Sow seeds outdoors early, as soon as the soil can be worked. Sweet peas only thrive in cool months, don't delay when planting them. Prepare garden bed with plenty of compost or manure. Provide sweet peas with good support, they will grow as high as 6' if given proper support, water and fetility. Harvest flowers often to encourage more blooms. If given a good start, sweet peas will keep blooming into the summer months.