Sow at a depth of approx.
0.39 inches (1.0 cm) and aim for a distance of at least
7.8 inches (20.0 cm) between Sweet pea plants. Soil temperature should be kept higher than
10°C / 50°F to ensure good germination.
By our calculations, you should look at sowing Harlow Carr about 42 days before your last frost date.