Wednesday, January 20, 2010

Plant Care Profile: Red Valerian (Centranthus ruber)

Though commonly called red valerian, Centranthus ruber is actually only distantly related to true valerian (Valeriana officinalis) and is also known as Jupiter's beard. It is, however, a great perennial for sunny beds and borders which needs very little care and flowers almost continuously for much of the summer. Very adaptable, it can even grow in the cracks of of old stone walls and has apparently become naturalized in Great Britain as well as the southwestern United States, the Pacific Northwest, and Hawaii. The airy pinkish-red flower clusters are very attractive to butterflies and for planting schemes in which tones of red would not fit well there is also a white-flowered cultivar.
Centranthus ruber in the frontyard of my parents' previous home in southeastern Michigan

Origin: Centranthus ruber is native to the Mediterranean region.
USDA Hardiness Zone: According to most sources, Centranthus ruber is hardy to Zone 5a, and in my own experience it is hardy at least to Zone 6a.
Centranthus ruber growing in cracks in a retaining wall in the Katz'sche Garten in Gernsbach in southwestern Germany

Size: Centranthus ruber can reach up to 3' (ca. 90cm) in height, though the plant will often lean outward quite a bit and as a result remain lower. Individual clumps can reach a similar diameter, but if given less space they will usually remain smaller. Even though it is a fairly vigorous grower, Centranthus ruber will rarely overwhelm neighboring plants unless they are significantly smaller.
Flowering Time: Depending on the local climate, Centranthus ruber will begin to flower in late spring or early summer - in southeastern Michigan it usually begins to flower in early June. Given regular deadheading, flowering will continue until fall.
Close-up of a flower cluster

Light Requirements: Centranthus ruber needs full sun.
Soil Requirements: This plant will grow in most normal soils but needs moderately good drainage. It is also very tolerant of alkaline soil conditions, which is one of the reasons why it grows well even in the cracks of the mortar of old walls.
Centranthus ruber in the front border of my family's Michigan home early in the season

Siting in the Garden: Centranthus ruber needs a sunny spot with decent drainage but is otherwise quite adaptable and can be planted in perennial borders, informal, naturalized plantings, rockeries, and even in the cracks of stone walls.
Care: A good amount of compost or organic fertilizer such as bone meal incorporated into the soil at the time of planting does the plant well, as do occasional top dressings of compost and a good layer of leaf mulch later on. However, none of these treatments are absolutely necessary and they are obviously impossible if the plant is being grown between rocks or on a wall. During extended periods of drought Centranthus ruber might need to be watered but otherwise the main care the plant needs is bi-weekly deadheading during the summer months. This keeps the plants tidy and flowering continuously.
Propagation: Centranthus ruber is easily grown from seeds which are formed in abundance if one stops removing spent flower clusters. The seeds have little parachutes like the seeds of dandelion (Taraxacum officinale) and if the formation of seeds is allowed the plants will often self-seed. However, seedlings tend to appear in moderate number and relatively close to the mother plant so that the species usually does not spread aggressively. If self-seeding is not wanted but you still want to grow additional specimens of the plant, harvest the seeds as soon as their little parachutes start unfolding. This does not happen to all the seeds on a cluster simultaneously, so you might have to collect the seeds over the course of several days. In spring the seeds may be started in doors in a bright window and the seedlings planted in the garden once temperatures warm up or they may be sown directly in the garden in late spring. Division is not advisable as a method of propagation for this plant since it tends to form a woody base that cannot be split without harming or even killing the plant.
Centranthus ruber in my parents' frontyard once again
Use in the Garden: Colorful, tough, and adaptable, Centranthus ruber can be used in many ways in the garden. It makes a great choice for the middle level of perennial borders and mixed beds but also looks beautiful billowing over the edge of a path or retaining wall. It is also suitable for informal and naturalized plantings, rockeries and gravel gardens and can even be made to colonize stone walls and cracks in paved or tiled areas.
Sources: http://davesgarden.com/guides/pf/go/136/
http://plants.usda.gov/java/profile?symbol=CERU2
http://www.plant-identification.co.uk/skye/valerianaceae/centranthus-ruber.htm




2 comments:

  1. A pretty flowering plant. I wonder if it can grow in the tropical region?

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  2. I have no experience growing it in a tropical climate but I did read that it is grown and has even become naturalized in Hawaii so I think it might be worth a try. It definitely holds up very well to heat and intense sun, so I would guess the main issue in a wet tropical climate would be good drainage.

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