# Smooth Alder (Alnus serrulata)

> A nitrogen-fixing streambank shrub that holds soil, feeds woodcock and grouse, and thrives in standing water.

Also called hazel alder, tag alder, swamp alder. Category: Native Shrubs. Grown from seed by Blue Whale Trees. Web version: https://bluewhaletrees.com/plants/smooth-alder/

![Smooth alder (Alnus serrulata) toothed oval leaves in summer](https://bluewhaletrees.com/img/plants/smooth-alder-h1610-800.jpg)
*Photo: Fepup, Public domain · [Wikimedia Commons](https://commons.wikimedia.org/wiki/File:Alnus_serrulata_4.JPG)*

## Facts

- Type: Shrub
- Mature height: 10 to 20 ft
- USDA hardiness zones: 4 to 9
- Grows wild in: Stream banks, swamps and wet flats
- Native range: 30 states and [the District of Columbia](https://bluewhaletrees.com/tools/native/index.html.md?state=DC), north to [Maine](https://bluewhaletrees.com/tools/native/index.html.md?state=ME), south to [Florida](https://bluewhaletrees.com/tools/native/index.html.md?state=FL) and west to [Texas](https://bluewhaletrees.com/tools/native/index.html.md?state=TX) ([Alabama](https://bluewhaletrees.com/tools/native/index.html.md?state=AL), [Arkansas](https://bluewhaletrees.com/tools/native/index.html.md?state=AR), [Connecticut](https://bluewhaletrees.com/tools/native/index.html.md?state=CT), [Delaware](https://bluewhaletrees.com/tools/native/index.html.md?state=DE), [Florida](https://bluewhaletrees.com/tools/native/index.html.md?state=FL), [Georgia](https://bluewhaletrees.com/tools/native/index.html.md?state=GA), [Illinois](https://bluewhaletrees.com/tools/native/index.html.md?state=IL), [Indiana](https://bluewhaletrees.com/tools/native/index.html.md?state=IN), [Kansas](https://bluewhaletrees.com/tools/native/index.html.md?state=KS), [Kentucky](https://bluewhaletrees.com/tools/native/index.html.md?state=KY), [Louisiana](https://bluewhaletrees.com/tools/native/index.html.md?state=LA), [Maine](https://bluewhaletrees.com/tools/native/index.html.md?state=ME), [Maryland](https://bluewhaletrees.com/tools/native/index.html.md?state=MD), [Massachusetts](https://bluewhaletrees.com/tools/native/index.html.md?state=MA), [Mississippi](https://bluewhaletrees.com/tools/native/index.html.md?state=MS), [Missouri](https://bluewhaletrees.com/tools/native/index.html.md?state=MO), [New Hampshire](https://bluewhaletrees.com/tools/native/index.html.md?state=NH), [New Jersey](https://bluewhaletrees.com/tools/native/index.html.md?state=NJ), [New York](https://bluewhaletrees.com/tools/native/index.html.md?state=NY), [North Carolina](https://bluewhaletrees.com/tools/native/index.html.md?state=NC), [Ohio](https://bluewhaletrees.com/tools/native/index.html.md?state=OH), [Oklahoma](https://bluewhaletrees.com/tools/native/index.html.md?state=OK), [Pennsylvania](https://bluewhaletrees.com/tools/native/index.html.md?state=PA), [Rhode Island](https://bluewhaletrees.com/tools/native/index.html.md?state=RI), [South Carolina](https://bluewhaletrees.com/tools/native/index.html.md?state=SC), [Tennessee](https://bluewhaletrees.com/tools/native/index.html.md?state=TN), [Texas](https://bluewhaletrees.com/tools/native/index.html.md?state=TX), [Vermont](https://bluewhaletrees.com/tools/native/index.html.md?state=VT), [Virginia](https://bluewhaletrees.com/tools/native/index.html.md?state=VA), [West Virginia](https://bluewhaletrees.com/tools/native/index.html.md?state=WV) and [the District of Columbia](https://bluewhaletrees.com/tools/native/index.html.md?state=DC))
- Sun: Full, Part
- Soil moisture: Wet
- Growth rate: Fast
- Flowers: March to April
- Fruit: Cones, September to February
- First crop: About 2 years
- Mature spread: 15 ft
- Traits: Tolerates wet soil, Wildlife value, Nitrogen fixing, Winter interest, Erosion control
- Sold as: Saplings, Seed

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

## Availability

Saplings ship [bare-root](https://bluewhaletrees.com/articles/planting-bare-root-trees-on-arrival/index.html.md) or [in a pot](https://bluewhaletrees.com/articles/a-sapling-in-a-pot/index.html.md), [usually 12 to 18 inches tall](https://bluewhaletrees.com/articles/small-sapling-or-big-transplant/index.html.md), in the dormant season, and their [height and age](https://bluewhaletrees.com/articles/reading-a-nursery-listing/index.html.md) are stated with the price, once available. Live plants ship February to May and October to November. Not priced yet: leave an email on the web page for one email when it is priced, with a code for 10% off the plants in that order, not shipping or tax, or write to captain@bluewhaletrees.com.

