Red valerian (Centranthus ruber) is a clump-forming herbaceous perennial native to the Mediterranean Basin. Also commonly called "Jupiter's beard" or "keys of heaven," it is an attractive garden plant as it displays lots of fragrant clusters of blood-red flowers from late spring into midsummer. It grows up to 3 feet tall and matures into a 3-foot-wide clump and drops seeds that sprout freely. It becomes naturalized, resembling any native wildflower, across U.S. Department of Agriculture Hardiness Zones 5 through 8.
Red valerian freely flowers and reblooms across the growing season, making it an alluring plant to add to perennial borders by gardeners, especially those who love to attract bees, butterflies and hummingbirds. According to reports from the United States Geological Survey Biological Resources Division, this perennial is naturalized across much of the temperate parts of the globe. In California, this species is being closely monitored as a noxious weed.
Red valerian prospers in a wide array of soils and rainfall regimes. It also flowers heavily and is so readily pollinated that it produces and scatters thousands of seeds across a landscape. These seeds germinate and survive on nutrient-poor and relatively dry soils, quickly choking out habitat for desirable garden plants or native plant seedlings. It also grows successfully in alkaline soils, unlike many garden ornamentals.
Seedlings of red valerian are easily pulled up by hand or killed by hoe cultivation. Gardeners who insist on growing this perennial in the hot, dry areas of their properties deadhead spent flowers before they develop into seeds. Deadheading is cutting off old flowers once they wane. This practice diminishes seed production and results in a secondary blooming cycle.
If red valerian does escape cultivation, its success as a naturalized weed/wildflower is limited by natural factors. For example, this plant does not grow in poorly drained or wet soils, highly acidic soil or where there is too much shade, according to the American Horticultural Society's "A-Z Encyclopedia of Garden Plants." Researchers with the U.S. Geological Survey comment that red valerian does not grow as quickly or vigorously where the summer growing season is humid and/or accompanied by ample rainfall (such as in the American Southeast). Where summers are dry, this perennial is much more prolific.
Overall, red valerian plants are rather short-lived, naturally reducing vigor after three to five years. In a garden setting, people dig up and transplant parts of the root rhizomes to rejuvenate into new clumps. Or, they allow some seedlings to grow and replace old plants that diminish.