Try to aim for a seed spacing of at least
11.7 inches (30.0 cm) and sow at a depth of around
0.12 inches (0.32 cm). Soil temperature should be kept higher than
7°C / 45°F to ensure good germination.
By our calculations, you should look at sowing Thumble's Variety about 56 days before your last frost date.
As Thumble's Variety is hardy, ensure temperatures are mild enough to plant out - wait until after your last frost date to be on the safe side.