In bundles: Wet Spot Pack.

## Notes

Smooth alder lines slow streams and pond edges across the eastern states. Its roots fix nitrogen and knit wet banks together, its catkins feed early bees and its cone-like fruits feed finches all winter. Plant it to stabilize a wet ditch or shoreline, or as a nurse shrub around young bottomland trees. A screen for wet ground first, and woodcock cover second.

## Size, growth and what to expect

Smooth alder feeds itself. Root nodules fix nitrogen, which makes it a pioneer for reclaiming bare wet ground. It grows fast, nearly three feet a year in its youth on an average site in our growth estimator's model. It makes a multi-stemmed, suckering shrub or small tree 10 to 20 feet tall and 8 to 15 feet wide that spreads into a thicket.

Male catkins 1½ to 2½ inches long and half-inch red female catkins open in March and April. The female catkins ripen into inch-long cones that turn dark brown in fall and hang on through winter, and birds feed on the seed. Deer browse the foliage, birds and small mammals eat the pollen-rich male catkins in spring, and it hosts the caterpillars of the harvester butterfly.

It grows wild from Nova Scotia west to Illinois and Missouri and south to east Texas and north Florida. Its home is boggy ground along streams, lakes and rivers, wet meadows, ditches and swamp borders.

## How to grow Smooth Alder

Smooth alder wants its feet wet: a stream bank, a pond shore or a ditch, in full sun or light shade. Do not put it in a dry bed. Clumps spread by suckers, so keep it 10 feet from a building and 6 feet between plants along a shore.

Plant dormant saplings, bare-root or potted, between leaf drop and bud swell, in a hole wider than the roots and no deeper, crown at the soil line, native mud back in. It fixes its own nitrogen, so skip fertilizer. Seed is tiny: chill it damp for a month, then sow on the surface of wet mix in spring, uncovered, and keep it wet under a screen.

Water only if the site dries the first summer. Deer, rabbits and beaver chew alder, so cage it for two years where they visit. It needs no pruning; a clump cut to the ground in late winter resprouts.

Smooth alder carries male and female flowers on the same shrub, but alders set little seed with their own pollen. Plant two or more from different parents so the wind can carry pollen between them. Expect a thicket, not a specimen; smooth alder suckers into a bank-holding colony. Catkins open in late winter before the leaves. Flea beetles chew leaves in summer and woolly aphids cluster on twigs; both are harmless.

## Sources

- [NC State Extension Gardener Plant Toolbox: Alnus serrulata](https://plants.ces.ncsu.edu/plants/alnus-serrulata/)
- [Missouri Botanical Garden Plant Finder: Alnus serrulata](https://plantfinder.mobot.org/PlantFinderDetails.aspx?taxonid=277828)
- [Lady Bird Johnson Wildflower Center: Alnus serrulata](https://www.wildflower.org/plants/result.php?id_plant=ALSE2)
- [USDA NRCS PLANTS Database: Alnus serrulata](https://plants.usda.gov/plant-profile/ALSE2)
- [USDA Forest Service, Woody Plant Seed Manual (2008), Alnus chapter, Harrington and others](https://www.fs.usda.gov/nsl/Wpsm/Alnus.pdf)
- [USDA NRCS Plant Fact Sheet: smooth alder, Alnus serrulata](https://plants.sc.egov.usda.gov/DocumentLibrary/factsheet/pdf/fs_alse2.pdf)
- [NatureServe Explorer: Alnus serrulata, Brookside Alder](https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.138391/Alnus_serrulata)
- [Go Botany, Native Plant Trust: Alnus serrulata](https://gobotany.nativeplanttrust.org/species/alnus/serrulata/)
- [Trees and Shrubs Online: Alnus serrulata, Baxter and McAllister (2024)](https://www.treesandshrubsonline.org/articles/alnus/alnus-serrulata/)
- [Flora of North America, vol. 3: Alnus serrulata](http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=233500040)
- [Native Plant Network, propagation protocol: Alnus serrulata](https://npn.rngr.net/renderNPNProtocolDetails?selectedProtocolIds=betulaceae-alnus-3492)

