Posted: 12/01/2017 at 15:53
Sweet peas have a long tap root that doesn't like disturbance, you would do better to sow them in root trainers, or toilet roll tubes for cheapness, only one to a pot, you can then plant them out without disturbing the long roots. They don't need heat they are very hardy, can be sown in Autumn, not that I do. You could sow three to a flower pot and plant the whole lot out together.
if you sow in a seed tray you are going to have to pot on, so be very careful. They need pinching out, so you get a bushy plant rather than a leggy one.