Try to aim for a seed spacing of at least
3.12 inches (8.0 cm) and sow at a depth of around
0.49 inches (1.25 cm). Soil temperature should be kept higher than
8°C / 46°F to ensure good germination.
By our calculations, you should look at sowing American curled about 60 days before your last frost date.
As American curled is half hardy, ensure temperatures are mild enough to plant out (around 0°C / 32°F as a guideline) - wait until after your last frost date to be on the safe side.