I recently cut a bouquet of ‘New Dawn’ roses and looked around my garden to see what I could put in the vase with the pale pink blooms. Finally I cut some oregano that was not yet in bloom.
I have often used it when it was flowering, but even without flowers it worked well as it has long stems and neat green leaves. The textured grey leaves of culinary sage also enhance flowers of any color. Mint too makes a wonderful companion for cut flowers, as it smells so fresh and clean.
I love to grow feverfew, Chrysanthemum parthenium, in my garden also because it is such a good filler in bouquets. The scent is not great, but the tiny white flowers are serviceable in a bouquet as well as in garden beds. I combine it with flowers such as monarda, lady bells, marigolds, and even knock-out and fairy roses. The lacy foliage, as well as the clusters of white flowers, makes most companion flowers look romantic. It is especially good in small bouquets, as it creates the impression of what the Victorians called a tussy-mussy.
The more you cut feverfew the more it comes back and re-blooms. When it self-seeds, I dig up the small plants and tuck them into corners of other beds. Experiment with herbs such as the red-veined sorrel, bronze fennel, catmint and cilantro, especially when it has its dainty white flowers. Just about any herb you grow can be used as filler to increase the impact of a few garden flowers in a vase.