DO NOT SOAK SEEDS
Start seeds 6-8 weeks before your last frost. If you dont know this date you can look it up here: https://www.almanac.com/gardening/frostdates
If you dont know your growing zone look it up here: https://www.almanac.com/what-are-plant-hardiness-zones
Sweet pea seeds love extra room to develop deep roots. They also like to grow slow and cold. In some zones (7 and above) seeds can be started in the fall and overwintered. Some seeds like tomatoes like a warm environment to grow, sweet peas on the other hand like a cool 50-55' F to develop a healthy root structure before getting planted out.
If your just growing a few plants a standard 4" nursery pot is just fine. If you keep temps cool your sweet pea will grow nice and slow. If in a heated space it will shoot up too tall and too fast focusing on foliage growth instead of roots. Once the weather warms the plants are ready to get transplanted out into the garden. Make sure they have something to grow up, tendrils will reach for something to grab onto and will need some help getting established. Some twine to corral or wrap around when they are young.
Pinch when plants have 4 sets of true leaves or roughly 6-8" tall. This will encourage side branching or the plant will send up new shoots close to the base. This will encourage a fuller plant.
Plant or thin to approx 6-8"
Plant seeds 1/2 to 1" deep.
If starting seeds outside you follow the same rules as above but just note that voles and mice love to eat fresh sweet pea seeds and will dig them up to eat. You can cover them until sprouts emerge and then keep an eye out for slugs when they are young.
