According to the author of The Boutonniere: Style in One's Lapel, wearing a boutonniere, or buttonhole, has never been particularly widespread. We see them today principally at weddings and specific occasions like Remembrance Day in the Commonwealth countries. Our days would be more pleasant if we saw them more often.
Some men probably fear the attention that might come with a buttonhole just as they fear the pocket square. To them I say that there's no need to push the envelope. Think of wearing a buttonhole as a replacement for a silk square, to be worn under the same circumstances. You'll be glad you did.
For day wear, avoid showy flowers in favor of blooms like red and pink carnations. Carnations, and their cousin the Sweet William, gained their popularity because they are among the very few flowers that remain fresh all day without water. Perennials, they are easily grown outdoors and bloom throughout most of the year in California. I have them in a box on my balcony in the City so I can cut one whenever the mood strikes but there's no need to go to that much trouble if you only wear a flower once in a while. The majority of florists I've entered have refused my offer to pay for a single carnation and the rest have been happy with a dollar.
Evening blooms need to remain fresh fewer hours, and that opens up your range of choices. The evening combination of white and black is consistent with white orchids, gardenias, and white or red roses.
At a wedding, the flowers worn by the groom should complement what's in the bride's bouquet. That's often a lily of the valley or a small orchid. The bride's father and the best man wear the same flower as the groom, and the ushers usually wear carnations, sweet peas or small white roses.
Of course, to wear a flower, your lapel must be prepared for it. Never pin a flower to your jacket. The lapel requires a buttonhole that's about an inch and an eighth long, so the base of the flower fits into the space and observers will see the top of the bloom rather than the side. The photo to the left shows the back of the lapel of a Fallan & Harvey suit, with the other necessity - a silk thread to hold the flower stem in place.
If you're one of those men who have open buttonholes on your jacket sleeves, make sure your tailor is also preparing your lapel. It's an inexpensive way to add elegance to your day.