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.
Red onions are the sweet, colourful onion for salads, salsas and grilling, with a milder bite than yellow storage onions. In Zone 11 they are a cool-season crop: they take 90–120 days to mature, which is a long time in a short cool season, so they need to be planted at the very start of the cool window. Choose short-day varieties, which are bred for southern latitudes where day length changes little through the year.
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 |
| 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 red onions in Zone 11
Plant red onions from November through February, in the coolest months, from sets, transplants or seed. Because the crop takes 90–120 days to mature, a November planting is ready roughly in February or March, while a late planting will still be bulbing when the heat arrives and may never size up properly. Seeds germinate in 7–14 days. Short-day varieties are the right choice for Zone 11's latitude — long-day types bred for northern summers will not bulb properly this far south.
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 red onions in Zone 11
Red onions can be started from seed indoors, from transplants, or from sets, and in Zone 11 sets and transplants are the most reliable: they give you a head start on the long season. If you start from seed, sow indoors in trays, keep the mix moist, and transplant thin, pencil-sized seedlings out when they are sturdy. If you use sets, plant them pointed end up, just barely covered, and firm the soil around them. Harden off indoor-started plants for a few days before they go out.
Soil, spacing, sun and water
Red Onions grows best in full sun, in soil with a pH of 6.0–7.0, spaced 4–6 inches apart. Red onions want loose, fertile, well-drained soil and steady moisture while they are bulbing. Dig in compost and work the bed deeply so bulbs can swell without hitting compacted soil. Water evenly — drought while bulbs are sizing up gives small, pungent onions — and stop watering as the tops begin to fall over, so bulbs can cure. Red 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 red 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 yellow 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 red onions are aphids, slugs, cutworms. Aphids cluster on leaves and can be washed off with water. Slugs chew young leaves at night in humid weather — check in the evening and keep mulch back from the necks. Cutworms can sever young seedlings at soil level, so protect new plantings with a cardboard collar. In Zone 11's warmth, onion rot is a risk in wet soil, so use raised beds and never let the bed stay soggy. 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 red onions when the tops yellow and fall over on their own — that is the plant telling you the bulb is finished. Lift them gently with a fork on a dry day, leave them to cure in the sun or in a dry, airy spot for a week or two until the necks are papery, then trim the tops and store in a cool, dry, dark place. Red onions are milder and sweeter than yellow onions but do not store as long, so use them first and eat them fresh where you can.
Frequently asked questions
When should I plant red onions in Zone 11?
Plant from November through February, in the coolest months. Zone 11 is frost-free year-round, so the window is set by heat — and onions need 90–120 mild days. Check your local extension service for your area.
How long do red 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 on that long season.
Why didn't my onions form bulbs in Zone 11?
Usually the wrong day-length type: long-day varieties bred for northern summers will not bulb this far south. Grow short-day varieties, and plant early in the cool season.
What soil and spacing do red 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 raised beds where rain is heavy.