# Swamp Cottonwood (Populus heterophylla)

> A big poplar for swamps and sloughs, with heart-shaped leaves up to 8 inches long that open in white down, rare at the north end of its range.

Also called swamp poplar, downy poplar, river cottonwood, Populus argentea. Category: Uncommon Yard Trees. Grown from seed by Blue Whale Trees. Web version: https://bluewhaletrees.com/plants/swamp-cottonwood/

![Swamp cottonwood (Populus heterophylla) open seed capsules spilling white cotton on a catkin](https://bluewhaletrees.com/img/plants/swamp-cottonwood-h1610-800.jpg)
*Photo: Kristine Paulus, CC BY 2.0 · [Wikimedia Commons](https://commons.wikimedia.org/wiki/File%3APopulus_heterophylla_seeds.jpg)*

## Facts

- Type: Large tree
- Mature height: 70 to 90 ft
- USDA hardiness zones: 6 to 9
- Grows wild in: Floodplain forests, stream banks, swamps and wet flats
- Native range: 24 states, north to Michigan, south to Florida and west to Missouri (Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, Indiana, Kentucky, Louisiana, Maryland, Massachusetts, Michigan, Mississippi, Missouri, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee and Virginia)
- Sun: Full
- Soil moisture: Wet, Average
- Growth rate: Medium
- Traits: Tolerates wet soil, Rare
- Sold as: Saplings, Seed

Heights and zones are typical ranges for the species in cultivation; local conditions and seed source shift them.

## Availability

Not yet priced online. Ask at captain@bluewhaletrees.com or leave an email on the web page to be told when it is listed.

## Notes

Swamp cottonwood is the poplar of the wettest bottoms, growing on sites too wet for eastern cottonwood. Despite its name it is not a true cottonwood but belongs to a group of poplars with round leaf stalks. It is uncommon in most of its range, rare in tree collections and hard to grow from cuttings. Connecticut, Massachusetts and Michigan list it as endangered, and New York lists it as threatened. Plant it at a swamp edge, in a wet swale or on a pond margin where water stands through the spring.

## Size, growth and what to expect

Swamp cottonwood grows at a medium rate, about a foot and a half a year in our growth estimator. On poorly drained ground, height growth has averaged about 2½ feet a year over 30 years. Expect 70 to 90 feet. It grows little after 40 or 50 years and seldom stays sound past 80.

Catkins open from March to May, before the leaves. From April into July, female trees shed tiny seeds on tufts of cotton that ride the wind and float on floodwater. The leaves, up to 8 inches long, open coated in white down.

It grows wild in swamps and wet bottoms from Connecticut to northwestern Florida and Louisiana, and up the Mississippi Valley to Missouri, Ohio and southern Michigan. In 2003 it was discovered in southern Ontario, at that time the most recently found Canadian tree.

## How to grow Swamp Cottonwood

Swamp cottonwood needs full sun, since older trees will not stand shade. It is most often found on heavy clay and grows best in the deep, moist soil of shallow swamps. Give it a slough, a swamp edge or a low flat where the water table stays near the surface for all but two or three months a year. Poplar roots run shallow and far, so plant it 30 feet from a wall and more than 50 feet from overhead wires, and set trees 40 feet apart.

Saplings ship bare-root or potted. Plant them dormant, from leaf fall until bud swell, in a hole wider than the roots and no deeper. Set the root flare at the soil line, put the native soil back in, and keep the mulch clear of the trunk. The cottony seed lives only a week or two, so sow it the day it arrives. Scatter it on the surface of wet, bare soil, uncovered, and keep the bed moist until the seedlings are up.

Water weekly through the first summer unless the ground stays wet. Rabbits and deer browse seedlings and young trees, so cage them for the first few years. Prune only to keep one leader, in the dormant season.

Trees are male or female, and only females bear the cottony seed, from about 10 years old. No pest or disease is recorded for swamp cottonwood alone, but those of eastern cottonwood probably attack it. They include the cottonwood leaf beetle, borers, leaf rust and cankers. Where eastern cottonwood grows nearby the two can cross.

