Sow Asian greens in Oregon in two windows: late winter through April, and late July through early September. Spring sowings have to finish before the long days of early summer push the plants to flower. Fall sowings ride into the mild, wet winters west of the Cascades. The dates below are built on Portland, and they do not carry over to the high desert.
The short answer for Oregon
Around Portland, sow Asian greens outdoors from late February through April, then again from late July through early September. Hardy types such as mizuna, tatsoi and mustards can go in a little later in fall and stand through winter under row cover.
Both windows hang on frost dates. The NOAA 1991-2020 climate normals for the Portland reference station put the last spring frost between March 6 and March 21, and the first fall frost between November 11 and November 27. Each range covers the stretch where the chance of a 32°F freeze sits between 30 and 70 percent. A freeze after March 21 or before November 11 still turns up in some years. The full tables are in the NOAA normals file.
Can you sow Asian greens before the last frost?
Yes. Most of these greens germinate in cold soil, and seedlings with a few leaves shrug off a light frost. Seed sown in late February or early March may sit a couple of weeks before it sprouts. A hard freeze can still hurt tiny seedlings, so keep a length of floating row cover handy. A long cold spell also pushes young bok choy and napa cabbage toward flowering, so early sowings do best with bolt-resistant varieties, which are covered in The Best Asian Greens for Oregon.
When do you sow Asian greens for fall in Oregon?
Napa cabbage needs the most time, so it goes in first, in late July or early August. Bok choy, komatsuna and choy sum follow in August. Mizuna, tatsoi and mustard greens mature fast and can be sown into early September. With the first fall frost not due until November 11 to November 27, even the September sowings get weeks of growth before the cold arrives.
Winters west of the Cascades are mild on average. The mean daily minimum of the coldest month at the Portland station is 36.2°F, a few degrees above freezing, so hardy greens often keep producing through winter. Individual nights still drop lower, which is why row cover earns its place. For care after sowing, see Growing Asian Greens in Oregon.
What will not work here
Three plans fail in Oregon season after season: sowing in the heart of summer, watering once a week, and applying Portland’s dates to the high desert. Each one runs into a fixed feature of the climate.
Why do Asian greens bolt in an Oregon summer?
Sowing in May and June for a summer harvest sets up bolting. Days keep lengthening until the solstice around June 20, and warm weather adds to the signal. Bok choy and napa cabbage answer by sending up a flower stalk before the rosette or head has filled out, and the leaves turn bitter. Flea beetles, which thrive in warm, dry weather, riddle the seedlings with tiny holes at the same time.
Weekly watering makes it worse. Summers in western Oregon are mostly dry, and Asian greens root in the top few inches of soil. One long soak leaves that layer dry for days, and the stress hurries plants toward seed. Light watering every couple of days keeps the bed evenly moist.
What fails in fall and winter beds?
Crowding does. Fall rains arrive just as plants reach full size, and tight spacing keeps leaves wet, which invites slugs and rot. Give full-size bok choy about 6 to 8 inches and napa cabbage about a foot. Baby greens can stand a couple of inches apart.
Late sowings of slow crops fail as well. A napa cabbage sown in September will not form a head before short days and cold close in. After mid-August, stick to fast greens.
Do Portland’s dates work in central and eastern Oregon?
No. Central and eastern Oregon are high desert, with a far shorter growing season than the Willamette Valley. Frost comes later in spring and earlier in fall, so the Portland window leaves slow crops without time to finish. Overwintering in an open bed also fails where winter lows run well below Portland’s. In those gardens, pick quick types ready in 30 to 45 days from sowing, and plan on row cover at both ends of the season.
What changes across Oregon
Oregon is many gardens. The USDA Plant Hardiness Zone Map (2023 edition, built on 1991-2020 normals) places the state anywhere from zone 4a to zone 9b. The system rests on one variable, the average annual extreme minimum temperature. It tells you how cold the worst winter nights get and says nothing about summer heat or frost dates. A spread that wide leaves no single answer for the state.
Cold mountain basins and high-desert towns sit at the low end. Mild valley and coastal sites sit toward the warm end. The dates in this article use Portland as the reference, and other parts of the state differ, some by weeks. To learn your own zone, look up your location on the USDA map.
How should you shift sowing dates in northern Oregon or at altitude?
Colder sites squeeze both windows inward. Start spring sowing later, once the soil can be worked and feels cool but not frozen, and use row cover for the first few weeks. Move fall sowing earlier, so plants reach size before hard freezes. As a starting guess, shift each window by a couple of weeks, then adjust from what your own beds do.
The coast goes the other way. Cool summers hold bolting down, so sowing windows stretch longer, though slugs and wet leaves demand more attention. In hotter inland valleys of southern Oregon, summers are drier and the midsummer gap is wider. Shade cloth helps, and fall sowing may need to wait until the heat breaks.
Where to check this for your own county
The best local source is Oregon State University Extension, the land-grant university’s outreach service. Counties have local offices, and many run Master Gardener programs staffed by volunteers who garden in the same soil and weather you do.
A county recommendation beats a state one. The dates above come from a single Portland station and do not apply statewide. A gardener in Hood River, Bend or Medford deals with different frost dates and summer heat.
What should you look for on the extension site?
Four items are worth finding:
- A local planting calendar with spring and fall vegetable sowing dates for your county or nearest town
- Varieties trialled in your county, especially bolt-resistant bok choy and napa cabbage
- Local frost dates and advice on row cover or other season extension
- Pest notes for flea beetles, slugs and cabbage root maggot
If a calendar covers only western or eastern Oregon, pick the side of the Cascades that matches your garden. Then check it against your county office by phone or email.
Checking this against your own garden
Your own observations outrank every date here. Three are worth watching, and none needs a tool.
Start with soil warmth by feel. In early spring, squeeze a handful from the bed. If it crumbles and feels cool rather than icy, it is ready for seed. Soil that clumps into a cold, wet ball needs more time. Comparing a sunny raised bed with a shaded corner shows how much your own spots differ, and the warm bed gets the first sowing.
Next, watch for the first true leaves. The two round seed leaves come up first, and the first true leaves show the plant’s real shape. Note how many days that takes after sowing. A slow arrival in early spring or late fall means a cool bed, and thinning should wait until true leaves appear.
Last, look for the first flower buds, a tight cluster rising from the center of the rosette. Write down the date in your earliest sowing. That date is your cutoff for the next year: sow earlier, or choose a more bolt-resistant variety.
Common questions
Can you grow Asian greens through winter in Oregon?
West of the Cascades, yes, with hardy types such as mizuna, tatsoi, mustards and komatsuna. The mean daily minimum of the coldest month at the Portland station is 36.2°F, so most nights stay near or above freezing. Cover beds during hard freezes. In the high desert, winter lows are much lower and open beds rarely make it.
What is the best month to sow bok choy in Oregon?
Around Portland, August is the safest month for a fall crop, and March or April works for spring. Spring plantings face a higher risk of bolting, so choose a bolt-resistant variety, as outlined in The Best Asian Greens for Oregon.
Do Asian greens need to be started indoors?
No. They grow best sown directly in the garden, and packet days count from sowing. Most are ready in roughly 30 to 60 days, depending on whether you cut baby leaves or let them reach full size.
How late can you sow Asian greens in the high desert?
No fixed date fits every garden there. Count back from your first fall frost using the days to maturity on the packet, and favor fast baby greens in late summer. A county extension office can supply a local frost date. Low spots in a yard often freeze days earlier than the top of a slope.