Blue is consistently the color that intrigues humans most, perhaps unsurprisingly because true blue is one of the rarest shades in nature. That rarity gives blue its allure.
In the garden, blue is a charismatic color, saturating our imagination with dreams of beachfronts and the afterlife. It is perhaps most magnetizing in summer, when it’s more unexpected than in spring. The catmints (Nepeta) inaugurate summer about as well as any blue-flowered perennial. Sure, they verge on lavender, blending shades between cultivars, even venturing into white and pink, but clouds of their classic flowers make up for a lack of color purity. Everyone knows and grows ‘Walker’s Low’, and nobody argues that it’s earned fan-favorite status. But there’s more to catmints than sprawling blue mounds that flower forever until nobody notices them anymore. Newer varieties like ‘Blue Lagoon’, showing the influence of ultra dwarf N. racemosa, have sized down the same effect into something lower growing with frosty green leaves and plenty of blue flowers (note: the name ‘Walker’s Low’ refers to the garden the plant was found in, not anything to do with its habit).
Many catmints in fact grow up instead of out. Some gardeners, mostly cat lovers, seem to find ornamental (or maybe it’s purely pragmatic) value in growing Nepeta cataria, the wild catmint usually thought of as a weed. Believe it or not, cultivars exist, including ‘Citriodora’, which puts on quite a show of grayed lavender flowers (and has, as its names suggests, a citrusy smell). Nothing blue here. But if you’re thinking blue (lavender blue) and upright, you should plant the bone-hardy Siberian catmint, N. sibirica, particularly ‘Souvenir d’André Chaudron’. At nearly twenty inches tall and wide, it takes on a striking midsummer role in the perennial border with fragrance that isn’t atrocious (at least to this human), as some catmints are. ‘Souvenir d’André Chaudron’ is strikingly similar to N. yunnanensis but with less of a habit for running and reseeding and more hardiness. The Japanese native N. subsessilis is quite nice, stockiest in habit of any mentioned here (up to thirty inches tall and half as wide) and with the darkest flowers. I’d love to see more breeding in catmints, but with so many fine examples, what stone is really left unturned?
“Plants are notoriously difficult to germinate from seed, and many species are monocarpic, meaning they grow, flower, set seed, and die. Jerks.”
Now for something truly blue—the Himalayan blue poppies (Meconopsis) of horticultural fable and lore. Volumes couldn’t fully extol the obsession verging on lust that gardeners have had for these cover girls throughout history. Plants are notoriously difficult to germinate from seed, and many species are monocarpic, meaning they grow, flower, set seed, and die. Jerks. (At some point everything dies, but it’d be nice if they’d pay the rent more than once.) Neither characteristic has stopped plant hunters from traipsing into the wilds of Asia to describe and collect them. In the garden, the trick is mostly related to climate—cool, moist shade with a few hours of morning sun and no sweltering heat or humidity in summer, something of fiction for gardeners anywhere south of the Great Lakes or outside the Pacific Northwest. For the ultimate plant envy, visit gardens near Seattle or Vancouver or Quebec City (particularly Les Quatre Vents, known for M. betonicifolia by the thousands). Some things just aren’t fair. If you’re lucky enough to call these regions home, load up on organic matter and give them a shot. Fine strains exist, particularly ‘Lingholm’, a hybrid of M. betonicifolia and M. grandis with good perennial staying power, at least in the Edenic places amenable to their cultivation.
While long suffering from the reputation that they are difficult to grow, gentians have more in common with Rodney Dangerfield than Michelle Obama, and that’s a pity. With nearly four hundred species from all temperate corners of the world, gentians can be anything from bog dwellers to scree settlers. Across eastern and central North America, many species of bottle gentians (Gentiana andrewsii, G. clausa, G. catesbaei) call wet prairies, woodland edges, and savannas home; few, however, seem to cross the garden fence into similarly styled planting areas.
“While long suffering from the reputation that they are difficult to grow, gentians have more in common with Rodney Dangerfield than Michelle Obama, and that’s a pity.”
