Western Oregon gives Asian greens two openings. One is a spring sowing as soon as the ground can be worked. The other is a late-summer sowing that runs through fall and often into winter, and it is the stronger of the two. At Portland, the last spring freeze falls between March 6 and March 21, and the first fall freeze between November 11 and November 27. Central and eastern Oregon run on a much shorter calendar.
When the soil is warm enough in Oregon
Around Portland, the last spring freeze lands between March 6 and March 21. That window comes from the 30 to 70 percent band of 32°F freeze probabilities in NOAA’s 1991-2020 U.S. Climate Normals. Any given year can fall outside it, so treat the dates as a planning range. Portland sits west of the Cascades. Central and eastern Oregon are high desert with a far shorter season, so don’t apply this window statewide.
A frost date tells you when freezing air stops arriving. It says little about the ground, which warms later. Soil holds the cold of winter longer than air does, and in western Oregon it also holds water. March beds are often cold and saturated at the same time.
How do you tell the soil is ready for Asian greens?
Asian greens are cool-season brassicas, so they do not need summer-warm ground to germinate. What they need is soil that is workable and not waterlogged. Grab a handful from a few inches down. If it forms a muddy ball that stays stuck together when you poke it, wait. If it crumbles, you can sow. A soil thermometer pushed in at seed depth first thing in the morning gives a better read than the air temperature. Seed that sits in cold, soggy ground tends to rot before it sprouts, and what does come up grows slowly and invites slugs.
Early matters for a second reason. Spring sowings run straight into lengthening days, and most of these greens respond to long days and warm spells by bolting, sending up a flower stalk and turning bitter. A March or early April sowing of fast leafy types such as bok choy, tatsoi, mizuna and komatsuna can be cut young, before the weather turns. A sowing that waits until May is gambling against bolting. The Growing Asian Greens: Fast, Cold-Hardy, and Prone to Bolting guide explains how day length and heat trigger that switch.
Gardeners east of the Cascades face a different spring. Nights stay frosty well past the Portland dates, and elevation moves everything later. Neighbors across the Idaho line deal with a similar pattern, covered in Growing Asian Greens in Idaho. For the best local start date, check with the Oregon State University Extension office that serves your county, since the right day varies with elevation and exposure.
How long the season lasts here
Between the mean last spring freeze (March 6 to March 21) and the mean first fall freeze (November 11 to November 27), the Portland reference station has a long frost-free season.
That is a long window, and brassicas that mature in cool weather fit into it twice. A first sowing goes in during March and April and is harvested before summer heat arrives. A second sowing goes in from midsummer into early fall and matures as the days shorten and the nights cool. Where the window is long, as it is west of the Cascades, a missed sowing is an annoyance rather than a lost year.
Can you sow Asian greens more than once in western Oregon?
Yes, and the fall sowing is the one to plan around. Work backward from the November 11 to 27 range. Take the days-to-maturity number on the seed packet, which counts from sowing for direct-seeded greens and roots, then add a generous cushion, because growth slows noticeably as days shorten and light weakens in October. A leafy green that would size up quickly in April crawls in late October. Sowing early enough that plants are nearly full size by the time fall weather settles in is the safer path.
Within each season, stagger small sowings every couple of weeks instead of planting one large block. A single block of bok choy ripens all at once and then bolts or turns. Staggered rows give a steady cut. The succession sowing guide on this site lays out spacing between sowings and how to match quantities to a household.
Is transplanting worth it in a long season?
West of the Cascades, direct sowing usually does the job, because there is time to resow if a patch fails. Transplants make more sense when the window is tight, such as high-elevation or high-desert gardens, or when a bed is occupied until late in the season. If you buy or raise transplants, check the roots before planting. White, fibrous roots are what you want. Swollen, knobbly or distorted roots point to clubroot, a soil disease that attacks the brassica family, and those plants should be discarded rather than set into your bed.
Heat and water in Oregon
Summers west of the Cascades are dry, with hot spells in July and August. Those spells are a count taken at a reference station, not a description of the whole state. The Willamette Valley, the coast, the Cascade foothills and the high desert all run differently, and the coast stays cool all summer. For a late-summer sowing, the issue is less temperature than moisture. A seedbed in July or August dries out within hours. Water lightly once or twice a day until seedlings emerge, and shade the bed with cloth or a lath frame in the afternoon. Mulch between rows once plants are up. Cool, moist soil around the roots slows bolting more than any other single step.
