Posted: 04/04/2016 at 17:59
They're always a problem Fishy
I find putting smaller plants (I know the size of the Asda ones you've got) into a deep clematis pot for a while lets them get a bit of growth on and a decent root system, so that they are sturdier plants to plant out in a bed or border. It's easier to keep slugs away from them in a pot as you can protect them more readily, especially if you don't like using pellets.
I bought a few that sort of size two years ago, potted them up as described till late summer and then planted them out. By then, they were good sized plants and have gone from strength to strength.