Sow sweet pea seeds indoors in October into individual cells or small pots. Seal inside a polythene bag until germination, then immediately remove to prevent fungal rots. Overwinter in a cold frame before planting out 9ins apart in spring. Sweet pea seeds can also be sown outdoors in the spring, 1 inch deep in to a prepared seed bed. Pinch out the growing points once the second pair of leaves has opened. Dead head regularly to encourage new blooms.