Identification & Description:
The tallest native cottonwood, with open crown of erect branches and sticky, resinous buds with balsam odor. Leaves 3-6 in (7.5-15 cm) long, 2-4 in (5-10 cm) wide. Height: 60-120 ft (18-37 m). Diameter: 1-3 ft (0.3-0.9 m), sometimes much larger.
As you cross the continental divide towards British Columbia, or head south towards the Crowsnest Pass and the U.S. Rockies, the balsam poplar slowly gives way to the black cottonwood. Technically, the cottonwood is considered a subspecies of balsam poplar, and like its relative, it prefers low lying moist habitats, often along river courses. It is the largest of the poplar species in the Rockies, often reaching heights of 40 m (130 ft).
Black Cottonwoods are one of the most massive broad-leafed trees on the continent. The large leaves are egg-shaped, almost as wide as they are long, and rapidly taper to a point. They range in size from 7-13 cm (3-5 in), and are dark green above, and silvery-green below. Like the balsam poplar, they also exhibit brown resin blotches on the lower surface. The bark on young trees is a yellowish-green colour, becoming gray and furrowed on older trees. It is the most important deciduous tree in B.C., and is heavily logged.
A decidious tree growing to 40m by 12m at a fast rate. It is hardy to zone 5. It is in flower from April to May, and the seeds ripen from May to June. The scented flowers are dioecious (individual flowers are either male or female, but only one sex is to be found on any one plant so both male and female plants must be grown if seed is required) and are pollinated by Wind. The plant not is self-fertile. We rate it 2 out of 5 for usefulness.
The plant prefers light (sandy), medium (loamy) and heavy (clay) soils, requires well-drained soil and can grow in heavy clay soil. The plant prefers acid, neutral and basic (alkaline) soils and can grow in very acid soil. It cannot grow in the shade. It requires moist soil.
• Hardy, straight trunked
• Fast growing if have ample moisture and plenty of nutrients
• Of all BC’s broad leafed trees the balsam poplar if the tallest
• Has a resinous fragrance from the sticky buds
• Bees use this sticky resin from the buds as a caulking material in their hives
• A chemical produced in young twigs deters snowshoe hare from feeding on them
Leaf: Alternate, simple, deciduous; variable in size and shape on same tree, commonly 3 to 6 inches long, but can be much larger; ovate-lanceolate to deltoid, dark green above and silvery white below with rusty smears of resin, margins wavy to crenate; petiole long, and most often round but may be flattened.
Flower: Dioecious; borne in long, drooping aments that appear before the leaves.
Fruit: Rounded, 3-valved capsules (1/4 to 1/2 inch in diameter) which open to release many cottony-tufted seeds; seeds are very tiny and black.
Twig: Moderately stout, greenish brown to olive-gray, often ribbed or angled in cross section when young, covered with distinct lenticles, spur shoots are common on older branches; buds are long (1/2 to 3/4 inch) and sharp-pointed, resinous and aromatic, covered with imbricate scales. Twig has a bitter aspirin taste.
Bark: When young it is smooth and yellowish tan to gray; later gray to gray-brown and broken into deep furrows and flattened ridges, up to 2 1/2 inches thick.
Form: The tallest broad-leaved tree in the West, growing to 200 feet tall and 6 feet in diameter. Has a broad, open crown.
Southern Alaska south to southern California and east in mountains to extreme southwestern Alberta and Montana; also local in southwestern North Dakota and northern Baja California.
Flowers; Inner bark; Sap.
Inner bark – raw or dried. It is usually ground into a powder and used as a flour, this is normally mixed with other flours for making bread etc. It is best used in the spring. The inner bark is mucilaginous and extremely sweet, but it sours or ferments rapidly and so, unlike most inner barks, it cannot be dried for winter use, though it can be sun-dried for more immediate use.
Catkins – raw or cooked. A bitter flavour.
Sap – used for food.
• Modern – tissues, other paper products, resin covered buds often collected for their scent, the resin from the buds is used for natural health ointments
• Traditional – cottonwood: wood – canoes, sideboards for riding, cradles, firewood (the ashes were used to make a cleanser for hair and buckskin, masks; roots – rope; inner bark – soap, food; resin – adhesive
• Cottonwood and balsam buds – resin from buds used to treat sore throat , coughs etc, a balm was also made from cottonwood buds to relieve congestion
• Balsam poplar: bark – boiled as a poultice for wounds, worm medicine; inner bark – food Adhesive; Basketry; Containers; Cork; Dye; Fuel; Insulation; Paint; Rooting hormone; Scourer; Soap; Soap making; String; Stuffing; Waterproofing; Wood.
