I love using decorative grasses when making boutonnieres. The graceful lines add a lot of visual interest. Bear grass is thinner and more slender. Lily grass (shown below) has wider and stiffer blades with a smooth, deep green finish.
Decide how big a loop you want to place behind the two flowers.
I'm going to go with a tighter, more closed loop so that the finished design will not go off the tux lapel.
DIY brides are sometimes surprised to learn that florists use basic tools like office staplers to secure greenery and leaves into place.
A single staple secures the grass into a permanent loop that can be taped behind the assembled boutonniere.