after putting mine out at whatever they were 14"-16" mostly, they doubled in size easily. both in height and girth. cold frame is not a real option for me as it is still snowing some days while they are vegging indoors. i pushed it very early this year and put some out around may 10th i think. they had to be covered in burlap with tomatoe triangle stakes for support a couple nights. which made for a few tough days work.