In the low desert around Phoenix, sow Asian greens from fall through late winter and finish before spring heat arrives. Summer is the season to skip. The high country around Flagstaff runs on a different clock, with hard freezes and a calendar built around frost dates like much of the country. Arizona holds both climates, so the right sowing month depends on which one your garden sits in.
The short answer for Arizona
In the low desert, sow Asian greens from about October through February, and leave the hot months alone. Bok choy, mizuna, tatsoi, komatsuna and mustard greens are cool-season crops, and in Phoenix the cool season is the whole winter. Plan around heat, because cold hardly figures in the calendar.
Why is there no frost date to count from?
The usual planting calendar starts with a last spring frost and counts backward. That method has nothing to grip in the low desert. NOAA’s 1991-2020 Climate Normals for Phoenix show no freeze in most years. A rare cold snap can bring 32F between late December and mid January, and the station reached 32F in only 6 of 30 springs. That number is the share of springs in which the thermometer touched freezing at the reference station. It works out to about one spring in five. NOAA lists the frost-free season at 365 days.
Winter nights are cool but gentle. The mean daily minimum of the coldest month is 45.3F at the Phoenix reference station. That is cold enough to slow weeds and pests and warm enough to keep leafy greens growing through December and January. Most Asian greens shrug off a light frost anyway, so a single 32F night is a reason to keep a row cover handy and not a reason to hold off sowing.
How does the sowing window run month by month?
October opens the window, once nights have clearly cooled and the soil is no longer baking. Sow in small batches every couple of weeks and you will have a steady supply instead of one big bolting patch. November through January is the core of the season, when germination is reliable and growth is steady but not rushed. Quick types such as mizuna and baby bok choy suit these months because you can cut them young.
February is the last comfortable month for sowing. Seeds planted then need to be harvested before the warming days of March push the plants to send up flower stalks. After that, each week of delay shortens the harvest and makes the leaves sharper. Treat this range as a working rule for the low desert. Elevation, a south-facing wall or a shaded bed can move your own dates by a few weeks either way.
What will not work here
Summer sowing fails first. Soil in the low desert stays hot well into fall, and brassica seeds sown in it germinate unevenly while the seedlings scorch. Even if a few survive, the plants run to seed before they make a usable leaf. Early fall sowings need afternoon shade and daily light watering until the seedlings are up, and a sowing in the middle of summer is wasted seed.
A weekly watering habit fails next. Asian greens have shallow roots and mostly water-filled leaves. A bed that dries to the bottom between soakings, which is easy to do under dry desert air and strong sun, produces tough, bitter, stunted plants. Seedbeds want the surface kept evenly damp, which in a warm October can mean a light watering every day until the first true leaves show. Once the weather cools, watering can stretch out, but a drip line or a quick morning pass beats a weekly flood.
Waiting for spring is the mistake gardeners from other regions make most often. In much of the country, early spring is the sowing season for leafy greens. In the low desert, a March sowing meets rising temperatures almost at once, and a crop that should have given weeks of harvest bolts in days. The same goes for a copied calendar that says to sow a certain number of weeks before the last frost. With no dependable last frost to count from, the instruction has no starting point.
Large, slow heading types are a gamble too. Full-size napa cabbage and big heading bok choy want a long, cool stretch to fill out. In the low desert that stretch runs from fall into winter, so they have to go in at the front of the window, not the back. A late sowing leaves them half-formed when spring warmth arrives. Loose-leaf types and baby-leaf harvests fit the season better.
At the other end of the state, the failure runs the opposite direction. Sowing outdoors in the high country before the soil thaws and the hardest freezes pass loses seed to cold, wet ground. A cool-season crop there is not at risk from midsummer heat the way it is in Phoenix, but it is exposed to freezes at both ends of the season.
