Aim to sow
0.5 inches (1.27 cm) deep and try to ensure a gap of at least
1.88 feet (58.0 cm). Soil temperature should be kept higher than
21°C / 70°F to ensure good germination.
By our calculations, you should look at sowing Hero of Lockinge about 14 days before your last frost date.
As Hero of Lockinge is hardy, ensure temperatures are mild enough to plant out - wait until after your last frost date to be on the safe side.