Annuals can do more than fill gaps in mixed borders. Using those with subtle colors and beautiful form makes annuals an integral part of the garden’s design.
I think of myself as a purist, so when I started my perennial border some years ago, I wanted nothing but perennials. After all, I reasoned, a perennial border should contain only perennials, shouldn’t it? But, as time went by, I added several compatible shrubs to my garden and began calling it a mixed border. That new definition liberated me to add a few annuals. Even so, I felt a lot less conscience-stricken when I learned I wasn’t the first to use annuals in a perennial border. My gardening betters had paved the way long ago.
Ever since the introduction of the herbaceous border in the days when William Robinson and Gertrude Jekyll ruled most of the known horticultural world, it has been considered legal to fill in gaps in a perennial or mixed border with annuals. It is almost inevitable that dull areas—and even blank, empty spots—will occur in a perennial border as the summer wears on. Perennials with nothing to contribute but their blooms stop blooming. Then, there are those perennials that are subject to unsightly afflictions if the summer is too wet—or too dry.
Even when you carefully orchestrate the garden so that delicious combinations of color and texture will provide an ever-delightful symphony from early spring to late autumn, those annoying gaps will occur. Perhaps rabbits ate the blue star (Amsonia tabernaemontana) or deer the delphinium. Maybe the wildly changing spring weather did in some of the roses. Whatever the cause, your symphony has been deprived of important notes and, in some cases, whole themes. It’s then that you need annuals.