Rock garden plants generally do not need or want a rich soil. They tend to get too big and short lived on a rich diet. What you should be adding is 5mm grit. My favourite soil is, by volume, 1 part garden soil (preferably sterilised, but obviously if you are taking it from the garden it won't be) 1 part peat free seed compost or fine grade composted bark and 1 part 5mm grit. The grit really should be crushed granite rather than limestone.

I agree with Owdb. rockery plants do not want a rich soil, they grow in poor impoverished soils and shattered screes in their native habitat.

Nikki, sometimes people think a rock garden is the same as a rockery and they're not.

A rockery, as explained above, needs no or thin impoverished soil.
A rock garden - where you might plant hebes, conifers etc. - is a completely different animal and would need the soil you have in the rest of the garden.

A rockery will need decent amounts of sun and be VERY well drained.
A rock garden can be any aspect and free draining isn't particularly important.

I have a rock garden in my front garden Large rocks and crushed plum slate .

And the plants grow well.

Not in bloom just now covered in frost I shall post a photo later.

Strangely the plants mentioned by Louise all do better in well drained, not too rich a soil.

I agree Owdb.

Hey ho !
I see them in peoples rock gardens with earth up to their ears !

Doesn't mean it is the best habitat for them.

Indeed.