Rhamnus purshiana Seeds | Cascara Sagrada
LATIN NAME: Rhamnus purshiana
COMMON NAME: Cascara Sagrada
Plant Profile
Cascara sagrada is a small deciduous tree of the Pacific Northwest, growing six to fifteen metres in the understory of Douglas fir and hemlock forest from British Columbia to northern California. It has a slender, often leaning trunk with grey bark, oval leaves with finely toothed edges and prominent veins, and clusters of small greenish flowers in spring. The fruit is a small, round berry that turns from red to purple-black and is eaten by birds. The bark is thin, silvery and slightly bitter, and it was the most widely used laxative in North America for a century. The tree suckers from the root and spreads into thickets in disturbed shade, and it is common along forest roads and streams.
Science & Biotechnology
The active compounds are cascarosides, anthraquinone glycosides that pass through the small intestine unchanged and are activated by bacteria in the colon, where they stimulate motility and secretion. Fresh bark contains reduced anthrones that cause violent cramping and vomiting, so it must be aged for at least a year before use, a piece of traditional knowledge that turned out to be chemically exact. Cascara was an official drug in the United States Pharmacopoeia and a standard over-the-counter laxative until 2002, when the FDA reclassified stimulant laxatives as not generally recognised as safe because of inadequate long-term data. It remains in European monographs for short-term use. Chronic use causes potassium loss and dependence, and the bark is now regulated in several countries.
Uses & Benefits
The aged bark is the only part used, and it appears in teas, tablets and tinctures for short-term constipation. It is a strong herb, not a daily one, and it should not be taken by anyone with intestinal inflammation or during pregnancy. The wood is light and soft and has little commercial value, and the berries are not edible, though birds take them freely. In the garden the tree is useful for shade, for a wildlife border and for its autumn colour, which is a soft yellow. It is one of the few small trees that will grow in dry shade under conifers, and it tolerates heavy pruning. Its flowers are a good early nectar source for native bees, and its thickets give cover for small birds.
Growing from Seed
Clean the pulp from the berries and stratify the seed in damp sand at four degrees for three months. Sow in spring, one centimetre deep, in a leafy, free-draining mix, and keep in half shade. Germination takes four to eight weeks and is often uneven. The seedlings grow slowly at first and need shade for their first summer. Pot on once, then plant out in autumn into moist, well-drained soil in half shade or full sun. Water for the first two summers and keep a leaf-mould mulch over the roots. The tree suckers once established, so site it where a thicket is acceptable. Prune in winter if a single stem is wanted.
Our Take
A modest understory tree with a powerful bark and a caution attached. Grow it for the birds and the shade, not the medicine cabinet.
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