Swamp Cottonwood – Populus heterophylla

Swamp Cottonwood
Family Salicaceae
Height: to 80' Spread: 40-50'
Form: Upright /  Hardy to USDA Zone 3

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Swamp Cottonwood Foliage
Populus heterophylla

Swamp cottonwood is of secondary importance among bottom-land hardwoods. The species, sometimes referred to as black cottonwood, river cottonwood, downy poplar, or swamp poplar, may grow on sites that are too wet for other native poplars. It is a difficult species to grow from cuttings, a characteristic that limits its commercial value. Swamp cottonwood inhabits the wet bottom lands and sloughs of the Coastal Plain from Connecticut and southeastern New York to Georgia and northwestern Florida, west to Louisiana. It grows north in the Mississippi Valley to southeastern Missouri, western Tennessee, Kentucky, southern Illinois, Indiana, Ohio, and southern Michigan [1].

Swamp Cottonwood
16 year old swamp cottonwood

Though most often found on heavy clays, swamp cottonwood also grows on the edges of, but not in, the muck swamps of the Southeast. Optimum growth and development is in the deep, moist soils of shallow swamps and low-lying areas near tidewater.

Sites that are too wet for eastern cottonwood (Populus deltoides) will support swamp cottonwood. Examples are shallow swamps, sloughs, and very wet river bottoms where the water table remains near the soil surface for all but 2 or 3 months in the summer and early fall. In the southern part of its range, low, wet flats provide the driest sites occupied by swamp cottonwood. However, in southern Illinois it is a dominant or codominant tree on soils with available moisture varying from 3 to 21 percent for the 61- to 76-cm (24- to 30-in) layer.Swamp cottonwood grows naturally on at least eight major soil types common to the Midsouth: Alligator, Amagon, Arkabutla, Forestdale, Perry, Rosebloom, Sharkey, and Tensas. The soils represent several families and the orders Alfisols, Inceptisols, and Entisols. They range from 4.6 to 5.9 in pH and from 24 to 65 percent clay in the surface 0.3 m (1 ft).

Flowering and Fruiting- Swamp cottonwood is dioecious. Flowers are proteranthous, appearing from March to May. Staminate catkins are rather stiffly pendant, oblong, cylindric, and 5 to 10 cm 2 to 4 in) long; pistillate catkins are 5 to 15 cm (2 to 6 in) long, pendulous, slender, and raceme-like. Pollination is by wind. Fruits ripen and the seeds fall from April through July.

Seed Production and Dissemination- Trees start seed production at about 10 years. Reddish-brown obovoid seeds number about 330,700/kg (150,000/lb) (9). Seeds are very small, light in weight, and tufted with hairs, features that allow them to be blown over 100 in (330 ft) by wind and to float for a considerable distance in water. Water is an important transporting agent since the bottom lands normally flood during the seedfall period. Numerous seeds are produced annually, but under natural. field conditions they remain viable for no more than a week or two.

Seedling Development- Germination is epigeal. Best seedling establishment is from seeds that quickly settle on unshaded, moist mineral soil in shallow swamps, deep sloughs, and along often-flooded creeks or rivers. Seedlings require nearly full sunlight to survive and grow. They also need an abundance of moisture, especially during the early part of the growing season. Seedlings usually occur in groups but seldom cover a large area [1].

Swamp Cottonwood Bark
Swamp Cottonwood Bark

Vegetative Reproduction– Cuttings from juvenile plants will root but probably not as well as those of eastern cottonwood (4). Stumps less than 30 cm (12 in) in diameter are likely to produce sprouts.

Damaging Agents- There are no reported insect or disease problems associated specifically with swamp cottonwood. But the ones that attack eastern cottonwood probably also damage swamp cottonwood. Important insect enemies include the cottonwood leaf beetle (Chrysomela scripta), cottonwood twig borer (Gypsonoma haimbachiana), poplar borer (Saperda calcarata), and the cottonwood borer (Plectrodera scalator). Among the more important diseases are Melampsora leaf rust (Melampsora medusae) and a number of canker diseases, including Septoria, Cytospora, and Fusarium.

Special Uses – There is no market specifically for the small volume of swamp cottonwood harvested. The wood resembles that of eastern cottonwood and is generally sold as such. Among the uses for cottonwood lumber and veneer are boxes, crates, and interior parts for furniture. Pulpwood is used in high-grade book and magazine paper. To date, few other uses have been found for the species. It is rarely cultivated for ornament, does not produce important wildlife food, and is important to flood or erosion control only in very small, localized areas. Instead of swamp cottonwood, a closely related species, eastern cottonwood, is chosen for planting because it outperforms swamp cottonwood on all except the wettest sites. —USDA Forest Service Fact Sheet

1. USDA Forest Service fact sheet,"Swamp Cottonwood"
2. NATIONAL AUDUBON SOCIETY, National Audubon Society Field Guide to North American Trees
Family Salicaceae — Willow, Cottonwood, Aspen
There are only two genera in this family, Salix (willows), with about 300 species, and Populus (poplars), with barely 40 species. Salicaceae are found throughout the temperate parts of the world, with the majority of species occurring in the north; both willows and poplars have a strong affinity for water.
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