## 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)
- [Why reservoirs and drinking watersheds are surrounded by forest, and what the trees do for the water](https://bluewhaletrees.com/articles/why-reservoirs-are-surrounded-by-forest/index.html.md)
- [Trees and shrubs that soak up water: what they can do for a wet yard, and the natives for a rain garden](https://bluewhaletrees.com/articles/trees-that-soak-up-water/index.html.md)
- [The habitat around a tree is part of the tree](https://bluewhaletrees.com/articles/habitat-around-a-tree/index.html.md)

## Related

- Other alders (Alnus) we grow: [Green Alder](https://bluewhaletrees.com/plants/green-alder/index.html.md), [Seaside Alder](https://bluewhaletrees.com/plants/seaside-alder/index.html.md)
- Plants that share its sun and soil: [Winterberry Holly](https://bluewhaletrees.com/plants/winterberry/index.html.md), [Buttonbush](https://bluewhaletrees.com/plants/buttonbush/index.html.md), [Swamp Azalea](https://bluewhaletrees.com/plants/swamp-azalea/index.html.md) and [Sweet Pepperbush (Summersweet)](https://bluewhaletrees.com/plants/sweet-pepperbush/index.html.md)
- Trees to plant it under: [River Birch](https://bluewhaletrees.com/plants/river-birch/index.html.md), [American Elm](https://bluewhaletrees.com/plants/american-elm/index.html.md) and [Atlantic White Cedar](https://bluewhaletrees.com/plants/atlantic-white-cedar/index.html.md)
- Same size, similar character: [Green Alder](https://bluewhaletrees.com/plants/green-alder/index.html.md), [Seaside Alder](https://bluewhaletrees.com/plants/seaside-alder/index.html.md), [Pondberry](https://bluewhaletrees.com/plants/pondberry/index.html.md) and [Odorless Bayberry](https://bluewhaletrees.com/plants/odorless-bayberry/index.html.md)
- [Planting-site check](https://bluewhaletrees.com/tools/site-check/index.html.md): for a thrive, struggle or fail verdict on Smooth Alder (Swamp Alder), add ?species=smooth-alder with zone (2 to 10), sun (full, part, shade) and moisture (dry, average, wet) to that address; for example, the verdict for zone 4, part sun and average soil as Markdown is at https://bluewhaletrees.com/tools/site-check/index.html.md?species=smooth-alder&zone=4&sun=part&moisture=average
- [Companion species for Smooth Alder (Swamp Alder)](https://bluewhaletrees.com/tools/companions/index.html.md?species=smooth-alder): the natives that share its ground and the plants that pair with it in a yard.
- [Tree growth estimator](https://bluewhaletrees.com/tools/growth/index.html.md): how the height and trunk projections are made; the estimate for Smooth Alder (Swamp Alder) as Markdown is at https://bluewhaletrees.com/tools/growth/index.html.md?species=smooth-alder (add height=, years= and site= poor, average or good)
- [Seed sowing planner](https://bluewhaletrees.com/tools/sowing/index.html.md): how Smooth Alder (Swamp Alder) is sown, in the chart for every species (treatment, cold days, depth, timing); the dated plan for it as Markdown is at https://bluewhaletrees.com/tools/sowing/index.html.md?species=smooth-alder (add state= and zone= for your own frost dates, method=fridge for the refrigerator route)
- [Pollination planner](https://bluewhaletrees.com/tools/pollination/index.html.md): what Smooth Alder (Swamp Alder) needs for a crop and how many to plant, in the table for every species; the verdict for 2 of them as Markdown is at https://bluewhaletrees.com/tools/pollination/index.html.md?plants=smooth-alder:2
- [Planting-window tool](https://bluewhaletrees.com/tools/planting-window/index.html.md): when to plant Smooth Alder (Swamp Alder) where you live, as a fall and a spring window from the local frost dates; the windows as Markdown are at https://bluewhaletrees.com/tools/planting-window/index.html.md?species=smooth-alder&state=MO&zone=6 with your own state and zone in place of those
- [Planting-distance tool](https://bluewhaletrees.com/tools/distance/index.html.md): how far Smooth Alder (Swamp Alder) goes from a house, a septic field, a walk, wires, a property line and the next tree; the distances as Markdown are at https://bluewhaletrees.com/tools/distance/index.html.md?species=smooth-alder&near=house,septic,pavement,wires,boundary,tree
- [Bloom and fruit calendar](https://bluewhaletrees.com/tools/calendar/index.html.md): the months Smooth Alder (Swamp Alder) flowers and fruits, in the grid for every species; its own row and the gaps of a planting with it as Markdown at https://bluewhaletrees.com/tools/calendar/index.html.md?plants=smooth-alder