Water thoroughly, then restrict water until the seeds germinate. Lightly cultivate the ground around each plant to keep them free of weeds. Water regularly, adding a weak solution of liquid fertilizer twice a month. Too much fertilizer will cause dark green leaves and few flowers. Deadhead blooms before the seeds develop to encourage further blossoms, but leave a few flowers at the end of the season to set seed for next spring.
Sweet peas grow best if planted in a different place each year.
But newer types hold their bloom most of the day, especially in cloudy weather. Favourite varieties include I. tricolor 'Heavenly Blue', a bright sky blue, and 'Scarlet O'Hara', a deep red. When danger of frost has passed, soak seeds in water overnight to soften the seed covering. Or start seeds indoors in individual eight-centimetre peat pots four to six weeks before the last frost date. Feed them twice a month with a diluted solution of fertilizer to keep them blooming until fall's first frost.