polyanthus primrose primula

Primroses grow easily from seed - they spread like mad in the wild along hedgerows and the like.
I brought one seedling home from a holiday in Cornwall and now have them popping up all over the garden

Perhaps that means that the seed needs to be fresh, rather than from a packet..
I'm not sure about the others, though.

Prims need either to be germinated from very fresh seed, or ideally stored in the fridge until sown.  A lot of woodland plants are like this and the seeds enter a deep state of dormancy if treated otherwise.  I've tried cowslips and native prims from the 50p seed sales and had no success, but a cold treatment may well break them out of dormancy.

The native prims and cowslips self seed all over, the fancier polys and prims don't tend to and the seeds are pricy for all of them.  If you want native plants, it may well be cheaper to buy a couple and let them self seed 

I've grown polyanthus from seed a few times. They do prefer to be a bit on the cool side for germination, so I've sown in March, and they've always grown well. Some plants do better than others, but I've always had 30 - 40 decent plants for bedding. It's always fun to see what colours you've got when they flower. They do best the first year, although I've also lifted, split and saved them for a second year. After that it's best to have a break or the vine weevils build up.