In late summer and fall, when their remarkably pure colors rage against the dying summer, gentians rule. For starters, ‘True Blue’, a hybrid from master plant breeder Darrell Probst, is among the finer new perennial releases in the last decade, despite its limited offering. The breeding behind ‘True Blue’ seems to have thinned out the fussiness of the species, while only amping up the blue rage with more intense color and larger flowers. A hybrid of G. scabra, the familiar rock garden gentian, and G. makinoi, a cold hardy Japanese species, ‘True Blue’ grows best in fairly normal garden soil and rockets into flower atop eighteen-inch stems starting in late summer.
If you have a knack for hypertufa troughs, the gentian palette offers plenty of choices. Any legitimate rock garden has at least a dozen forms of Gentiana acaulis (trumpet gentian), often due to their tendency to reseed into the gravel scree. While short and squatty, nothing dulls the brassy blue calls of a dozen flowers open at once. In spite of their rarity in gardens, trumpet gentians grow readily if given good drainage and bright exposures, and they weather drought with nary a missing flower. Urs Baltensperger of Edelweiss Perennials offers the best hybrids in the United States, selected for compact habits and luscious flowers, among them ‘Renate’ and ‘Maxima’.
Gentiana septemfida is another of the dwarf gentians that thrives in more places than G. acaulis seems to. Readily adapted to hot summers in the Midwest and South, it’s a welcome puddle of color in mid- to late summer. Avoid planting where taller plants would shade it out.
Salvia does blue as good as any genus can. In milder climates, S. patens, with its many large, claw-shaped flowers, borders on essential. Then again, in milder climates the salvia choices in general abound. Salvia mexicana ‘Limelight’ has a mile-long list of endorsements from esteemed plantsmen and garden designers. At six feet tall and wide, a well-grown specimen explodes with endless spires of blue flowers surrounded by lime green calyces. Cut them for bouquets and watch more stems replace them. It won’t stop! The ultimate zinger plant—nobody will miss this: it’s a must-have perennial in zone 8 and above and an annual worth containerizing in colder climates.
Not all that’s blue in salvias is left to warmer climates. Apart from the purple-blue hybrids of Salvia nemorosa that are abundant in gardens already (especially so thanks to their role in New Perennial Movement plantings in public spaces), several hardy blues are missing, among them S. azurea. Another late summer, often fall flower, azure sage pours out the flowers—a watery metaphor for a species that doesn’t need water. It thrives on hot, dry sites, perfect for hellstrips and bygone alleys where concrete is more prevalent than chloroplasts. It’s certainly more interesting than Russian sage (Perovskia atriplicifolia), but azure sage does have a tendency to flop in gardens, often because it’s fed too well. Grow leanly and without charity. Nebraska plantsman Harlan Hamernik selected ‘Nekan’ north of Lincoln, a fine cultivar with lithe stems, tough constitution, and blue flowers up and down three-foot-tall stems.
If wetter planting sites prohibit planting fall-fabulous Salvia azurea, Lobelia siphilitica, the great blue lobelia of wet woodland edges and sloughs, would grow just as well. A clumper by habit, it thrives in consistently wet soils—the September highlight of the bog or water garden edge.
On a more Mediterranean note, Agapanthus sings the blues happier than anything I can think of. Visually these plants are the perfect contrast—blue and dramatic, yet blithe and abounding. And while a few are white, deviation from the color norm doesn’t change the point—in the open border or even containers, these things are fabulous. With so many varieties offered, it’s hard to know where to start. ‘Storm Cloud’ and ‘Summer Skies’ gleefully take center stage in whatever large container you can find for them, handsomely accenting perennials with darker, moodier foliage to fashionable effect. The newer ‘Queen Mum’, a silver-headed ball of awesomeness, is destined to capture attention. I imagine them looking regal planted along a walkway or promenade, royally greeting everyone that strolled by. My hands-down favorite agapanthus, however, is A. inapertus ssp. pendulus ‘Graskop’, down but not downcast, beloved for its drooping flowers that are anything but Eeyore.
Kelly Norris is a horticulturist, plant breeder, and plantsman who lives in Des Moines, Iowa. In addition to being the award-winning author of three books, he is the director of horticulture at the Greater Des Moines Botanical Garden, a revitalized 14-acre public garden. He and his family also own Rainbow Iris Farm.
“Guides us away from boring plants and directly to vibrant, jaw-dropping, stylish plants. . . . bring your garden into the 21st century!” —Garden Design