Crescendos/Diminuendo in Notes with Ties

Firstly, I want to use crescendo for a note played by trombone and I added ties between the notes to be played longer.
But whenever I add a crescendo, not heard any effect on it.
I guess that cresc. works for more than one notes and when they're not tied. So how can I apply it for just one note or is there any way to do it and if, how?

**If there is a topic about this or any help page, I didn't notice so If there's any, please inform me.