I specialize in dried and silk flower boutonnieres for weddings and prom. They are long lasting, make a great keepsake, and are very light… making them easy to pin on. Here is a tutorial on how I like to attach them.
Place the boutonniere on the left side of the jacket. I like to center it over the button hole on the lapel.
Pinch your fingers on the front and back of the lapel to hold it in place, and flip it over.
From the back, with the pin at an angle, slide the pin through the fabric, catch a bit of of the boutonniere, then back out through the fabric. My boutonnieres come with 2 pins, you can use 1 or 2 depending on how secure it feels to you. The second pin can form an X or go above or below the first.
With the pin on the back, it looks nice and clean, and shouldn’t poke any one.