Aim to sow
0.23 inches (0.6 cm) deep and try to ensure a gap of at least
0.39 inches (1.0 cm). Soil temperature should be kept higher than
16°C / 61°F to ensure good germination.
By our calculations, you should look at sowing White about 14 days before your last frost date.
Ensure that temperatures are mild and all chance of frost has passed before planting out, as White is a very hardy plant.