by Mark N. McCann
Since its introduction to Oregon from its native Ireland, prior to the turn of the century, gorse (Ulex europaeus) has proven to be resilient, prolific and pernicious, as anyone caught in the unforgiving spines of this primarily coastal invasive can attest. Brought to this continent as an ornamental, one can only wonder if the Marquis De Sade might have suggested this tortuous greenery. Scotland, long known for the patches of gorse bounding the rough of its “links” golf courses, shows one more reason to aggressively eliminate this non-native pest.
In the 1950’s gorse was estimated to cover 25,000 acres of Oregon’s high rent coastal properties, but the elevation of the coastal range has, to date, kept the bulk of the invader out of the interior valleys of the Northwest. The plant’s dependence on temperate climes without the extremes of heat or cold, including frigid winds, and an intolerance of drought conditions, keeps gorse along a narrow band from Santa Cruz, California northward.
Disturbed or infertile sites provide an excellent nursery—as well as for most weedy species—while the reduced competition from native plants allows the invaders free reign. Then gorse requires only high rainfall and reasonable drainage, making the stabilized sand dunes of the western coast ideal habitat for it. A secondary danger of this species is its highly flammable foliage, thus multiplying the hazards of the large, single-species stand gorse will create if left unchecked. Coupled with the windy nature of the coastal environment, gorse plays the lead in an insurance adjuster’s nightmare.
Gorse is similar in color and basic appearance to Scotch broom (Cylisus scoparius) until examined more closely. Both deciduous species reach heights up to three meters, have yellow flowers and bear fruit in flattened pea-like pods. But the spines of the gorse will give an unsuspecting gardener a painful identification key that will be long remembered. Seeds are usually not formed on gorse prior to the second season of growth, but the small seeds are hard and water-impermeable, contributing to a dormancy of up to 30 years! Any species with a seed that resilient requires special precautions for complete removal. In some instances chickens have been used to police up stray seeds from an area after removal of the foliage.
As with all legumes, gorse is a nitrogen fixer—in and of itself not a bad thing—but it also raises acidity in the nearby soil. One of the most often used methods for removal of gorse, proscribed burning, can actually inhibit other species’ regrowth by reducing the available nitrogen in the soil. This can allow gorse to come back with a vengeance, as seeds are heat tolerant and gorse is a pioneer species fixing nitrogen from the air.
The prickly nature of gorse makes the “tug and lug” method Herculean. Many prefer to cut the plant off at the ground and deal with the root after the fact. Cutting gorse off before it flowers will reduce the number of seeds and will deplete the plants stored energy base. Moderate success has been achieved with yearly cutting, though it might require three years or more to finally drain the reserves the main roots could hold.
While the plants are young, less than a couple of years, the mat-like form of it can be hoed easily before the thorns grow on the stems. This is the best time to eliminate gorse, but often it goes unnoticed until it becomes a pure stand.
Removal of the seed base may be the most difficult matter with gorse. Small size and longevity will prove difficult to overcome. As mentioned before, chickens have been used to eat the seeds, and quail have been known to delight in seed dining also.
As always, the avowed policy of the Rainy Side Gardener.com is to encourage alternatives to herbicide, but with gorse the number of effective agents is limited, even among persistent chemicals.
An integrated plan is most effective, using mechanical means to remove the plant prior to flowering, eliminating seed base, and increasing shade and competition through extensive replanting with natives that can shade out all invasive species. Deep shade will quell gorse. Fortunately, there are numerous natives that thrive on the coast and provide deep shade.
Using native plants that contain allelopathic qualities can help reduce the number of weeds within an area. For deep shade, plant evergreen huckleberry (Vaccinium ovatum), salal (Gaultheria shallon), or Sitka spruce (Picea sitchensis). For an allelopathic native, try the salmonberry (Rubus spectabilis).
There are many plants to use on the coast if a gardener needs to create a barrier on a property. Salal and evergreen huckleberry are cheap and found in many coastal nurseries. Both create an impenetrable barrier. California wax myrtle (Myrica californica) will make an effective hedge and can grow to six meters if untrimmed. A coastal gardener may opt for one of the many northwest natives that will retain their leaves throughout the wet but mild winters.
Wildlife along the coast is abundant locally, and any of the berry producing species endemic to the coast will provide both cover and food throughout the winter. Snowberry (Symphoricarpos albus) is often planted to provide forage. Though the waxy snowberry fruit is not preferred food, the long lasting berries can get local fauna through most any period where regular dietary options might be in less abundant supply.
Mark N. McCann is currently working on a book about Green Space and Stream Stewardship within the Vancouver-Seattle-Portland-Eugene (VSPE) Corridor. Based on his five years of experience removing invasive species, and replanting and propagating natives species within the Tryon Creek State Natural Area (TCSNA) as a member of the Adopt-A-Plot program. He has been a Citizen Member of the Tryon Creek Watershed Council, Friends of Tryon Creek and presently is a volunteer at Berry Botanic Garden, specifically in the Native Plant’s Trail and in the Propagation Department.
Photo courtesy of G.A. Cooper @ USDA-NRCS PLANTS Database.