Look to ensure a distance
0.98 inches (2.5 cm) between seeds when sowing - bury at a depth of at least
0.23 inches (0.6 cm) deep.
By our calculations, you should look at sowing Blue Diadem about 7 days after your last frost date.
Ensure that temperatures are mild and all chance of frost has passed before planting out, as Blue Diadem is a half hardy plant.