Radishes are the fastest crop you can grow in Zone 12, and the most forgiving way to learn the cool-season window: with winter lows of 50 to 60°F, they grow best in the coolest months, roughly December through February, and they are ready in just 25–40 days. They are also the quickest to tell you when it is too hot — sow them in the coolest months, pick them promptly, and they are crisp, mild and sweet.
The Zone 12 challenge is heat. These are cool-season crops, and in a frost-free tropical zone the coolest months are short — plant by the coolest part of the year, give afternoon shade, and accept that the season is brief and the harvest smaller than in a cool climate.
Zone 12 at a glance
USDA Zone 12 covers the warmest lowland parts of Hawaii and Puerto Rico. Winters are very mild, with average winter lows of 50 to 60°F, frost is unknown, and the growing season runs all year. Zone 12 has no average last spring frost and no average first autumn frost — it is frost-free year-round — so planting dates here are averages and guidance, not exact dates for any one garden; check your local extension service before planting.
| Detail | Zone 12 guidance |
|---|---|
| Average winter low | 50 to 60°F |
| Average last spring frost | frost-free (no frost dates) |
| Average first autumn frost | frost-free (no frost dates) |
| Days to germination | 4–7 days |
| Days to maturity | 25–40 days |
| Sowing | direct sow |
| Sun | full sun |
| Soil pH | 6.0–7.0 |
| Spacing | 2–3 inches |
| Water needs | moderate |
| Cold tolerance | hardy |
When to plant radishes in Zone 12
Plant radishes in Zone 12 in the coolest months only, roughly December through February. Seeds germinate in 4–7 days and the crop matures in 25–40 days, so a sowing made in December is ready around January to January. Zone 12 is frost-free, so there are no last or first frost dates — check your local extension service for advice on your own microclimate. Sown outside the cool window, this crop bolts, turns bitter or fails to size up in the heat, so treat the coolest months as the whole season and plan other crops for the hot months.
The planting calendar hub and the December in Zone 12 month guide show what else is happening at planting time.
Starting radishes in Zone 12
Sow radishes direct where they are to grow — they germinate in 4–7 days, the fastest of any common vegetable, and they dislike transplanting. Sow little and often, a short row every week or two through the cool season, spacing seed 2–3 inches apart, and keep the seed bed damp until seedlings appear.
See also when to plant radishes in Zone 11 for the same crop in a slightly cooler zone.
Soil, spacing, sun and water
Radishes need full sun and loose, well-drained soil with a pH of 6.0–7.0. Dig the bed over and work in a little well-rotted compost, space plants 2–3 inches apart, and keep the soil evenly moist — radishes that dry out turn hot and woody. They need full sun and a soil pH of 6.0–7.0. Water needs are moderate: water deeply and regularly at the base, in the morning, so leaves dry before night. The germination time calculator can help you plan the bed before you plant.
Companion planting
Marigolds, basil, onions and lettuce are good companions for radishes. Lettuce is the classic partner — radishes mark the row and are harvested before the lettuce needs the space — and onions fill the bed without competing for the same root depth. The companion planting finder can suggest combinations for your whole bed, and our guide to when to plant turnips in Zone 12 shows another crop that shares the same planting windows.
Pests and problems
The common pests and problems to watch for with radishes are cabbage worms, aphids, flea beetles, slugs. Cabbage worms are green caterpillars that chew holes in leaves; check leaf undersides and hand-pick, or cover with fine mesh. Aphids cluster on soft new growth and leaf undersides; wash them off with a strong jet of water and encourage ladybirds. Flea beetles chew small holes in leaves, worst on young seedlings; fine mesh row cover and mulching help. Slugs feed at night, leaving ragged holes and slime trails; water in the morning and keep the bed clear of debris. Your local extension service can confirm an identification if the damage is severe.
Harvest and storage
Pull radishes as soon as they are full-sized for their variety — check by brushing soil away from the shoulder. Radishes left in the ground go woody and hot within days in Zone 12, so harvest promptly and sow again rather than waiting. Fresh radishes keep for about a week in the fridge in a bag, with the tops removed. Eat them fresh — radishes do not store or freeze well, which is why little-and-often sowing matters.
Frequently asked questions
When should I plant radishes in Zone 12?
Plant radishes in Zone 12 in the coolest months only, roughly December through February. Zone 12 is frost-free year-round, so there are no last or first frost dates — plant by the heat and the wet and dry seasons, and check your local extension service for your own microclimate.
Why are my radishes all tops and no root?
Heat, crowding and dry soil are the usual causes: radishes sown outside the coolest months put their energy into leaves, and plants spaced too closely never swell. Sow in the coolest months, thin to 2–3 inches apart, and keep the soil moist.
Can I grow radishes in Zone 12 year-round?
No — not well. This is a cool-season crop, and outside the coolest months, roughly December through February, it bolts, turns bitter or fails to size up in tropical heat. Grow it in the cool window, and plant heat-loving crops in the hot months instead.
Why are my radishes so hot?
Heat and age make radishes hot: roots left in warm soil, or left in the ground too long, turn sharp and woody. Pick radishes young, keep the soil moist, and grow them only in the coolest months for the mildest flavour.