it must be at least 10 feet tall before it will even think of flowering - it will flower between May and July and it likes FULL sunlight - Ken

Hmm...buds mean that it is thinking of blooming, though, Ken. What happens to the buds, Hillier? Late frost? Wind? In a pot and allowed to dry out? Those are the most common causes.

I'm amazed you can grow it in Sheffield as the winters can be so cold as I well remember. Very best of luck with it and I do hope it flowers for you next year.

Hi, welcome to G o y, first of all, can I ask you which species of Mimosa you have, {there are about 400 species} and also, Acacia dealbata, and Albizia julibrissin, are commonly called Mimosa.
Mimosa are at best frost tender, whilst Acacia can be half hardy to frost tender, Albizia are frost hardy to frost tender.
Can you tell us where you're growing it, eg, in a greenhouse, indoors, light conditions etc, Derek.

Hi, either I didn't notice you said Gaulois, {astier?}, or it has been added, but either way, this is a variety of Acacia dealbata, which is half hardy, and flowers in late winter/early spring, but you have not told us yet, where you're growing it, Derek.