Sow at a depth of approx.
0.23 inches (0.6 cm) and aim for a distance of at least
0.98 inches (2.5 cm) between Cornflower plants.
By our calculations, you should look at sowing Blue Boy about 7 days after your last frost date.
Ensure that temperatures are mild (minimum night temperatures should be around 16°C / 61°F) and all chance of frost has passed before planting out, as Blue Boy is a half hardy plant.