USDA Zone 11 is frost-free year-round, with average winter lows of 40 to 50°F. There is no last spring frost and no first autumn frost to plan around, so Zone 11 gardeners plant by heat and by the wet and dry seasons instead of by frost dates. The heat and humidity that let tropical crops grow all year make cool-season crops much harder. Frost dates here are zone averages and vary by microclimate, elevation and year — check your local extension service for guidance for your exact spot.
Yellow onions are the everyday cooking onion: strong-flavoured raw, sweet when cooked, and the best keeper of the onion family, with thick skins that store for months when cured properly. They take 90–120 days to mature, so in Zone 11 they need the full cool season, planted early and harvested before the heat. Of the three onion colours in this batch, yellow is the one to grow if you want onions that last.
Zone 11 at a glance
USDA Zone 11 is frost-free year-round, with average winter lows of 40 to 50°F. Plant by the season: the coolest, driest months for cool-season crops, and the cooler part of the year for the best fruit set on heat lovers.
| Detail | Zone 11 guidance |
|---|---|
| Average winter low | 40 to 50°F |
| Last spring frost | None — frost-free year-round |
| First autumn frost | None — frost-free year-round |
| Days to germination | 7–14 days |
| Days to maturity | 90–120 days |
| Sowing | both |
| Best planting window | November to February (coolest months); short-day varieties suit Zone 11 — the best keeper of the three |
| Harvest | 90–120 days after sowing/transplanting |
| Sun | full sun |
| Soil pH | 6.0–7.0 |
| Spacing | 4–6 inches |
| Water needs | moderate |
| Cold tolerance | hardy |
When to plant yellow onions in Zone 11
Plant yellow onions from November through February, in the coolest months, from sets, transplants or seed. A November planting matures roughly in February or March, after 90–120 days, while a late planting risks running into heat before bulbs have sized up. Seeds germinate in 7–14 days. Grow short-day varieties — they are bred for southern latitudes, and long-day types will not bulb properly in Zone 11.
Work by the season rather than by frost dates: the planting calendar hub gives the Zone 11 picture month by month, and the month guide for November in Zone 11 shows what else is happening at planting time. The harvest date calculator can turn your sowing date into a harvest window.
Starting yellow onions in Zone 11
Yellow onions can be started from seed indoors, from transplants, or from sets, and sets and transplants are the most reliable way to fit the long season into Zone 11's short cool window. Sow seed indoors in trays, keep the mix moist, and transplant thin seedlings out when they are sturdy. Plant sets pointed end up, barely covered, and firm the soil. Harden off indoor-started plants for a few days before moving them out.
Soil, spacing, sun and water
Yellow Onions grows best in full sun, in soil with a pH of 6.0–7.0, spaced 4–6 inches apart. Yellow onions want loose, fertile, well-drained soil. Work the bed deeply and dig in compost so bulbs can swell without meeting compacted soil. Keep the bed weed-free, since onions compete poorly with weeds. Water evenly while bulbs are growing, then stop watering once tops start to fall, so the bulbs dry and cure properly. Yellow Onions needs moderate water: water deeply when the top inch or two of soil feels dry, rather than sprinkling lightly every day, and water at the base in the morning so leaves dry before night. Mulch helps hold moisture.
Companion planting
Good companions for yellow onions include marigolds, basil, onions, lettuce. The companion planting finder can suggest combinations for your whole garden. Rotate crops each year and avoid planting where the same family (Amaryllidaceae) grew last year. A related crop to plan alongside is red onions, which shares the Zone 11 calendar, so the two guides work well together.
Pests and problems
The common pests and problems to watch for with yellow onions are aphids, slugs, cutworms. Aphids cluster on leaves and wash off with water. Slugs chew young leaves at night in humid weather — check in the evening and keep mulch pulled back from the necks. Cutworms can sever young seedlings at soil level, so use cardboard collars on new plantings. In Zone 11's warm, wet soil, onion rot is a real risk, so plant in raised beds and make sure water drains away freely after rain. Inspect plants regularly, especially leaf undersides, and act early: hand-pick larger pests, wash aphids off with water, and remove badly affected leaves. Healthy plants in the right soil and spacing resist pests better than stressed ones. If you are unsure what you are looking at, the pest identifier helper can narrow it down.
Harvest and storage
Harvest yellow onions when the tops yellow and fall over on their own. Lift gently with a fork on a dry day, lay the bulbs out to cure in the sun or a dry, airy spot for one to two weeks until the necks are dry and papery, then trim the tops, brush off loose soil, and store in a cool, dry, dark place in a mesh bag or braid. Properly cured yellow onions are the best keepers of the three colours and can last for months — which is exactly why they are worth the long cool season they demand.
Frequently asked questions
When should I plant yellow onions in Zone 11?
Plant from November through February, in the coolest months. Zone 11 is frost-free year-round, so heat — not frost — sets the window. Check your local extension service for your area.
How long do yellow onions take to grow in Zone 11?
Seeds germinate in 7–14 days and bulbs take 90–120 days to mature. Sets and transplants give you a head start.
Which onion stores longest in Zone 11?
Yellow onions, by a clear margin: thick skins and good curing mean they keep for months in a cool, dry, dark place, while red and white onions are best used within weeks.
What soil and spacing do yellow onions need in Zone 11?
Full sun, loose fertile soil with a pH of 6.0–7.0, spaced 4–6 inches apart, with steady water while bulbing and a weed-free, well-drained bed.