An extract of the shoots can be used as a rooting hormone for all types of cuttings. It is extracted by soaking the chopped up shoots in cold water for a day.
A yellow dye is obtained from the leaf buds.
The bark of large trees is thick and corky. It is made into containers for carrying and storing food, also as a lining for underground food stores.
The inner bark has been shredded, spun together with red or yellow cedar inner bark (Thuja plicata, Juniperus spp and Chamaecyparis nootkatensis) and used as a twine.
A glue is made from the aromatic gum on the spring buds. Very strong, it can also be used as a waterproofing for wood etc. When mixed with pigment it can be used as a paint.
A string is made from the roots.
The supple young branches have been used as lashings or tying thongs.
The seed fluff is used as a stuffing material for pillows etc.
The wood ashes are a soap substitute, they can also be mixed with oil to make a soap.
The white inner bark is also a soap substitute, it can be dried and stored for later use. The inner bark has also been used as a scouring pad.
The roots have been used for making baskets.
Wood – soft, moderately strong, easily worked, rather woolly in texture, without smell or taste, of low flammability, not durable, very resistant to abrasion. Used in making crates, packing material the staves of barrels, woodenware and for pulp. It makes an excellent fuel.
Populations of black cottonwood grow in climates varying from relatively and to humid, but best growth is attained in the humid coastal forests of the Pacific Northwest. Annual precipitation ranges from 250 min (10 in) to more than 3050 min (120 in). Only about one-third of the annual precipitation occurs during the growing season, and in mountainous and inland areas much of the dormant-season precipitation falls as snow. The frost-free period ranges from about 70 days in the interior areas to more than 260 days in southern California. Maximum temperatures range from 16° to 47° C (60° to 117° F); minimum temperatures, from 0° to –47° C (32° to –53° F).
Soils and Topography
Black cottonwood grows on a variety of soils and sites, from moist silts, sands, and gravels of islands and new river bars to rich humus soils, loams, and occasionally clay soils of upland sites . The most extensive black cottonwood stands are on soils of the order Entisols; the species also is common on Inceptisols and occasionally may be present on soils of other orders. High soil acidity (low pH) may restrict occurrence of black cottonwood on fine-textured soils where other site factors are favorable. Studies in British Columbia have indicated that abundant moisture, nutrients, oxygen, and nearly neutral soil reaction (pH 6.0 to 7.0) are required for optimum production. Growth is best at low elevations on deep, moist alluvial soils, but some upland soils are productive cottonwood sites. The latter include loessial soils of high nutrient status in areas of abundant rainfall.
Black cottonwood grows from sea level to 600 in (2,000 ft) on the Kenai Peninsula of Alaska and up to 1500 in (5,000 ft) in the Cascade Range of Washington. In British Columbia, the elevation range extends to nearly 2100 m (7,000 ft) in the interior valleys of the Selkirk Range. In central and eastern Washington, as well as other dry areas, the species is usually limited to protected valleys and canyon bottoms, along stream banks and edges of ponds and meadows, and to moist toe slopes.
A very easily grown plant, it does well in a heavy cold damp soil. Prefers a deep rich well-drained circumneutral soil, growing best in the south and east of Britain. Growth is much less on wet soils, on poor acid soils and on thin dry soils but this species is more tolerant of acid soils than other members of the genus. It dislikes shade and is intolerant of root or branch competition. Plants are reasonably wind resistant, but they do not grow well in exposed upland sites.
Many forms of this species are susceptible to bacterial canker, the female clone ‘Fritzi Pauley’ is resistant.
A very fast growing and ornamental tree, it does well in western Britain where trees have reached 25 metres tall in 20 years.
The leaf buds, as they swell in the spring, and the young leaves have a pleasing fragrance of balsam. The fragrance is especially pronounced as the leaves unfold.
Poplars have very extensive and aggressive root systems that can invade and damage drainage systems. Especially when grown on clay soils, they should not be planted within 12 metres of buildings since the root system can damage the building’s foundations by drying out the soil.
Dioecious. Male and female plants must be grown if seed is required.