Sweet peas are as popular as ever, and nowadays a wide range available, both old fashioned heirloom varieties and modern, long stemmed cut flower varieties too. Most of the flowers are highly scented and have a long flowering period, especially if taken care of (will expand on that a little later).
Sowing:
Many experienced gardeners sow the sweet pea seeds in the autumn (September-November) into a cold frame/unheated greenhouse and then plant them out later in the spring when the soil warms up a bit. This is not advised in the North of the country though. You better off sowing the sweet pea seeds in the spring, in March and then plant them out to their final position when the seedlings are 5-7 inches tall.
The sweet pea seeds have hard coats. To aid the germination the seeds can be soaked overnight before sowing. For most successful germination, crack the seeds a bit by rubbing them between two sheets of medium grid sandpaper and then soak them for about 10 hours. With this method you will crack the seed coat and the let the water in through the cracks before sowing into fine seed compost. This is not absolutely necessary, some studies show no difference in germination rate if you just sow the sweet pea seeds without any treatment and soaked seeds sowing. However this method will speed up the germination.
Sow the seeds about an inch deep into small pots. A propagator or a windowsill will be a good place to germinate the seeds, keep the temperature at around 15 Celsius. The seedlings should emerge in a week time and when they grow out of their pot, plant them into their final position. Grow them on in cooler conditions in an unheated greenhouse or coldframe.
Growing:
The sweet peas are climbers, so they will need some support. They like an open, sunny location and a fertile, well manured soil. In the autumn dig deep where you want your sweet peas, add lots of organic matter, a handful of bone meal, this way you will give the best possible start to your sweet peas. 
The most common method is to train the plants onto a wigwam built out of canes or build a row of canes, but any frame, trellis will do the job perfectly. If you grow the flowers for competition, it is a common practice by many that the side shoots and even the tendrils are snipped off. The idea is that the side shoots, tendrils and the flowers running to seed take energy which ought to be directed towards producing bigger and better blooms. And the sweet peas respond very well for such a hard job and will produce larger blooms. Combine this with regular feeding and you beat everyone at the local allotment show. If you remove the tendrils you will have to replace them by tying the plants to the canes, but you might have to do this job anyway to give the plants a better support. If you want a lovely display in your garden and some cut flowers in your home, there is no need to go to such lengths, enough to cut the flowers to encourage the plants to produce more fragrant blooms.
