Marin IJ Articles

Marin's rhododendrons less traveled, and why they may make all the difference

• Terry Amerson

• 

  The Pacific Rhododendron, Rhododendron macrophyllum sharing its large clusters of blooms. Photo: John Rusk

  Robert Frost's famous poem "The Road Not Taken" seems to anticipate the dilemma many Marin gardeners face when looking for that perfect ornamental plant. We may have long admired a beautiful rhododendron growing nearby, and we may happen to have the perfect site to plant our own. Searching online and in garden centers, we discover dozens of commercially available rhododendron cultivars created from the over 1200 species found worldwide. In fact, thousands of cultivars have been created from this global gene pool, making rhododendrons among the most cosmopolitan of plants. The selection is almost overwhelming. At this moment, some gardeners may pause, having learned that three species of rhododendrons are actually native to Marin that will better support our vibrant, diverse, and extremely delicate ecological systems.

  So, we are at that fork in the road. Do we plant the easily obtained commercial cultivar with impressive genetic lineages spanning continents and oceans? Or do we take the less conventional path by planting one of our three equally beautiful but far less traveled native rhododendrons?

  

  The Western Labrador Tea, Rhododendron columbianum is an old favorite and a recent addition to Marin’s native rhododendron family. Photo: David Hofman

  The largest of our natives is the Pacific Rhododendron. Its Latin name, Rhododendron macrophyllum, literally means "Ros" Tree with Big Leaves." An "evergreen species, it can attain a height of fifteen feet. Blooming from March through May, its showy clusters of flowers, known as trusses, balance well with its large, thick, glossy leaves. Flower colors range from shades of white to pink and lavender. It is naturally found along the coastal conifer forest margins and Mount Tamalpais's shaded slopes. When in flower, this magnificent native is spectacular. Hikers coming upon the Pacific Rhododendron in bloom are always happy about the path they have taken.

  The Western Labrador Tea is known for its spicy, aromatic scent and racemes of small white and creamy yellow flowers. Native Americans have used the leaves of this culturally significant native to make tea, hence its common name. Formerly known as Ledum glandulosum, it has been reclassified and is now officially named Rhododendron columbianum. It is a very low-growing evergreen shrub generously blooming from May through August. This unique plant is commonly found along moist shoreline habitats.

  

  The Western Azalea, Rhododendron occidentale with its distinctive funnel-shaped flowers and prominent stamens. Photo: Eric Hunt

  The Western Azalea is known botanically as Rhododendron occidentale. It is a low-growing deciduous shrub that grows between four and eight feet in height. Autumnal foliage of some varieties may turn a stunning crimson before dropping. Widely praised for its fragrance, it will display showy trusses of flowers in May and June. Long decorative styles and stamens accent each beautiful funnel-shaped bloom. Flower colors range from white to pink or lavender and may display yellow or orange smudges, which attract pollinators. The Western Azalea is often found in lower riparian settings, where coastal fog supplies additional moisture.

  Our natives are understory plants with shallow fibrous roots that won't require deep holes but will need well-drained, slightly acidic soil that can be kept uniformly moist. They will prefer dappled morning light and shade from the hot afternoon sun. Because they are Marin natives, they have evolved and adapted to hot, dry summers and cool, wet winters. And because they are natives that have evolved in our soils, they won't require the same intensive chemicals and fertilizers as many cultivars. They are happy here.

  Marin's rhododendrons will have a more direct and positive impact on our natural communities than cultivars precisely because they have evolved within our complex ecosystem. The evolutionary symbiosis with soil microorganisms and pollinators, including butterflies, bees, and birds, cannot be overstated. Commercial cultivars are certainly appealing because of the vibrant rainbow of colors and forms offered, but they cannot begin to approach the ecological value of our beautiful native rhododendrons.

  And that may make all the difference.