Posted: 13/02/2017 at 15:19
Though hardy the one thing that sweet peas don't like is cold biting winds, they can get severely knocked back. If they're autumn sown they should be OK to go out mid to late March after they've been properly hardened off.
To protect against harsh winds you could create a wind break using fleece. This will protect them until established.
Just make sure that the soil is well enriched with organic material before planting.