Plant Profiles Rhododendron Rhododendron Ponticum

Rhododendron ponitcum is a species of evergreen Rhododendron known for its light purple to lavender flowers. The species is found in two distinct regions of Europe and Asia Minor, where it is classified as two different subspecies. Rhododendron ponticum subspecies ponticum is native to Turkey, Lebanon, Caucasus and Bulgaria, while Rhododendron ponticum subspecies baeticum is found in the southern regions of Spain and Portugal.

Similar in appearance to other species and hybrids of Rhododendron, Rhododendron ponticum has dark olive green leaves of 4-6 inches in length that are leathery and retained throughout the winter. The bark is grayish brown and becomes flakey and peals off on older specimens. Blooms are produced in mid to late spring (May-June). The flowers are generally a medium purple but can range from white to light lavender to dark purple. After pollination by bees and other insects, seed capsules form and grow during the summer and then mature in the fall. Although considered a shrub, Rhododendron ponticum may become a small tree and is able to reach heights of 10-15 feet tall and wide. This species is highly adaptable and can tolerate very sandy acidic soils and full sun exposure as long as the soil is kept fairly moist at all times.

This species has lent its genetics to many different Rhododendron crosses resulting in some of the most beloved hybrids of Rhododendrons around the world. There is even a variegated version of the species, known simply as Ponticum Variegatum, that sports thin white margins along each leaf edge. Rhododendron ponticum is also used as graft stock for other hybrids that are less hardy or do not tolerate a wide range of growing conditions.

Although it is an important species to Rhododendron breeders and horticulturists alike, Rhododendron ponticum, unfortunately, has also proven to be highly invasive in areas where it was intentionally introduced as a garden ornamental. Unlike other species of Rhododendron, Rhododendron ponticum has the ability to form roots on branches that are touching if not somewhat buried in the ground. This ability allows the plants to spread out a greater distance much more quickly. Germination of seed also accounts to the spread of these plants. Rhododendron ponticum produces 3,000 t0 7,000 tiny seeds per flower which are dispersed by wind after the seed capsules dry and split in the fall. The high number of seed dispersion coupled with the ability to clone itself gives Rhododendron ponticum a competitive edge, allowing it to survive and reproduce in one form or another.

Rhododendron ponticum was introduced into United Kingdom during the 18th century as an ornamental garden plant. Since its introduction, it has spread across England, Scotland and Ireland to all corners and edges in a very short amount of time. It has also been introduced into New Zealand and North America where it is also quickly becoming an invasive species.  Aside from its ability to clone itself, Rhododendron ponticum has the ability to choke out the competition with its dense foliage and toxic leaves that fall to the ground underneath the plants. The dead toxic leaves release compounds into the soil to prevent any other type of plant from attempting to germinate while the dense canopy keeps little light from entering the forest floor.

Control of this plant is possible, but takes diligence and work. The best method of prevention is to pull up young plants at sight.  This species takes 10-12 years to mature for successful flower production, so the sooner it is removed, the better. Larger specimens, especially those that were allowed to naturalize in an area unadulterated for years, will need a much more aggressive approach to their eradication. A method of chopping up and digging up all plant material is needed to fully remove all parts of the plant that may potentially try to resprout.  After the mature plant material has been removed, the ground beneath the plants will be uninhabitable after so many years of the toxic leaf accumulation creating a dead zone for any other plant life. Once the plants have been permanently removed, native plants may slowly reclaim the soil as the levels of toxic compounds dissipate.

Rhododendron ponticum is a beautiful species of Rhododendron that, like many other species around the world, has many good and bad qualities. This is most apparent when it is taken from its native habitat and introduced into a different one.