Sow at a depth of approx.
0.98 inches (2.5 cm) and aim for a distance of at least
1.95 inches (5.0 cm) between Onion plants. Soil temperature should be kept higher than
13°C / 55°F to ensure good germination.
By our calculations, you should look at sowing red odourless about 28 days before your last frost date.
As red odourless is very hardy, ensure temperatures are mild enough to plant out - wait until after your last frost date to be on the safe side.