How cold is too cold for Asian greens in Oregon?
At Portland, the coldest month has a mean daily minimum of 36.2°F (NOAA 1991-2020 Climate Normals). That average sits above freezing, which is why the hardiest greens can stand through a typical western Oregon winter, especially under row cover or a low hoop. But an average hides the cold snaps. A single hard freeze, when nights drop well into the 20s, can end tender types such as bok choy and napa cabbage, while hardier mustards, tatsoi and mizuna often shrug off a light one. Cover plants ahead of a forecast freeze and remove the cover on mild days so moisture does not build up underneath.
Don’t lean on a hardiness zone alone. The USDA Plant Hardiness Zone Map (2023, built on 1991-2020 normals) spans zones 4a to 9b across Oregon, and it is based on a single variable, the average annual extreme minimum temperature. Look up your own zone and compare it with the Portland reference rather than assuming the Portland winter applies to you.
What does a cool, damp spring and fall do to Asian greens?
The long wet shoulder seasons bring their own problems. Slugs feed heavily on young seedlings, so hand-picking at dusk, boards laid as traps and clearing debris along bed edges all help. Downy mildew shows up as yellow patches on the upper leaf with fuzzy gray growth beneath, and it spreads in cool, humid weather. Leaves that stay wet invite rot at the base of bok choy and napa. Spacing plants so air moves through them, watering early in the day and avoiding overhead watering in the evening will head off most of it. Disease pressure builds in the same soil year after year, which makes crop rotation worth the effort here.
Which Asian greens suit Oregon
Choose by type, and let conditions decide. The right match depends on the climate where you garden, which varies a lot across the state.
- Short season (high desert, higher elevations): favor the quickest leafy types, such as tatsoi, mizuna, komatsuna and baby bok choy, which can be cut young and sown again.
- Hot spells in summer: favor types that tolerate heat with airflow and root shade, and shift main sowings to late summer.
- Damp springs and falls (west of the Cascades): put disease resistance first, along with open spacing.
Napa cabbage and larger heading types need the longest, coolest stretch, so they fit the late-summer sowing in western Oregon more than a spring planting. Leafy mustards, including the spicy Asian ones, handle cold well and are the best bet for winter harvests under cover. Chinese broccoli and choy sum do well in cool weather and bolt fast once it warms.
Why not name specific varieties?
Variety names are the part of the advice that depends most on place. A variety that performs in the Willamette Valley can bolt in a week at a drier, hotter site, and the reverse is also true. A list from outside your area can steer you wrong. Oregon State University Extension runs county offices and Master Gardener programs that know which cultivars have held up in local soil and weather. Ask them for current recommendations and which seed sources suit your elevation.
Turnips, rutabagas and daikon-type radishes belong to the same family as mustard greens and bok choy. They share their pests and diseases with cabbage, kale and mustard, so a gardener who rotates turnips into a cabbage bed has not rotated anything. Keep brassicas, Asian greens and roots included, out of a bed for several years after a brassica crop, and see the rotation guide on this site for how to lay out the plan.
Common questions
When should I plant Asian greens near Portland?
Sow in March and April once the soil crumbles in your hand, and again from midsummer into early fall. The mean last spring freeze falls between March 6 and March 21, and the first fall freeze between November 11 and November 27. The fall sowing is usually the better performer, because the cooling days keep plants from bolting.
Do these dates apply to central and eastern Oregon?
No. The dates describe Portland, west of the Cascades. Central and eastern Oregon are high desert with a far shorter season, later spring warmth and earlier fall freezes. Ask your county Oregon State University Extension office for the window that fits your elevation.
Can Asian greens survive an Oregon winter?
The hardiest types often can. Portland’s coldest month has a mean daily minimum of 36.2°F, which is above freezing on average. A hard freeze can still kill tender types like bok choy and napa cabbage, so use row cover or a low hoop when a freeze is forecast and expect tougher leafy mustards and tatsoi to do better.
Can I plant Asian greens where cabbage grew last year?
No. Asian greens, turnips, rutabagas, cabbage, kale and mustard are all brassicas and share pests and diseases such as clubroot and downy mildew. Rotate them to a bed that has been free of brassicas for several years.