What hardiness zones is Frangula purshiana suitable for?

Frangula purshiana is suitable for USDA hardiness zones 5, 6, 7, 8, 9.

What are the sun requirements for Frangula purshiana?

Frangula purshiana requires Part Shade.

How much water does Frangula purshiana need?

Frangula purshiana has Low water needs.

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Broadleaf Deciduous Trees

Frangula purshiana

cascara

Rhamnaceae

British Columbia south through Washington, Oregon, California; east to Idaho and Montana; moist to mesic forests, streambanks, and forest margins

At a Glance

TypeTree

HabitUpright

FoliageDeciduous

Height15-40 feet (4.5-12 m)

Width10-20 feet (3-6 m)

Maturity15 years

Growing Zones

USDA Hardiness Zones

5 - 9

Zone 5

Zone 6

Zone 7

Zone 8

Zone 9

These zones indicate the coldest temperatures this plant can typically survive.

Frost Tolerancehardy

Key Features

Attracts Pollinators

Drought Tolerant

Native to North America

Maintenancevery low

Overview

A small to medium-sized deciduous tree in the family Rhamnaceae, native to moist to mesic forests, streambanks, and forest margins from British Columbia south through Washington and Oregon to California, and east to Idaho and Montana. Formerly classified as Rhamnus purshiana; Frangula purshiana is the current POWO-accepted name. One of the most significant medicinal plants of the Pacific Northwest — the bark (commercially known as 'cascara sagrada') contains anthraquinone glycosides with powerful cathartic properties and was used medicinally by many Indigenous peoples of the Pacific Northwest for centuries; it was the most widely prescribed laxative in North America through much of the 20th century. Trees grow 15–40 feet (4.5–12 m) tall, typically as a single-trunked tree or large multi-stemmed shrub with thin, smooth, grayish bark that develops shallow fissures with age. Leaves are broadly oval to elliptic, 2–6 inches (5–15 cm) long, with 10–15 pairs of prominent, straight, parallel secondary veins running from midrib to margin — the most immediately diagnostic leaf character. Small clusters of inconspicuous greenish-yellow flowers in May–June attract native bees. Berries ripen from green to red to purplish-black July–September, providing important food for over 20 bird species. The bark and unripe berries are toxic to humans and pets.

Native Range

Native to moist to mesic forests, streambanks, and forest margins from British Columbia south through Washington and Oregon to California, and east to Idaho and Montana, growing in a wide range of acidic to neutral soils.

Suggested Uses

Planted as a native woodland tree, riparian buffer, or bird-habitat shrub at 10–15 foot (3–4.5 m) spacing. An excellent medium-sized native tree for Pacific Northwest woodland and forest garden designs — shade-tolerant, undemanding, and providing exceptional wildlife value. The berries (July–September) attract over 20 bird species. Historically one of the most important medicinal plants of the Pacific Northwest — the bark was commercially harvested as cascara sagrada laxative. Of significant educational interest for Indigenous plant use, botanical history, and Pacific Northwest ecology courses.

How to Identify

Identified by broadly oval to elliptic leaves 2–6 inches (5–15 cm) long with 10–15 pairs of prominent, straight, parallel secondary veins running directly from midrib to leaf margin — the parallel venation pattern is the single most reliable identification feature and immediately distinguishes cascara from other PNW forest trees. Thin, smooth, grayish bark with shallow fissures that becomes darker and more furrowed with age. Small clusters of inconspicuous greenish-yellow five-petaled flowers appear May–June. Berries ripen from green to red to purplish-black (July–September) — the progression from red to black on the same cluster is characteristic. The straight parallel venation, smooth grayish bark, and small red-to-black berries are collectively diagnostic.

Appearance

Size & Dimensions

Height15' - 40'

Width/Spread10' - 20'

Reaches mature size in approximately 15 years

Colors

Flower Colors

green

yellow

Foliage Colors

green

Fall Foliage Colors

yellow

orange

purple

Bloom Information

Bloom Period

~4 weeks

Spring

Blooms May through June with small clusters of inconspicuous greenish-yellow five-petaled flowers 0.1–0.2 inch (3–5 mm) across in leaf axils — not showy but important for native bees and other insects. Berries ripen from green to bright red to purplish-black July through September — the transition of colors on the same cluster is ornamentally interesting and provides food for over 20 bird species including cedar waxwings, thrushes, and band-tailed pigeons.

Detailed Descriptions

Flower Description

greenish-yellow; small inconspicuous five-petaled flower clusters in leaf axils; May–June; followed July–Sept by berries ripening green to red to purplish-black — progression of colors on same cluster characteristic

Foliage Description

medium green; broadly oval to elliptic 2–6 inches with 10–15 pairs of prominent, straight, parallel secondary veins running midrib to margin — most diagnostic feature; yellow-green fall color

Growing Conditions

Sun Requirements

Full Sun

Partial Shade

Full Shade

Tolerates up to 8 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.0 - 7.5(Neutral)

357912

Soil Types

loamclaysand

Drainage

well drained

Water & Climate

Water Needs

Low

Frost Tolerance

hardy

Time to Maturity

10-15 years

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Plant in full sun to full shade in moist to average, acidic to neutral soil with a pH of 5.0–7.5. One of the most shade-tolerant native trees of the Pacific Northwest — grows naturally in deep forest understory. Adaptable to a wide range of soil moisture conditions from moist streambank soils to average well-drained forest soils. Minimal care required once established. Drought-tolerant once established in average soils. No fertilizer needed. Do not consume bark or unripe berries — toxic.

Pruning

Minimal pruning required. Remove dead or crossing branches in late winter. Can be trained to a single trunk or maintained as a multi-stemmed large shrub. Generally requires no regular pruning to maintain health and form.

Pruning Schedule

early spring

Maintenance Level

very low

⚠️ Toxicity Warning

Toxic to pets and humans