In coastal and southern California, where winter freezes don’t happen, sow Asian greens in the cool half of the year, from fall through winter and into early spring. Stop when the weather turns warm. Heat, not frost, is what ends the season here. In Northern California, the Central Valley and the Sierra, freezes set the calendar instead, and this page has no dated frost figures for them.
The short answer for California
Start with the reference numbers. NOAA’s 1991-2020 Climate Normals for Los Angeles give no computable freeze normal at all (the data carries the code -666, meaning no value could be calculated). Daily records show zero days at or below 32°F in 30 years, and the frost-free season is listed as 365 days. A frost date is normally a probability of a 32°F reading arriving on or after a given date in spring, or on or before it in fall. In this part of California, that probability is so low that no date exists to count from.
Where frost does not set the calendar
The coldest month at the same station has a mean daily minimum of 49.1°F. That is the average overnight low in the chilliest month, not a record. For bok choy, mizuna, tatsoi and similar cool-season crops, it describes a mild winter, not a threat. Winter is the productive stretch, and the sowing window runs from fall through early spring. Sowing at intervals through those months gives a steady supply instead of one glut.
The end of the window comes when days warm up and the plants start sending up flower stalks. The earlier you sow in fall, the more of the warm tail you have to survive, so patience in autumn often beats eagerness. For the crops that suit this window, see The Best Asian Greens for California, and for the wider picture of how they grow here, Growing Asian Greens in California.
Where it does freeze
Northern California, the Central Valley and the Sierra do freeze. The Los Angeles figures cannot be carried over to them, and this page does not have a sourced last or first frost date for those regions. Gardeners there should treat the calendar as two windows, one after the last spring freeze and one ending before the first fall freeze, and take the actual dates from a local source (the extension section below explains where).
What will not work here
A 365-day frost-free season is a trap. It suggests you can sow any week of the year, and that is the mistake that ruins the most Asian green plantings in the frost-free parts of the state. A sowing made as the weather warms in late spring runs straight into heat, and leafy brassicas respond by bolting before they make a harvestable head or rosette.
Weekly watering fails too. California’s summers are dry, and a seedbed that gets one deep soak a week dries out between visits. Asian greens are shallow-rooted and fast-growing, so they stall or turn bitter when the top few inches of soil dry out. Frequent light watering, or a drip line on a timer, suits them better than a weekly drench. Many California water districts also set restrictions on irrigation days and hours, so a plan that depends on daily hand-watering may not survive a drought declaration. Check your district’s rules before you plan a summer crop.
Sowing in full summer sun is another loser, even where it never freezes. Seeds of many cool-season greens germinate poorly in hot soil, and what does come up is under stress from day one. Gardeners in the hot inland valleys of Southern California feel this earlier in spring and later in fall than people on the coast.
Then there is the cold side, which is just as specific. In the Central Valley, Northern California and the Sierra, a fall sowing made too late meets a freeze before the plants have size, and seedlings with only their first true leaves have little reserve. Treating Los Angeles as the norm for the whole state would lead a Sierra gardener to sow in a calendar that was never theirs.
A last failure is the assumption that a mild winter means no planning. Coastal gardeners can plant in January, but slow growth in short, cool days means sowings made then mature on a longer timetable than fall ones. Frost-free does not mean fast.
What changes across California
The USDA Plant Hardiness Zone Map 2023, built on 1991-2020 normals, places California in zones 5a through 11a. That is a territory-wide range, not a single answer, and there is no one zone to recommend. It is built on one variable only, the average annual extreme minimum temperature, so it tells you about winter cold and nothing about summer heat or water.
That matters for Asian greens, because heat is half the story in this state. A coastal garden and a high-elevation garden can differ by many zones, and a hot valley may share a zone with a cooler place that has a very different sowing season. Use zones to judge freeze risk, and your own observation to judge heat.
| Area | Freeze in winter? | What sets your sowing window |
|---|---|---|
| Coastal and southern California | None in an average year (Los Angeles reference) | Heat and water: sow fall through early spring |
| Central Valley | Yes | Both freeze and summer heat narrow the windows |
| Northern California | Yes | Freeze dates, plus a cooler spring start |
| Sierra and high elevation | Yes | A short season between freezes |
If you garden in the north or at altitude, shift your sowing later in spring and earlier in fall than any coastal advice suggests, and count backward from your first fall freeze. To see where your own property falls, look it up on the USDA map yourself rather than trusting a regional label.
Where to check this for your own county
California’s state extension service is University of California Agriculture and Natural Resources, and its county offices are the next stop after this page. Look for two things there: the planting calendar written for your county, and any vegetable varieties trialled in local conditions. A trial in your county tells you which Asian greens held up through your heat and your water, which no state-level page can.
Many counties also run Master Gardener programs through the same system, and their local guides tend to give sowing windows by month for a specific valley, coast or foothill. That is the format to look for.
Be clear about what this page is. It gives the state view, and a county recommendation beats a state one every time. A single state spans zones 5a to 11a, so a window that fits the coast could be wrong by weeks for a gardener in the mountains. The frost figures here come from a Los Angeles reference station and describe the frost-free parts of the state. They are a starting point, not the final word for your address.
This page does not have a sourced county-by-county calendar, so it does not offer one. If your county office publishes dates that differ from what you read here, follow your county.
Checking this against your own garden
Your own observations outrank every date above. Three are worth watching, and none needs equipment.
- Soil warmth by feel. Push your hand into the bed in the morning. If the soil feels cool and damp, cool-season seed will germinate well. If it feels warm even early in the day, that spot is already past the window. Compare a shaded bed with a sunny one and you have mapped your microclimate.
- The first male flowers on squash. When they open, warm weather has settled in, and it is time to stop sowing cool-season greens until fall. If they appear earlier in your yard than a neighbor’s, your garden runs warm.
- The first true leaves. Seedlings that grow quickly with sturdy leaves are comfortable. Tall, thin ones are stretching for light or reacting to heat, and a pale, slow start points to cold or wet soil.
Write down the date of each observation for one year and you will have a calendar that fits your lot better than any page can.
Common questions
Can I sow Asian greens year-round in Los Angeles?
Frost will not stop you, since Los Angeles records show no freeze in 30 years. Summer heat will, though. Plan on fall through early spring for most greens.
When is the last frost in California?
It depends on where you are. Coastal and southern California has none in an average year, while Northern California, the Central Valley and the Sierra do freeze. This page has no dated frost for those regions.
Is my hardiness zone enough to plan my sowing?
No. California spans USDA zones 5a to 11a, and a zone reflects only the average annual extreme minimum temperature. It says nothing about heat or watering, which matter just as much for greens.
Where do I find a calendar for my county?
Go to your county office within University of California Agriculture and Natural Resources, and ask for the local planting calendar and any varieties trialled nearby. Many county offices also list Master Gardener contacts who can answer variety questions.