When to plant onions zone 13 — in USDA Zone 13, that question has a different answer from almost anywhere else in the United States. Zone 13 is the hottest USDA zone, frost-free year-round with average winter lows above 60°F, so there is no last frost to wait for and no first frost to beat. Instead you plant by heat and by the wet and dry seasons, and onions is a cool-season crop, and in Zone 13 it is a coolest-months-only crop. This guide gives the timing and the honest limits, using published crop ranges — and, as always, check your local extension service for varieties suited to your area.
When to plant onions in Zone 13
Onions are a cool-season crop in Zone 13, and the variety you choose matters more than the exact sowing date. Tropical onions must be short-day types — varieties that bulb up when days are short, around 10–12 hours — because long-day varieties bred for northern summers will never bulb properly near the equator. Sow or plant in the coolest months, roughly December through February, so bulbs form and mature before the heat and humidity of the hot season bring disease.
Zone 13 covers only the hottest tropical parts of the United States, so these are zone averages, not a promise for any single garden — microclimate, elevation, rainfall and soil all shift the details.
Zone 13 planting data for onions
Published ranges from standard horticultural references — germination and maturity vary by variety, soil and weather, so treat them as guides, not guarantees. Zone 13 is frost-free, with average winter lows above 60°F, so no frost dates appear here: there are none to give.
| Detail | Onions in Zone 13 |
|---|---|
| Germination | 7–14 days |
| Days to maturity | 90–120 days |
| Spacing | 4–6 inches |
| Soil pH | 6.0–7.0 |
| Sun | full sun |
| Sowing method | both |
| Cold tolerance | hardy |
| Water needs | moderate |
| Family | Amaryllidaceae |
For the wider year, see the planting calendar hub and the cool-season month guides such as January in Zone 13.
Starting onions in Zone 13
Start onions from seed indoors, or plant sets and seedlings in the cool season — either method works, and germination takes 7–14 days. Seed gives the widest choice of short-day varieties, but sets are quicker and simpler. Plant seedlings or sets shallowly, with the tip just showing, and do not bury them deep: deep planting makes thick necks and poor bulbs. Keep the bed weed-free while plants are young, because onions compete badly with weeds.
Soil, spacing and sun for onions
Onions want full sun and well-drained, fertile soil with a pH of 6.0–7.0. Dig in compost before planting, and keep the soil loose so bulbs can swell. Space plants 4–6 inches apart, and mulch lightly to hold moisture without burying the bulbs — onions bulb best when the top of the bulb sits near the surface and gets some sun. Avoid fresh manure, which encourages thick necks and soft bulbs that do not store.
Watering onions in Zone 13
Onions have moderate water needs, with steady moisture most important while bulbs are swelling. Drought at that stage gives small bulbs, while watering late in the season — once tops start to fall over — makes bulbs soft and poor keepers. Water at the base in the morning, and stop watering once the tops begin to yellow and fall. In the wet season, raised beds help, because onions rot quickly in waterlogged soil.
Companion planting for onions
Good companions for onions include marigolds, basil, onions and lettuce. These pairings come from standard companion-planting references. Keep companions low and open so air can move, and avoid planting onions next to other members of the Amaryllidaceae family in the same season, since they share pests and diseases. For a quick check, try the companion planting finder.
Pests and problems in Zone 13
The common pests for onions are aphids, slugs and cutworms. In Zone 13, warm, humid weather means pests and diseases are active all year — there is no winter to knock them back — so check plants every few days and act early. A strong jet of water knocks most aphids off, hand-pick larger pests in the morning, and remove badly infested leaves before a small problem becomes a large one. If damage is severe or you cannot identify the culprit, ask your local extension service — and use the pest identifier helper to narrow it down.
Harvest and storage
Onions take 90–120 days to maturity, so a cool-season planting is ready as the hot season arrives. Harvest when the tops yellow and fall over naturally — do not bend them over yourself. Pull bulbs on a dry day, lay them in the sun or under cover for a few days to cure, and store in a cool, dry, airy place. Well-cured onions keep for weeks; soft or thick-necked bulbs should be used first. In tropical humidity, curing under cover with good airflow matters more than sun.
Related reading
- Garlic in Zone 13 — another crop from this Zone 13 batch, with the same frost-free timing.
- Onions in Zone 11 — the same crop in a cooler zone, for comparison.
Frequently asked questions
Can you grow onions in Zone 13?
Yes, in the coolest months, roughly December through February, but only short-day varieties. Zone 13 is frost-free with winter lows above 60°F, and day length near the tropics is short, so long-day varieties will not bulb. Check your local extension service for short-day varieties suited to your area.
Why didn't my onions form bulbs?
Wrong variety is the usual cause — long-day onions will not bulb in the tropics. Deep planting and heavy feeding also give thick necks instead of bulbs. Plant shallowly, choose short-day types, and keep feeding modest.
When should I stop watering onions?
Once the tops start to yellow and fall over. Watering after that makes soft bulbs that rot in store. Onions take 90–120 days to maturity, so plan the last watering a couple of weeks before harvest.
How do I store onions in the tropics?
Cure them first: lay bulbs under cover with good airflow for several days until necks are dry and papery, then store in a cool, dry, airy place. Use soft or thick-necked bulbs first.