Yarrow and I go way back. In fact, it was among the original dozen or so perennials that I planted in my first real garden more than 20 years ago. Sure, it was a gawky, rather unruly specimen with dirty, wine-coloured blooms, but even in my salad days, I recognized that it never needed extra water, possessed exquisitely intricate foliage and stayed in flower much longer than my other perennials. Today, this Cinderella plant can be had in myriad colours, shapes and sizes, all of them well behaved, hardy and well deserving of a prominent place in your sunny border.
Although most gardeners recognize yarrow when they see it, few realize what an intriguing, varied past it has. From the teapot to the witch's cauldron, throughout the ages, yarrow (Achillea spp.) has been there, done that. Legend has it that it was named after the Greek hero Achilles, who used the herb's antiseptic leaves to bandage his soldiers' wounds at the Battle of Troy. Certainly its ancient Roman name, Herba militaris, reinforces this martial association.
A member of the Asteraceae (or daisy) family, each yarrow bloom is actually a collection of many individual flowers arranged in a flat-topped cluster called a corymb (much like those of candytuft or sweet cherry). This is just the sort of arrangement that suits butterflies and beneficial insects alike, whose mouths find the tiny flowers a perfect fit and which, once well fed, will help thwart the advances of countless garden pests.
Yarrow blooms at the height of summer, just a week or so after the first flush of roses. Its flowers last for three to four weeks, and while assiduous deadheading will encourage secondary flowers, I prefer to let them bloom once, then shear the flowering stalks down to the basal leaves. This technique produces a fresh set of blooms in early autumn, just when the flower-starved garden really needs them. Almost all varieties have finely divided, segmented leaves, reminiscent of feathery fern fronds. Some are green, while others are silvery grey, making the plants attractive and interesting throughout the season. Most yarrows are hardy to Zone 3. Yarrows require full to part sun; good drainage around the root zone is essential, so if you garden in heavy clay, add plenty of leaf mould and horticultural sand to your planting holes. The Achillea genus also prefers a lean diet; adding a lot of well-rotted manure or rich compost will only result in more foliage than flowers, and what blossoms you do get will inevitably flop and topple over. Too much shade will also cause floppiness and fewer blooms. There are no serious pest or disease problems, and named cultivars rarely self-seed. Overgrown clumps are easy to divide in spring or autumn.
Nevertheless, as with most truly robust, carefree flowering plants, there's a downside: some wild forms of Achillea can become invasive, particularly the species A. millefolium, which has long been the bane of farmers. Ironically, this species also supplied gardeners with some of the choicest, best-behaved cultivars in the genus—and it's a good thing, since this is where they inherit their genes for cold-hardiness, vigour and drought tolerance.
Most species of Achillea grow throughout the temperate regions of the northern hemisphere, making them certifiably native to many countries, including Canada.