Growing onions in USDA Zone 11 means frost-free and tropical: plant by heat and the wet/dry season, not by frost dates. Onions are a cool-season crop that can be grown in Zone 11, but only in the coolest months and only with short-day varieties, which are the types that bulb up when days are short. Long-day varieties grown here will stay green and never form a bulb. This guide covers when to plant onions in Zone 11, with the soil, spacing, sun, water and care it needs. Use the Zone 11 planting calendar to see what else to sow alongside it.
Zone 11 at a glance
USDA Zone 11 has average winter lows of 40 to 50°F and is frost-free year-round — there is no last or first frost date to plan around. Plan by heat and by the wet and dry seasons instead: heat lovers grow year-round, while cool-season crops only succeed in the coolest months. These are zone averages, not promises for any one garden, so check your local extension service for your area.
| Detail | Zone 11 guidance |
|---|---|
| Last / first frost | None — Zone 11 is frost-free year-round |
| Average winter low | 40 to 50°F |
| Days to germination | 7–14 days |
| Days to maturity | 90–120 days |
| Sowing | Direct sow, or start indoors and transplant |
| Transplanting / planting out | Year-round (frost-free); best results in the planting window above |
| Harvest | Harvest 90–120 days after sowing/transplanting; pick regularly |
| Sun | full sun |
| Soil pH | 6.0–7.0 |
| Spacing | 4–6 inches |
| Water needs | moderate |
When to plant onions in Zone 11
In Zone 11, plant onions in the coolest months, roughly December to February, so bulbs form while days are short and temperatures are at their lowest. Zone 11 is frost-free, with average winter lows of 40 to 50°F, so there is no frost to work around — heat and day length are the limits instead. Onions take 90–120 days to maturity. Check your local extension service for short-day varieties that suit your area. If you are unsure of your own dates, the seed-starting calculator will help you work the timing out. Frost dates are zone averages — check your local extension service before you commit to a date.
Starting onions in Zone 11
Onions can be started indoors from seed or planted as sets, and sets are the easier route in Zone 11. Sow seed indoors and transplant sturdy seedlings, or push sets into the soil so just the tip shows. Seeds germinate in 7–14 days. Space plants 4–6 inches apart in rows, and keep the bed weed-free, since onions compete badly with weeds.
Soil, spacing, sun and water
Onions want full sun and rich, well-drained soil with a pH of 6.0–7.0. Dig in compost before planting and keep the bed loose, since bulbs cannot swell in compacted ground. Mulch lightly to hold moisture, but keep mulch away from the necks of the bulbs. Onions need moderate water. Water at the base in the morning, keep the soil moist while bulbs are swelling, and stop watering as the tops begin to fall over and the bulbs ripen — wet soil at that stage causes rot in storage.
Companion planting
Good companions for onions include marigolds, basil, onions, lettuce. The companion planting finder can suggest combinations for your whole bed. Do not plant onions where other alliums grew last year, and do not let weeds take over the bed. Good companions include marigolds, basil and lettuce around the edges, and onions themselves are good companions for many crops.
Pests and problems
The common pests and problems to watch for with onions are aphids, slugs, cutworms. Aphids cluster on leaves, slugs take young plants, and cutworms can sever stems at soil level. Inspect plants when you water, wash aphids off, and keep the bed clear of debris. Good drainage and spacing matter more than anything else in humid weather.
Harvest and storage
Onions are ready 90–120 days after planting. Harvest when the tops fall over and begin to yellow, then lift the bulbs and let them cure in the sun or in a warm, airy place for a week or two until the skins are papery and the necks are dry. Store cured onions in a cool, dry, airy place in a net bag or braided, and use within a few months. Do not store soft or damaged bulbs, and keep onions away from potatoes, which make each other spoil faster.
Making the most of Zone 11
Zone 11 onions depend on two things: short-day varieties and a cool-season planting. Get those right, keep the bed weed-free, and stop watering as bulbs ripen, and you will have onions that keep for months. Related reading: Garlic in Zone 11 and December in Zone 11. For how the same crop behaves one zone colder, see Onions in Zone 9.
Frequently asked questions
When should I plant onions in Zone 11?
In Zone 11, plant onions in the coolest months, roughly December to February, so bulbs form while days are short and temperatures are at their lowest. Check your local extension service — these are zone averages, not exact dates for your garden.
How long do onions take to grow in Zone 11?
Seeds germinate in 7–14 days, and the crop takes 90–120 days to maturity. In Zone 11, allow the longer end of the range if conditions are cool or dry at sowing time.
Which onions grow best in Zone 11?
Short-day varieties grow best in Zone 11, because they form bulbs when days are short, while long-day varieties stay green and never bulb up in low latitudes, so check the variety description before you buy.
What soil and spacing do onions need in Zone 11?
Onions need full sun and soil pH 6.0–7.0, spaced 4–6 inches apart. Dig in well-rotted compost, water deeply, mulch, and test your soil through your local extension service.