Dr. Leonard Perry, Extension Professor
University of Vermont
The common name of Culver’s Root doesn’t do justice to this tall, native perennial that blooms with generally lavender spikes in mid to late summer. Although grown mainly ornamentally now, this plant may be named after a pioneer physician who advocated use of the root medicinally.
Another member of the figwort family like the speedwells, Culver’s root differs being taller, with whorled leaves, and generally unbranched except at the flowers. There is generally only one species (Veronicastrum virginicum) found for sale, along with several cultivated varieties or “cultivars”. Flowers are very attractive to bees and other pollinators such as butterflies, so they are good for wildlife gardens but not to place next to a walk or patio.
Being 4 to 5 feet tall, they are good for backs of borders or in the centers of island beds. The statuesque habit makes them good as a focal point. Or interplant them with upright ornamental grasses for a prairie or meadow garden. Interplant some of the new tickseeds (Coreopsis) underneath in a mass. The color blends nicely with Russian sage, or contrasts with many of the red and pink bee balms.
Flowers appear in mid-summer, lasting into August in northern gardens, and resemble upright candelabras. The central flower “spike” is surrounded by a whorl of secondary spikes that bloom next, and then flower spikes from the leaf axils where leaves join the stems. To get a more full cluster of flower spikes, pinch out the central spike as it’s forming. These make good cut flowers, picked ideally when flower spikes are about one-third open.
Over a 5-year period, Richard Hawke at the Chicago Botanic Garden (USDA zone 5b) conducted a trial of over 7 selections to determine how they perform in northern gardens. Of these, 4 rated good and 3 rated poor due to less flower production. The top rated included ‘Apollo’, ‘Fascination’, ‘Lavendelturm’ which usually is seen as Lavender Towers, and ‘Pink Glow’. All but the last have lavender flowers, the latter being pale pink and blooming slightly later than the others. The 3 cultivars with fewer flowers were ‘Pointed Finger’, ‘Spring Dew’, and ‘Temptation’.
Although ones I have grown in my Vermont trials have remained upright, without staking, and in good health, those in the Chicago trials had lower leaves wither by late summer. Stems turned brown there, and then the weakened stems snapped off in the wind. This may relate to the wet soils at their trial site, and warmer climate. Cutting plants back to the ground in late summer produced abundant basal leaves.
Culver’s root prefers full sun and moist but well-drained soils. Too much shade and plants will lean toward the light, have fewer flowers, and may flop over so need staking. Add fertilizer in the spring, and again in early summer if plants seem to lack vigor and a good green color. Once established, plants tolerate some drought.
Results of trials on many other perennials can be found online under the Research section at the Chicago Botanic Garden (www.chicago-botanic.org/research/plant_evaluation/#notes).