What changes across Arizona
Arizona is not one garden. On the USDA Plant Hardiness Zone Map (2023 edition, built on 1991-2020 normals), the state runs from zone 4b to 10b. That is a spread of six full zones, and no single sowing date fits it. The zone system rests on one variable, the average annual extreme minimum temperature, so it tells you how cold the worst nights get and says nothing about summer heat. Find your own location on the USDA map instead of guessing from the nearest big city.
| Area | Winter cold | Main sowing seasons | What limits the crop |
|---|---|---|---|
| Low desert (reference city: Phoenix) | Rare freezes, a few nights at most | Fall through late winter | Summer heat and early spring warmth |
| Mid elevations | Regular freezes, milder than the high country | Early spring and fall, with some winter sowing under cover | Frost at both ends, plus summer heat in lower areas |
| High country (Flagstaff and similar) | Hard freezes every winter | Spring once soil can be worked, and late summer for a fall crop | Frost dates in spring and fall |
A gardener in the north or at altitude should swap the low desert’s winter calendar for a frost-based one. Sow a spring crop as soon as the soil can be worked, and sow a fall crop in late summer so it matures before the first hard freeze. The summer heat that ruins low-desert crops is less of a problem at elevation, but the growing season is shorter. Pick quick types, and see The Best Asian Greens for Arizona for which ones suit each climate.
Where to check this for your own county
Your state extension service holds the most local answer. University of Arizona Cooperative Extension serves every county through local offices, and its staff know how a valley floor differs from a town a few hundred feet higher. A state-level window gives you the shape of the season. A county recommendation beats it, because county advice reflects local frost records and local soil.
When you open the extension site, look for two things. The first is a vegetable planting calendar for your county or the nearest town of similar elevation. These calendars usually list leafy greens, mustards and cabbage-family crops by month, and they will tell you whether your area follows the low-desert winter pattern or the frost-based pattern of the high country. The second is a list of varieties trialled in your county. A variety that has been grown through a real local season is a better bet than one that sold well in a catalog.
If a calendar lists only generic “greens” or “cool-season vegetables,” look for the entry closest to bok choy, mustard or cabbage and use that. Your county office can also tell you the usual dates of the first and last freezes where you live, which matters if you garden above the low desert. For the broader picture of how these crops fit into an Arizona garden, Growing Asian Greens in Arizona covers soil, water and care from seed to harvest.
Checking this against your own garden
Your own beds will tell you more than any calendar. Three things are worth watching, and none needs equipment.
- Soil warmth by feel. Push your hand a couple of inches into the bed in mid-afternoon. Soil that feels hot, not just warm, will cook seedlings, and a bed in full afternoon sun will stay that way weeks after a shaded bed has cooled. Check again at dawn. A bed that is still noticeably warm in the morning keeps its heat overnight, which is common beside a block wall or on bare gravel, and it tells you to wait a little longer or to shade that spot.
- The first bolting stalk. Watch your earliest sowing for a thickening center and a rising flower stalk. When it appears, your window is closing. Note the date, because it will repeat from year to year and gives you a cutoff more accurate than any state-level range. In a warm pocket it will come early, and in a cooler spot it will come later.
- The first true leaves. Seedlings show their first true leaves, the ones that look like the mature plant, within days to a couple of weeks depending on temperature. If they pop up quickly and stay compact, the bed has the right conditions. Leggy, pale or scorched seedlings point to heat or too little water. Cold-damaged leaf edges after a clear, still night point to a low spot where cold air settles.
Keep a few lines in a notebook each season: sowing date, when the leaves came up, when the first stalk appeared. Two seasons of those notes will outrank any published window for your own yard.
Common questions
Can I grow Asian greens in Phoenix in summer?
Not reliably. Summer heat makes the plants bolt before they produce much, and hot soil hurts seed germination. Start sowing in the fall once nights cool, and use the summer to prepare beds.
Do Asian greens need frost protection in the low desert?
Seldom. Phoenix reached 32F in only 6 of 30 springs, and a freeze, when it comes, falls between late December and mid January. Most Asian greens tolerate light frost, but a row cover on the coldest nights costs little and protects young seedlings.
When should I sow in Flagstaff or other high-country areas?
Use a frost-based calendar. Sow a spring crop as soon as the soil can be worked, and sow again in late summer so the plants mature before the first hard freeze. Your county extension office can give you local frost dates.
Which Asian greens suit the low-desert winter best?
Fast, loose-leaf types such as mizuna, tatsoi, komatsuna and baby bok choy fit the season well, since you can cut them young before spring warmth arrives. Big heading types need to go in early in the window. The variety guide linked above sorts them by climate.