Endearing little sprites that carry flocks of dainty, spurred blooms above clumps of ferny divided leaves, tuberous Corydalis (crested larks) are among the most valuable early-spring “bulbs” for shade. These low-growing perennials have long been known to horticulture: the most familiar of the tribe, Corydalis solida, has been kicking around gardens since at least the sixteenth century. But in the last few decades, a multi-hued array of new species and cultivars has entered cultivation, taking the genus into exciting new territory.
The genus Corydalis also has a non-tuberous side, comprising several dozen perennials or annuals that grow from fibrous roots (rather than from swollen underground stems) and that remain in leaf all season (rather than disappearing shortly after bloom). These fibrous-rooted corydali include several species that are well worth a place in the ornamental garden – among them Corydalis lutea (now Pseudofumaria lutea), known for its profusion of yellow blooms and self-sown seedlings; and Corydalis flexuosa, whose luminous blue flowers and notorious heat intolerance have caused much lusting and despair among eastern North American plant enthusiasts. None of them, however, blooms in in early spring in hues ranging from blue to purple to bright red to pale yellow to white. For that, you’ll need Corydalis with tubers – especially Corydalis solida.
Native to woodlands from southern Scandinavia to northern Spain to the Ural Mountains to northern Greece, Corydalis solida assumes a dizzying variety of colors and forms across its vast natural range. Until relatively recently, gardeners had to settle for the most common, rather nondescript purple-flowered forms. No longer. A wealth of cultivars in a broad and tantalizing range of hues now populate the pages of bulb catalogs. Among the oldest and most renowned of these new-wave corydali is the brick-red ‘George Baker’, one of a pack of red- and pink-flowered selections hailing from the mountains of Transylvania. (Caveat emptor – bargain-priced tubers sold under Mr. Baker’s name are often imposter seedlings bearing dingy-red blooms.) Other outstanding cultivars from the sunset side of the Corydalis solida color range include deep rose-red ‘Cantata’, rich lilac-pink ‘Sixtus’, and soft creamy-pink ‘Blushing Girl’. At the violet end of the spectrum are pale-lilac ‘Ballade’, denim-blue ‘Compact’, icy bluish-white ‘Evening Dream’, and the aptly named ‘Purple Beauty’. Milky-flowered ‘Snowstorm’ and the floriferous, late-blooming ‘White Knight’ are among the best white-flowered selections.
Most Corydalis solida cultivars readily self-sow (with the assistance of seed-dispersing ants), their seedlings often reverting to the muddy purple floral tones of the wild species. Remove such seedlings to keep them from crowding out their more colorful parents.
The world awaits a yellow-flowered Corydalis solida (reputedly such forms exist in the wild). Crosses with the sulfur-bloomed Siberian native Corydalis bracteata sometimes occur, however, their offspring (known horticulturally as Corydalis × allenii) producing pale creamy-yellow, lilac-brushed blooms and fetching, deeply cleft leaves. Corydalis bracteata and its fellow Siberian Corydalis gracilis also make excellent yellow-flowered garden subjects for areas that have long, cold, snow-locked winters.
Woodland Corydalis are habit-forming. Once you’ve discovered Corydalis solida and its hybrids, you’ll want to have a go at the many other garden-worthy species – perhaps Corydalis malkensis, with its voluptuous, gaping, swan-white blooms; or Corydalis kusnetzovii, which flowers in a beguiling shades of pale pink; or one of the brilliant-blue-flowered East Asian species (such as Corydalis ornata and Corydalis turtschaninovii). All thrive in partial shade and humus-rich soil; amend sandy or heavy soils with a good compost such as Fafard Premium Organic Compost or Fafard Canadian Sphagnum Peat Moss.
Real corydalis addicts will also want to explore some of the Central Asian species, which are typified by pink or white, chocolate-nosed flowers, blue-green foliage, and a preference for sunny, gritty-soiled niches that stay relatively dry in summer (such as a rock garden or trough). As with the woodland Corydalis, they present a wealth of delightful possibilities for the early spring garden.