water spinach it should feel clearly warm, and if it still feels cold, wait. Beds that warm early are usually sunny, well drained and sheltered, which tells you where to sow first.
The first true leaves. After the seed leaves, the first true leaves show whether the spot suits the crop. Steady, sturdy growth means the bed is warm and bright enough. Slow, pale or leggy seedlings point to cold soil, shade or crowding, and the fix is a different bed or thinner sowing.
Where frost lies at dawn. On the last cold mornings of spring and the first of fall, see where white frost sits on the lawn. Patches that stay frosted longest are your cold pockets. Put hardy mizuna and tatsoi there, and keep bok choy and heading types on the side that clears first.
Jot down the dates you notice each year. Two or three seasons of notes will tell you more about your yard than any statewide calendar.
Common questions
What is the easiest Asian green to grow in Pennsylvania?
Mizuna and komatsuna are the most forgiving. Both grow quickly from direct sowing, tolerate light frost and can be cut young and allowed to regrow. Baby bok choy is a close third if you harvest it before summer heat arrives.
Can I grow bok choy in summer in Pennsylvania?
It is a gamble. Heat and long days push bok choy to bolt, and July humidity brings slugs and leaf spots. Spring and fall plantings are far more dependable, and fall gives the best heads.
Can Asian greens survive Pennsylvania winters?
Tatsoi and mizuna are the hardiest and can overwinter under a low tunnel or cold frame in much of the state. Bok choy and napa will not survive unprotected. The mean daily minimum of the coldest month at the Philadelphia reference station is 26.0°F, and the north and higher ground are colder.
Is napa cabbage worth growing in Pennsylvania?
Yes, as a fall crop. Sow it in late summer so heads fill in cooling weather, and harvest before a hard freeze or cover it. Spring plantings usually bolt in June heat.