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.
White onions are the mild, crisp onion for fresh salsas, salads and Mexican cooking, with a clean flavour and none of the harshness of a storage onion. They take the same 90–120 days to mature as other onions, so in Zone 11 they are strictly a cool-season crop, planted at the start of the cool window and eaten fresh rather than stored for months.
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 white onions in Zone 11
Plant white onions from November through February, in the coolest months, from sets, transplants or seed. With 90–120 days to maturity, a November planting is ready roughly in February or March, while a late planting will still be bulbing when the heat arrives. Seeds germinate in 7–14 days. Choose short-day varieties bred for southern latitudes — long-day types will not bulb properly in Zone 11's short winter days.
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 white onions in Zone 11
White onions can be started from seed indoors, from transplants, or from sets; sets and transplants are the most reliable in Zone 11 because they shorten the long season. Start seed indoors in trays, keep the mix moist, and transplant thin seedlings out when sturdy. Plant sets pointed end up, just barely covered, and firm the soil around them. Harden off indoor-started plants for a few days first, and water transplants in well.
Soil, spacing, sun and water
White Onions grows best in full sun, in soil with a pH of 6.0–7.0, spaced 4–6 inches apart. White onions want loose, fertile, well-drained soil. Dig in compost and work the bed deeply so bulbs can swell evenly. Keep the bed weed-free — onions have shallow roots and thin leaves, so weeds outcompete them fast. Water evenly while bulbs are sizing up, then stop watering as tops begin to fall over, so bulbs can cure. White 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 white 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 white onions are aphids, slugs, cutworms. Aphids gather on leaves and wash off with a strong jet of water. Slugs chew young leaves at night in humid weather, so check in the evening and keep mulch back from the necks. Cutworms can cut young seedlings off at soil level; a cardboard collar around new plantings stops them. Wet soil invites onion rot in Zone 11's warmth, so use raised beds and keep the bed draining freely. 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 white onions when the tops yellow and flop over, then lift on a dry day and cure in a dry, airy spot for a week or two until the necks are dry and papery. White onions have thin skins and do not store as long as yellow onions, so plan to use them within weeks rather than months — which suits their role as a fresh-eating onion. Use them raw in salsas and salads, or grill them whole; their mild sweetness is the point.
Frequently asked questions
When should I plant white 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 white onions take to grow in Zone 11?
Seeds germinate in 7–14 days and bulbs take 90–120 days to mature. Sets and transplants shorten that long season.
Do white onions store well in Zone 11?
Not as well as yellow onions — they have thin skins and are best used within weeks of harvest. Grow them as a fresh-eating onion and cure them well before storing.
What soil and spacing do white 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 bed.