I have four years old royal empress. Why is it not flowering.

Question

Its more than 10 feet.

Answer 1

I found a publication that says they don't start blooming till they are 5 to 7 years old. So you are almost there! The flowers are formed in the fall, so do any major pruning in the spring after flowering.

https://www.uaex.edu/yard-garden/in-the-garden/reference-desk/trees/empress-tree.aspx

https://www.gardeningknowhow.com/ornamental/trees/royal-empress/pruning-empress-trees.htm