RHAMNUS PURSHIANA: Cascara
Our native of the Buckthorn family, Rhamnus purshiana, is a real “sleeper” among our native trees -- frequently overlooked and underappreciated -- yet it is a widely-adaptable small tree that is a favorite for birds and suitable for the smaller urban garden; growing as a shrub to about 15’, it can also reach 30’ as a small tree.
Described once as looking like “an alder crossed with a birch with a cherry thrown in” -- the Cascara’s mottled gray bark is topped with deeply-ridged, oval leaves usually dark green on their topside with lighter green underneath.
Depending on the amount of sun it’s grown in, the fall color can range from yellow to orange - red in the fall. The flowers are small, creamy greenish-white, generally hiding amongst the foliage in small clusters. Butterflies like them, however, and will seek them out. The fruit that follows are small, purple-black beads that attract many species of birds.
Cascara grows in a wide variety of conditions – wet to dry, sun to shade – though it will perform best in a partly sunny, moist site with well-drained soil. That being said, it will happily take summer dry conditions, making it an appropriate site for seasonally wet areas like a rain garden.
Although aphids can sometimes be a pest of Cascara, and its foliage has been noted to be susceptible to Phytophthora, it seems that it tends to be mostly problem-free; and all of its virtues of adaptability, seasons of beauty and attractiveness to birds far outweigh the risks.
Common name: Cascara, Cascara Buckthorn
Native Range: British Columbia south to California, primarily west of the Cascades
Characteristics: Grows as a tall shrub to small tree, 15-30’. Gray bark; oval, large ribbed leaves that are dark green when they emerge, turning yellow to orange-red in fall; small, greenish-yellow flowers followed by purplish-black fruit much loved by birds.
Culture: Takes sun or shade, preferring a mix of both. Prefers moist to wet, well-draining soil; but is also tolerant of summer-dry conditions.
Pests/Diseases: Aphids are sometimes a problem; does not thrive as vigorously in areas of high-pollution. In general, however, Cascara is fairly problem-free.