Not really. You can these days buy and plant pot grown perennials almost all the time. In fact if you have the patience it is often a good idea to buy them in flower as that at least gives you an idea of what they look like, when they flower and if they are what it says on the label.

i shouldnt think so Squirrelhall.Quite a lot of people buy their flowering plants now to give them something to do over the bank holiday weekend

thanks very much for you quick response - on our way to garden centre now

i hope not as i have loads still to get in the ground.

so yes you canm plant from pots any time unless the ground is frozen.

I often have a look round the big DIY stores' garden departments AFTER the bank holiday week-end as they often start to unload unsold stock then at reduced prices. It's not too late to plant but make sure they didn't forget the watering as quality varies.