Let them grow a little bit taller...say 1-2 inches more..then snap off the main stem near bottom ( leaving 4-6 pairs of leaves)..pot them on in 3 in. pots using multipurpose compost mixed with plenty of perlite or grit...keep them watered, fed and let them bush out (that's why you need to snap the leader).
When they have filled the pots pot them up again 6-8 in. pot or in green house border...and there you are..provide some form of support to keep flower stems upright and you'll end up with lovely cut flowers.
If you are after show quality blooms...well then there is more to it...
