Sow indoors 6-8 weeks before the last average frost date for your area. On the coast this would mean sowing in the first half of February. Or direct sow outdoors in early spring, while the soil is still cool and light frost is still possible. Plants are strongest from an early, indoor sowing. Sweet peas can also be direct sown in the fall wherever winters are mild.
Sow seeds 1cm (½”) deep. If starting indoors, chip seeds or soak them in warm water for 24 hours. Use a seed inoculant for the best results. Maintain a soil temperature of 12-18°C (55-65°F). Seeds should germinate in 10-20 days.
For best results, prepare the sweet pea bed the previous fall. Cultivate the soil to 45cm (18″) deep, incorporating a generous amount of finished compost. Also dig in bone meal. At transplant time, dig ¼ cup complete organic fertilizer into the soil beneath each plant. Space vines at 15cm (6″) and provide trellis support. Mulch around plants to keep the soil as cool as possible, and water during dry weather. Keep plants picked to prolong the blooming period.