Look to ensure a distance
3.12 inches (8.0 cm) between seeds when sowing - bury at a depth of at least
0.49 inches (1.25 cm) deep. Soil temperature should be kept higher than
8°C / 46°F to ensure good germination.
By our calculations, you should look at sowing Summer green about 60 days before your last frost date.
Ensure that temperatures are mild (minimum night temperatures should be around 0°C / 32°F) and all chance of frost has passed before planting out, as Summer green is a half hardy plant.