Compost for jumbo plug plants?

[ScribblingPixie]

I've bought some jumbo plug plants online - echinacea - and it says on the instructions to plant into 1 litre pots (I've never done this before & was expecting plants I could put straight in the ground). It says don't use multipurpose compost. The only other thing I've got is John Innes No3 - oh and some compost I made but that's not great. Would any of these in a combo be ok? Thanks for any advice.

No 3 is really for mature plants, you should really use 1 or 2.

Did it say why you shouldn't use a multipurpose? I would rather use that than the no 3.

No, it didn't say except that they stocked some recommended compost - too late once the plants have arrived for that though. What I've done is had a look at the No3 and, yes you're quite right, it didn't look like it'd be ok. So I've sieved a load of my own compost and I'm going to use that. It was better than I thought down the bottom, just lots of bits of wood to get rid of, so hopefully that'll be ok. Thanks for the advice.