There isn't a hardy Mimosa LadyE....Do you mean Mahonia by any chance ?

Acacia dealbata would be the best to grow but like many other 'hardy' shrubs many have not survived the last two winters. Could survive in very sheltered gardens. Best purchased as fairly mature plants. Would take years to grow from seed if lucky. Could try cuttings.

I was going to break the bad news too, Jimmy/Pimpernel. In a village near here that I drive through frequently, there were two beautiful mature Acacias, sheltered against a South facing wall. One died last winter, and the other suffered really badly - it won't get through any more frosts.

Don't believe any GCs that tell you they're hardy, with the winters we've been through and possibly another to come.

The closest you'll get to 'mimosa' that's hardy in this country will be Mahonia aquifolium 'Apollo'.

I have a fantastic looking robinia pseudoacacia which is as the name suggests similiar to acacia.Although it hasnt produced flowers (dont know if it will) it is reasonably fast growing and truly hardy.Ihave added a picture of it to the photos on my profile if youre interested.

Dgw- if your tree decides to flower, it will produce white racemes of flowers - unfortunately, nothing like mimosa!

Robinia Pseudoacacia (False Acacia) 'Casque Rouge' will produce flowers, but unfortunately it grows to 15 metres. The bog standard Robinia pseudoacacia 25 metres and 'Frisia' 12 metres. I'm sorry to say that at present many of these are also dying due to a soil borne virus.

The Robinia also suckers a lot.

And is brittle and likely to drop lumps in a windy position...