Culver's root, a close relative of veronica, looks like a larger version of its relative. Lance-shaped leaves form on the lower stem, and densely packed spikes of flowers bloom in late summer and early autumn above the leaves.
- Common name: Culver's root
- Botanical name: Veronicastrum virginicum
- Zones: 3 to 8
- Size: To 6 feet tall
- From: Native to areas of North America
- Family: Scrophulariaceae (foxglove family)
- Sun: Full sun or partial shade
- Soil: Moist, well-drained soil rich in organic matter is ideal. The soil must drain well in winter.
- Moisture: Water during times of drought.
- Mulch: A 2- to 3-inch layer of mulch around the plants will help conserve moisture and prevent the soil temperature from rising too rapidly, especially in warm-summer areas.
- Pruning: Cut down dead stalks in autumn after they freeze or in early spring before the plants begin to grow.
- Fertilizer: In soils rich in organic matter, fertilizing isn't necessary. In other soils, use a general-purpose fertilizer in spring.
- Staking: To stake tall plants, sink a tall stake into the ground a short distance from the plant (so you don't harm the root system). Tie the plant stem to the support using a figure-eight pattern, with the stem in one loop and the stake in the other. This technique helps prevent excessive rubbing, which can cause open wounds and disease problems.
- Seed: Sow seeds in late spring when temperatures reach 60ºF. Don't cover the seeds; they need light to germinate.
- Division: Divide Culver's root either in spring or autumn.
- Aphids: These small insects often appear in large numbers on new growth. Spray them off daily with a stream of water; they will not attack a plant after being knocked off. Use an insecticidal soap or neem-oil spray if infestations are severe.
- Fungal disease: Fungal diseases may occur if the plant is in excessively wet soil. Once a plant is infected, fungal diseases are difficult to eradicate. To prevent fungal diseases, maintain good air flow between plants, put plants in a spot with well-drained soil, and keep the foliage dry. Destroy any infected leaves that fall to the ground.
- Leaf spot: In summer or autumn, the leaves develop yellow or dark-colored spots with concentric rings around them, forming a bull's-eye pattern. To deter it, prune the plant to maintain good air flow and avoid wetting the foliage in afternoons and evenings.
- Powdery mildew: Affected leaves develop a gray powdery covering and drop off. To deter the disease, prune the plant to allow good air flow and avoid wetting the foliage in afternoons and evenings
- Veronicastrum virginicum: Grows to 6 feet tall with spikes of pale pink flowers in late summer and early autumn. Zones 3 to 8. Native to areas of North America.
- Veronicastrum virginicum album: Grows to 6 feet tall with spikes of clear white flowers in late summer and early autumn. Zones 3 to 8.
- Veronicastrum virginicum ‘Apollo': Grows to 6 feet tall with spikes of lilac-pink flowers in late summer and early autumn. Zones 3 to 8.
- Veronicastrum virginicum ‘Spring Dew': Grows to 4 feet tall with spikes of white flowers in late summer and early autumn. Zones 3 to 8.