Silly question about plug plants
I dug out two new borders earlier this year and to fill them at a relatively low cost I ordered some plug plants. I knew they were going to be small but when they arrived they were barely 3cm tall. So I've potted them all up and put them in the greenhouse and they seem to be doing okay. My silly question is, how long do I need to wait before I can plant them out in the borders? How tall do they need to be? They are all cottage plants perennials if that makes any difference. Thank you.