## Sources

- [USDA Forest Service, Silvics of North America: swamp cottonwood (1990)](https://research.fs.usda.gov/silvics/swamp-cottonwood)
- [USDA Forest Service, Woody Plant Seed Manual: Populus chapter](https://www.fs.usda.gov/nsl/Wpsm/Populus.pdf)
- [NC State Extension Gardener Plant Toolbox: Populus heterophylla](https://plants.ces.ncsu.edu/plants/populus-heterophylla/)
- [Lady Bird Johnson Wildflower Center: Populus heterophylla](https://www.wildflower.org/plants/result.php?id_plant=POHE4)
- [Flora of North America, vol. 7: Populus heterophylla](http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=242417040)
- [Michigan Natural Features Inventory: Special Plant Abstract for Populus heterophylla (Penskar and Crispin 2010)](https://mnfi.anr.msu.edu/abstracts/botany/Populus_heterophylla.pdf)
- [New York Natural Heritage Program: Swamp Cottonwood, Populus heterophylla, conservation guide](https://guides.nynhp.org/swamp-cottonwood/)
- [Connecticut Department of Energy and Environmental Protection: Endangered, Threatened and Special Concern Plants, effective August 5, 2015](https://portal.ct.gov/deep/endangered-species/endangered-species-listings/endangered-threatened--special-concern-plants)
- [Massachusetts Division of Fisheries and Wildlife: Massachusetts Endangered Species Act list, as listed in 321 CMR 10.90, August 16, 2024](https://www.mass.gov/doc/printable-list-of-endangered-threatened-and-special-concern-species/download)
- [New Jersey Department of Environmental Protection: List of Endangered Plant Species and Plant Species of Concern, January 2024](https://dep.nj.gov/wp-content/uploads/parksandforests/njplantlist.pdf)
- [NatureServe Explorer: Populus heterophylla](https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.136148/Populus_heterophylla)
- [Virginia Tech Dendrology: swamp cottonwood](https://dendro.cnre.vt.edu/dendrology/syllabus/factsheet.cfm?ID=348)
- [Trees and Shrubs Online: Populus heterophylla, from Bean](https://www.treesandshrubsonline.org/articles/populus/populus-heterophylla/)
- [USDA ARS and the PRISM Climate Group, 2023 Plant Hardiness Zone Map ZIP code listing](https://prism.oregonstate.edu/phzm/)

## Read before planting

- [Ten planting mistakes that quietly kill trees](https://bluewhaletrees.com/articles/ten-planting-mistakes/index.html.md)
- [Transplanting young trees: timing, water and protection](https://bluewhaletrees.com/articles/transplanting-young-trees/index.html.md)
- [Protecting young trees from voles, rabbits, deer and squirrels](https://bluewhaletrees.com/articles/protecting-trees-from-animals/index.html.md)
- [How fast native trees grow: a year's growth by species, soil and sun](https://bluewhaletrees.com/articles/how-fast-native-trees-grow/index.html.md)
- [Native trees for insects: the beetles, wasps, cicadas and fireflies that everything else eats](https://bluewhaletrees.com/articles/native-trees-for-insects/index.html.md)
- [Six trees not to plant near a house, and what to plant instead](https://bluewhaletrees.com/articles/trees-not-to-plant-near-a-house/index.html.md)

## Related

- [Planting-site check](https://bluewhaletrees.com/tools/site-check/index.html.md): for a thrive, struggle or fail verdict on Swamp Cottonwood, add ?species=swamp-cottonwood with zone (2 to 10), sun (full, part, shade) and moisture (dry, average, wet) to that address, for example ?species=swamp-cottonwood&zone=6&sun=part&moisture=average.
- [Companion species for Swamp Cottonwood](https://bluewhaletrees.com/tools/companions/index.html.md?species=swamp-cottonwood): the natives that share its ground and the plants that pair with it in a yard.
- [Growth estimator](https://bluewhaletrees.com/tools/growth/index.html.md): how the height and trunk projections are made; the estimate itself runs in the browser at https://bluewhaletrees.com/tools/growth/#species=swamp-cottonwood
- [Seed sowing planner](https://bluewhaletrees.com/tools/sowing/index.html.md): how Swamp Cottonwood is sown, in the chart for every species (treatment, cold days, depth, timing); the dated plan runs in the browser at https://bluewhaletrees.com/tools/sowing/#species=swamp-cottonwood
- [Pollination planner](https://bluewhaletrees.com/tools/pollination/index.html.md): what Swamp Cottonwood needs for a crop and how many to plant, in the table for every species; the planner runs in the browser at https://bluewhaletrees.com/tools/pollination/#plants=swamp-cottonwood:5
- [Bloom and fruit calendar](https://bluewhaletrees.com/tools/calendar/index.html.md): the months Swamp Cottonwood flowers and fruits, in the grid for every species.