I was at Dobbies this afternoon and bought 12 primrose plants, them went to Homebase and bought 36 Viola plants. Couldn't resist them. For best results what size pots and how many plants to a pot? I think I put too many in a pot, you can't see soil for plants so I don't think they have a chance to grow. Any advice?
To be honest, you can plant them in any medium to large sized pot - it's really a matter of taste. Personally, I find really huge pots with nothing taller in than primroses or violas in them can look a bit bare - I prefer a larger shrub or something in the middle. But others really disagree! Just do what you think looks good - it's you who is going to be enjoying them, after all.
For a good display, you can pack them in to some compost-rich mix with only a little bit of visible earth between them. However, if you do this, you'll need to move them out again once they've finished flowering - ideally to a shaded bed in your garden where they can rest over the summer. In the wild, primroses grow at the edge of woodland, so you want to replicate those conditions: moist, dappled shade. To be honest, I wouldn't leave them in the pot over the summer - it'll dry out very easily and they will not appreciate that.
Many kinds of primroses and cowslips are really, really easy to grow from seed, so it's worth gathering this and giving it a go in the autumn. I have a whole tray of cowslips that I've sown this way for the coming year.