I have not been taking my tender plants in at night as the risk of frost has been very low given the warm weather we have had. It is my risk but it has paid off so far. Keep an eye on the weather forecast and decide if you want to plant some now and keep the others in a pot to bring in if frost is due.

Mid May is the normal date for last frosts - it snowed this time last year!

You haven't said what the plants are - if they're tender, then Kildermorie's advice is good. If they're not tender plants, but just needed hardening off because they'd been inside or under cover, then you can plant them out now.

I have been leaving my tender plants out overnight for a few days now, but always checking the weather forecast and mistrusting very clear skies. Any threat of a cold night and I will bring them in. Frost now would be surprising but always possible.