Radishes in the Winter Tunnel for Overwintering & Winter Harvest
From our brassica and root crop product managerRadishes do well in unheated or lightly heated hoophouses for early spring and fall crops, and in mild regions like the South and the West Coast they can grow right through winter.
Protective Structure & Temperature Considerations
Winter radishes in a variety trial.
Unheated or lightly heated high tunnels, or low tunnels, can stretch the radish season.
Don't let the crop sit for long stretches below 30°F (-1°C). Cold-damaged radishes can look normal outside but turn pithy or glassy inside, which spoils them for eating.
Time sowings so the crop is ready before tunnel temperatures fall below freezing. If a cold snap is coming before harvest, add a layer of row cover (AG-19 weight or similar) and take it off when the tunnel warms again. Only use the cover when it freezes.
Row cover (AG-19 or similar) can also help hold the soil at good germination temperatures. Take it off once roots start to form, because leaving it on makes oval or elongated roots more likely.
A lightly heated tunnel removes the risk of freeze damage.
Seeding Dates
In the field, radishes take about 21 days, but in a winter tunnel expect about 5–6 weeks from seed to harvest, because spring and fall bring cooler weather and shorter days.
- For fall sowings, check our planting dates chart for winter harvest to find the best sowing dates for your area based on your Persephone Period (the stretch when days are shorter than 10 hours at your latitude). In our Zone 5b trials, radishes sown in mid-September were ready in about 4 weeks.
- For spring sowings, wait until the tunnel has warmed and the danger of a hard freeze is past. In our Zone 5b trials, radishes sown in mid-March were ready in about 6 weeks.
- Where winters are mild and temperatures seldom drop below freezing, you can grow radishes in the tunnel all winter.
Seeding Rate
- Sow seed 1.5" apart and 0.5" deep.
- Space rows about 3.5" apart.
This spacing makes good use of valuable tunnel space while leaving each radish enough room to size up. Crowded radishes may not form roots at all, or may form long, unsellable ones.
Irrigation
Watering tunnel radishes takes a light touch: give enough for a good crop without overwatering, which splits the roots.
- Week one after sowing: water generously to get a good stand and a strong taproot.
- Weeks 2–4: water only if the soil is quite dry or plants show stress. You want a good taproot to form, and too much water now can crack the roots.
- Final week before harvest: water moderately if needed to finish the crop, keeping the soil moist but not soggy. Too much water can crack the roots.
Variety Selection
We recommend 'Rover' as the most dependable red round radish for overwintering; it did best in both our spring and fall plantings. 'Donato' and 'Pepito' also did well. If you are new to tunnel radishes, try all three to find out which one works best for you.
For other colors, try 'Pearl' (white) and 'Bacchus' (purple). French breakfast types such as 'Nelson' also grow well in winter.
