Hi Sarah,
Firstly pinch the growing tip/tips out to make them grow more 'bushy' otherwise you will end up with one long stem. When you say they are growing in a 'flat' do you mean they are rooted cuttings in a flat tray which is divided into sections? If this is the case, carefully remove them and grow them on, each planted into a 3 or 4 inch pot, when you see the roots appearing through the drainage holes, then pot them up into your hanging basket. Night temperature must be no lower than 50f. - Kath :)

Thank you for the info. I'll pinch them like you said. Yes, they are divide sections on a flat. No, I guess it's not time to plant yet. It's still in the 30's to 40's at night in western washington. I'll wait a bit. Thanks again!