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 corrado about 28 days before your last frost date.
Ensure that temperatures are mild and all chance of frost has passed before planting out, as corrado is a very hardy plant.