USDA Zone 12 is frost-free year-round, with average winter lows of 50 to 60°F. There is no last spring frost and no first autumn frost to plan around, so Zone 12 gardeners plant by heat and by the wet and dry seasons instead of by frost dates. The tropical warmth that lets heat lovers grow all year makes 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.
Romaine lettuce is the best lettuce bet for Zone 12. Its upright, crisp leaves tolerate warm weather better than heading types, and a succession of small sowings in the coolest months can keep salads coming for weeks. It still bolts when days get hot, so in the tropics romaine is a cool-season crop, not a year-round one — plant it when the weather is at its mildest and give it afternoon shade.
Zone 12 at a glance
Zone 12 is frost-free year-round, with average winter lows of 50 to 60°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 12 guidance |
|---|---|
| Average winter low | 50 to 60°F |
| Last spring frost | None — frost-free year-round |
| First autumn frost | None — frost-free year-round |
| Days to germination | 7–10 days |
| Days to maturity | 60–70 days |
| Sowing | both |
| Best planting window | December to February |
| Harvest | 60–70 days after sowing/transplanting |
| Sun | full sun |
| Soil pH | 6.0–7.0 |
| Spacing | 8–12 inches |
| Water needs | moderate |
| Cold tolerance | hardy |
When to plant romaine lettuce in Zone 12
Sow romaine in Zone 12 during the coolest months, roughly December to February, when daytime heat eases and nights are at their coolest. Sow a small batch every two weeks rather than one big sowing, so a bolted batch never leaves you without salad. Seeds germinate in 7–10 days when the soil is cool and moist, and heads are ready in 60–70 days. In the hot, wet months romaine bolts to seed in a matter of weeks and turns bitter, so save your seed for the cool season. Shade cloth or a spot that gets morning sun and afternoon shade buys you a few extra weeks. The planting calendar hub shows the Zone 12 year at a glance, and the December guide covers what else to sow in the coolest month.
Starting romaine lettuce in Zone 12
Romaine can be direct sown or started indoors, and in Zone 12 starting indoors has a real advantage: you can raise seedlings in a cool, shaded spot and transplant sturdy plants out, instead of asking tiny seeds to germinate in warm soil. Sow seed very shallowly — barely covered — in moist seed mix, and keep it evenly damp until it sprouts. Thin or transplant seedlings to 8–12 inches apart once they have a few true leaves. Harden transplants off for a few days in shade before they go into the bed, and water them in well. If you direct sow, sow in the cool of the evening and keep the row shaded and moist with a light mulch or a board lifted once seedlings appear.
Soil, spacing, sun and water
Romaine Lettuce grows best in full sun, in soil with a pH of 6.0–7.0, spaced 8–12 inches apart. Dig in compost before planting and mulch lightly to hold moisture. Give plants room so air moves between them — in Zone 12 humidity, airflow is the best defence against leaf diseases. This crop has moderate water needs: 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. Keep the bed weed-free, and feed lightly with compost rather than heavy fertiliser, which pushes soft, disease-prone growth. The seed-spacing calculator can work out quantities for your bed.
Companion planting
Good companions for romaine lettuce 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 (Asteraceae) grew last year. A related crop to plan alongside is iceberg lettuce, which shares the Zone 12 calendar, so the two guides work well together.
Pests and problems
The common pests and problems to watch for with romaine lettuce are aphids, slugs, thrips. 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. Fungal problems are the bigger worry in Zone 12 humidity: water at the base, space widely, and mulch to stop soil splashing onto leaves. If you are unsure what you are looking at, the pest identifier helper can narrow it down.
Harvest and storage
Pick romaine as a whole head when the leaves are full and crisp, about 60–70 days after sowing, or harvest it cut-and-come-again by taking the outer leaves first and letting the centre keep growing. Outer-leaf picking stretches the harvest and is the best approach in Zone 12, because a head left too long in warming weather bolts. Harvest in the cool of the morning, when leaves are crispest, and use the leaves the same day — romaine wilts fast in tropical heat. Once a plant sends up a tall central stalk and the leaves taste bitter, it is done; pull it and sow the next batch. Romaine does not store well, so succession sowing beats a big single harvest.
Frequently asked questions
When should I plant romaine lettuce in Zone 12?
In the coolest months, roughly December to February. Zone 12 is frost-free year-round with winter lows of 50 to 60°F, so plant by heat, not frost. Check your local extension service for your area.
How long does romaine lettuce take to grow in Zone 12?
Seeds germinate in 7–10 days and heads are ready in 60–70 days. Sow a small batch every two weeks in the cool season for a steady supply.
Why did my romaine bolt so fast?
Heat. Romaine bolts and turns bitter as soon as days warm up, which is why it is a coolest-months-only crop in Zone 12. Afternoon shade and steady water slow it down but cannot stop it.
Can I grow romaine in a container in Zone 12?
Yes — a pot in morning sun and afternoon shade works well, and you can move it to the coolest spot you have. Keep the mix evenly moist and pick outer leaves often.