Some men fear the pocket square as well as the boutonniere, and this post is not for them. Others will dare to wear a square and find the flower a step too far. A third group likes either, but not together. But the usual list of great dressers wore them simultaneously.
If fear can be overcome, the principal obstacle to wearing a boutonniere is finding a fresh bloom in the mornings. Carnations are best. Choose red ones for day wear, or pink on sunny days, and ideally miniatures as the full-sized variety adds a non-trivial load to a light-weight summer lapel.
When there is a florist convenient to the morning's walk, the price of a single flower should be no more than a dollar (or some fraction of a euro). Often, in my experience, the person behind the counter will be so pleased to see the custom resurrected that she will make it a gift the first time or two.
Men in temperate climates will find that half a dozen plants in the garden or on the balcony will provide blooms most days year-round. And where the climate is not temperate, the serious hobbyist can glass in a small space for a surprisingly modest sum.
Fear not the boutonniere.