When to Plant Radishes in Hawaii
Published: April 24, 2026
Hawaii gardeners in Zone 12a have essentially year-round growing for radish. Cool-season crops like radish are best planted in the cooler winter months (October through February) — summer heat prevents these plants from heading or forming a harvestable crop. This guide gives exact dates for Hawaii based on your local frost calendar.
Radish Planting Dates for Hawaii
| Last frost (average) | Frost-free |
| Transplant outdoors | Year-round (October–March is primary window) |
| Direct sow outdoors | Year-round (October–March is primary window) |
| Expect first harvest | 45–120 days after planting |
| Fall crop start | October |
| Fall harvest | January–March |
| First fall frost (average) | Frost-free |
⚠ Direct sow radishes 4–6 weeks before last frost — one of the fastest crops in the garden. Ready in as little as 22 days. Succession plant every 2 weeks for continuous harvest.
Growing Radishes in Hawaii's Climate
Hawaii's tropical climate gives radish year-round potential, but not all months are equal. Wet season (May through October in most of Hawaii) brings disease pressure that can destroy a radish crop within days if fungal conditions align. Dry season (November through April) is the primary productive window.
Soil drainage matters more in tropical climates than almost anywhere else. Raised beds or heavily amended beds with 50% compost content drain rainfall quickly and keep radish roots oxygenated during heavy storms. Flat beds in native clay soil often fail the first wet season.
Common radish pests to watch for in Hawaii include Flea Beetle and Cabbage Root Maggot. The first line of defense is companion planting: Lettuce and Carrot planted nearby discourage several of these pests by confusing host-plant identification or repelling adults before they can lay eggs. Weekly garden walks in the early morning catch problems when they're still manageable.
Radish Garden Calendar for Hawaii
| Month | Task | Notes |
|---|---|---|
| January | First harvests | Early transplants reach harvest size |
| February | Main harvest month | Peak production month in tropical climate |
| March | Continue harvests | Last window for new plantings before wet season |
| April | Finish harvests | Wet season approaching — harvest ripe crops |
| May ← | Clear beds | Disease pressure rises with wet season; warm-season ornamentals now |
| June | — | |
| July | — | |
| August | — | |
| September | — | |
| October | Prime planting window opens | Direct sow or transplant radish; dry season begins |
| November | Main planting month | Peak planting window for best harvests |
| December | Continue successions | Plant every 2–3 weeks for staggered harvest |
Radish Growing Tips for Hawaii Gardeners
- •Thin to 2-inch spacing when seedlings are an inch tall — crowded radishes produce small woody roots.
- •Succession plant every 10–14 days from early spring through late spring for continuous harvest.
- •Hawaii's tropical climate favors planting radish in dry season (October through April). Wet season plantings are destroyed by fungal disease within weeks.
- •Plant as a row marker for slow-germinating crops like carrots — radishes sprout in days and mark the rows.
Companion Planting for Radishes in Hawaii
In Hawaii's tropical climate, planting radish with Lettuce and Carrot helps deter pests and improve soil. Avoid planting near Hyssop and Grape, which inhibit radish growth through root chemistry or shared pest pressure. See the full radish companion planting guide for the complete list.
Radishes Planting Dates by City in Hawaii
Top cities in Hawaii — select for city-level frost dates and planting calendars.
Frequently Asked Questions
When should I plant radish in Hawaii?
In Hawaii (Zone 12a), direct sow radish around Year-round (October–March is primary window) — 5 weeks before the state's average last frost of Frost-free.
What is the last frost date in Hawaii?
Hawaii's average last frost date is Frost-free in the state's most common Zone 12a. Frost dates vary by city — higher elevations and northern counties run 1 to 3 weeks later than the state average. See the city list below for city-level frost dates.
Can I grow radish year-round in Hawaii?
Yes, Hawaii's frost-free climate supports year-round radish growing. October through March is the primary productive window; summer heat and wet-season fungal pressure limit what you can grow June through September.
What radish varieties grow best in Hawaii?
For Hawaii's Zone 12a, consult a local nursery or extension office for radishes variety recommendations.
When do I start radish seeds indoors in Hawaii?
Radish does not need indoor starting in Hawaii — direct sow around Year-round (October–March is primary window) once soil reaches 40°F. Indoor starting is not recommended for this crop because radish transplants poorly.