An easy-keeping plant, Knautia 'Thunder & Lightning' is a fun perennial that consistently sells on the strength of its two ornamental roles: bold variegated foliage and a deeply magenta flower that blooms over the summer. The plant has a low and wide habit in the garden, sending pincushion flowers up tall wiry stems.
The plant's primary appeal runs from early spring when it emerges until frost, when it finishes the display and disappears into the roots. Its wide stance fills the volume above the soil 12-18 inches for the entire time. Surprisingly the foliage is soft, even though the leaves are deeply serrated. Creamy margins run the length, easily seen from a distance and impressive in a mass planting.
When the soil warms up and the butterflies come out, tall summer flowers with a long blooming season make up the plant’s second point of appeal. Dark magenta pincushions are about the size of a quarter and held up above the foliage. They also work as cut flowers, fresh or dried, lasting a long time in a vase or bouquet.
'Thunder & Lightning' makes a striking specimen on the retail bench, in or out of flower. It has straight up garden appeal, and as a décor perennial it’s effective in clay or ceramic pottery as a specimen or a component in mixed combos. In the landscape its clump-forming habit knits into a mass planting for a full season of texture, with the added bonus of a summer floral display.
Seed heads add a nice touch in winter. If you leave the flowers on their stems they become a food source for birds in the colder months. During the summer, the flowers are platforms for butterflies and bees to collect pollen and nectar. Fortunately, the foliage itself isn't very tasty — deer and rabbits leave it alone.
Grow the plant in sunny areas. It can handle minor amounts of shade, sits well in standard garden soil, and doesn’t mind a bit of alkalinity. 'Thunder & Lightning' does need regular watering, especially during dry spells. Hardy to zone 5, it has a heat index of 8 but is vulnerable to wet soils that don't drain well. If the ground puddles after a storm, the roots will have trouble. Mature plants can be divided after 3 to 4 years.