Giving Seedlings the Cold Treatment

[gill_s]

Following the cold treatment advice I thought I would make a start last night, but to gradually reduce the temperature. I am using a propagator and have some additional greenhouse heating, but trying not to set the temperature for this higher than necessary. I set the propagator temperature(for soil temp) at 14C(57F). I put a max/min thermometer in as well as seedlings and the air temp got down to 8C(46F). In the other propagator containing the younger seedlings set at 17C(63F) the min air temp was 14C(57F).
It is obviously difficult to maintain a soil temp close the air temp without considerable extra heat in the surroundings. Of course if I choose not to heat the greenhouse any more the dilemma is whether I should set the higher soil temp for the 'cold' seedlings or for the younger ones! Any ideas?
Gill