lcoste, to make a flower 3D - you actually have to have a design that is made to be used this way - there are several out there - even a couple on this site. You do usually stitch the flower using water soluable stabilizer (WSS) - either on a fabric or it is Free Standing Lace (FSL). I generally use two layers of WSS when I am making FSL - use the same embroidery thread in the top and bobbin. I have used organza to do some 3D flowers and I just hooped the organza and didn't use WSS, but you have to be rather careful when you are working with organza, too. I used the same embroidery thread in the top and the bobbin on the organza flowers, as well.

You can't get better advice than what Shirlene gave you. Her lace is gorgeous. Have fun stitching your bouquet

thank you for your help

I embroidered 3D flowers on an apron - alas before I started taking pictures of all I stitched out. I did a number of daisies, stitched them on cotton on tear away end cut it back like an applique befor the final outline, left out the yellow heart of the flower.
Then I hooped the apron, stitched the flowers - one at a time - added the loose embroidered ones on top, them stitched the heart to finish them. Looked great andstayed lovely after being laundered many times.