Sow
0.49 inches (1.25 cm) deep with a guideline distance of
3.12 inches (8.0 cm). Soil temperature should be kept higher than
8°C / 46°F to ensure good germination.
By our calculations, you should look at sowing Sardinia about 60 days before your last frost date.
As Sardinia 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.