Silk Tree

[Suej]

Hoping that someone can help.

I have a silk tree that i put in 3 years ago. The first year when I planted it there were flowers but last year and this there have been none   . It looks really healthy. I give it a good soaking once a week and gave it a slow release fertilizer in the spring.
Does anyone have any idea why it is not flowering, I've look through my books but can't find any reason... ???

Thanks Sue