Try to aim for a seed spacing of at least
2.97 inches (7.62 cm) and sow at a depth of around
0.99 inches (2.54 cm). Soil temperature should be kept higher than
4°C / 39°F to ensure good germination.
By our calculations, you should look at sowing Progress #9 about 35 days before your last frost date.
As Progress #9 is half hardy, ensure temperatures are mild enough to plant out - wait until after your last frost date to be on the safe side.
Laxton’s Progress # 9, Progress 9