I would have thought they would have been hardened off to cold greenhouse level already Cooky but these are very hardy (USDA zone 3). Just in case they have been grown in warmer conditions (but I can't see why) just give them a week in the g.house then put them out for a couple of days then plant..

Put them out during the day for a couple of hours put them back in the greenhouse afterwards, then increase gradually the time you leave them out during the day over, say, a week or two (depending how cold it is) and then leave them out overnight, by which time you can plant them out.