I am putting my exhibition cordon trained sweet peas out now. They are hardier than you think and can stand a little frost. I do not protect my sweet peas with anything. My autumn sown sweet peas are already out on the allotment, although there are not that many because I lost a lot during the severe winter - they are not that hardy. Having said that some of last years sweet peas dropped their seed and these have germinated on the allotment.