you have to grow sweet peas every year i think youl find but there quite easy to grow .

There is a species of sweet pea that is perennial, Sheila. (Lathyrus latifolius). As far as I know it just has one colour - pink!
For the annual varieties, many sweet pea growers start their seeds off in the autumn and keep them in a cold frame, "Don't coddle them" is the advice here - http://www.sweetpeas.org.uk/how.htm

So I guess they are hardy annuals. Perhaps if they have been kept warm they'd need careful hardening off. If they've been outdoors all winter, no need to worry!

Lathyrus latifolius is hardy perennial, along with a couple of others, but L. odorata varieties are not, they're hardy annuals. you can move them outside after hardening off end of March/April

The Sweet Pea seeds that you buy in packets from the garden centre are not hardy (are they annuals?) but there are many varieties of Lathyrus that are. Some are climbers, some are shruby. We grow a very nice herbacious shruby variety called L. vernus. These perenials are worth looking out for, Sheila.

Many thanks . . . yes, the friend who asked me has the annual ones in her cold frame, so I guess they are sort of in the process of being hardened off. She was so pleased that they germinated, that she doesn't want to lose them! I will give her your advice, so thank you very much.

My sweet peas have been growing outside in an open cold frame all winter, only being closed when temperatures went below -5c.
I planted them out today.

I have a hardy variety of sweet pea

http://www.flickr.com/photos/31559373@N00/3617437470/

I have 2 types of hardy ones that stay in the ground all year round, the shrubby Lathyrus vernus that Bulbaholic speaks about and the climbing type Lathyrus latifolius that Beattie and Bamboo speak about.

There is a white one aswell as pink, Beattie, that's the one i have (white) , it grows with a pink rose on an obelisk.

Thank you all. I have just read Scrumpygraham's sweet pea blog . . . brilliantly helpful! I will pass on the info to my friend, and thanks again.

just updated it with a few more pictures and tips.