# Seaside Alder (Alnus maritima) > The one native alder that blooms in fall, hanging gold catkins in August and September on a rare shrub that stands in water and feeds its own soil. Also called brook alder, beach alder. Category: Native Shrubs. Grown from seed by Blue Whale Trees. Web version: https://bluewhaletrees.com/plants/seaside-alder/ ![Seaside alder (Alnus maritima) glossy leaves and yellow male catkins in late summer bloom](https://bluewhaletrees.com/img/plants/seaside-alder-h1610-800.jpg) *Photo: Robert H. Mohlenbrock, Public domain ยท [Wikimedia Commons](https://commons.wikimedia.org/wiki/File%3AAlnus_maritima_leaves_catkin.jpg)* ## Facts - Type: Shrub - Mature height: 12 to 30 ft - USDA hardiness zones: 3 to 9 - Grows wild in: Stream banks, swamps and wet flats - Native range: Delaware, Georgia, Maryland and Oklahoma - Sun: Full, Part - Soil moisture: Wet, Average - Growth rate: Medium - Traits: Rare, Showy flowers, Tolerates wet soil, Nitrogen fixing, Hedge or screen, Wildlife value - 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 Seaside alder is a many-stemmed shrub or small tree that survives in the wild in three stands hundreds of miles apart. One lines the rivers of the Delmarva Peninsula, one follows two creeks in south-central Oklahoma, and one grows around a single pond in northwest Georgia. Each is now its own subspecies, and genetic work says the gaps come from a range that shrank long ago, not from planting. NatureServe ranks it vulnerable, and every state it grows in treats it as rare. Plant it to screen a pond shore or a rain garden, where its catkins light up September. ## Size, growth and what to expect Seaside alder grows at a medium pace, about a foot and a half a year in our growth estimator. In gardens it reaches 20 to 30 feet tall and 16 to 30 feet wide. Wild Delmarva shrubs run nearer 12 to 20 feet. It flowers about 2 years from seed. Its catkins open in August and September, after every other native alder has finished. The small woody cones take about a year to ripen, and the seed falls from December to March (Graves and Schrader). The dense leaves give birds cover for nests. It grows at the edges of ponds and small streams, often standing in water. All three wild stands sit where winters are mild, yet all 450 plants in field trials survived winters as cold as zone 3a (Schrader and Graves 2003). ## How to grow Seaside Alder Seaside alder wants full sun or light shade and a soil that stays moist to wet. It will stand in water, and it takes flooding, clay and alkaline ground. Once rooted it rides out a short drought, but it is not a plant for a dry bed. Set plants 10 feet apart for a screen, and keep them 15 feet from a wall and 15 feet from overhead wires. 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 crown at the soil line, put the native soil back in, and skip fertilizer, since the roots fix their own nitrogen. Seed needs six to eight weeks of cold, damp storage in the refrigerator. Sow it in spring barely covered, about a fifth of an inch deep, and keep the mix wet. Water weekly through the first two summers unless the ground stays wet. In a trial on dry Utah soils, plants left unwatered died within a month of leafing out. Deer and rabbits chew young alders, so cage them for two winters where they visit. It needs little pruning. Cut out dead stems in late winter. Seaside alder carries male and female flowers on the same shrub and the wind pollinates it, so one shrub sets seed alone. Seed from the Delmarva stand germinates far less often than seed from Oklahoma or Georgia. No serious pest or disease troubles it, though cankers, alder aphids and leaf miners can show up. ## Sources - [Flora of North America, vol. 3: Alnus maritima](http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=233500036) - [NatureServe Explorer: Alnus maritima](https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.154229/Alnus_maritima) - [Missouri Botanical Garden Plant Finder: Alnus maritima](https://plantfinder.mobot.org/PlantFinderDetails.aspx?taxonid=277840) - [Missouri Botanical Garden Plant Finder: Alnus maritima subsp. oklahomensis 'September Sun'](https://plantfinder.mobot.org/PlantFinderDetails.aspx?taxonid=267250) - [NC State Extension Gardener Plant Toolbox: Alnus maritima](https://plants.ces.ncsu.edu/plants/alnus-maritima/) - [The Morton Arboretum: Seaside alder](https://mortonarb.org/plant-and-protect/trees-and-plants/seaside-alder/) - [Chicago Botanic Garden](https://www.chicagobotanic.org/plant-information/plant-finder/alnus-maritima-seaside-alder) - [Lady Bird Johnson Wildflower Center: Alnus maritima](https://www.wildflower.org/plants/result.php?id_plant=ALMA7) - [Trees and Shrubs Online, International Dendrology Society: Alnus maritima](https://www.treesandshrubsonline.org/articles/alnus/alnus-maritima/) - [Schrader and Graves 2000, Seed germination and seedling growth of Alnus maritima from its three disjunct populations, J. Amer. Soc. Hort. Sci. 125: 128-134](https://doi.org/10.21273/JASHS.125.1.128) - [Schrader and Graves 2003, Phenology and depth of cold acclimation in the three subspecies of Alnus maritima, J. Amer. Soc. Hort. Sci. 128: 330-336](https://doi.org/10.21273/JASHS.128.3.0330) - [Kratsch 2008, Alnus maritima ssp. oklahomensis performance in non-irrigated landscapes in the Intermountain West, J. Environ. Hort. 26: 229-234, USDA Forest Service Treesearch](https://research.fs.usda.gov/treesearch/35284) - [Gibson, Rice and Stucke 2008, Comparison of population genetic diversity between a rare, narrowly distributed species and a common, widespread species of Alnus, Am. J. Bot. 95: 588-596](https://doi.org/10.3732/ajb.2007316) - [Graves and Schrader, US Plant Patent PP18,101, seaside alder 'September Sun', Iowa State University Research Foundation, 2007](https://patents.google.com/patent/USPP18101) - [Iowa State University, Committee for Agricultural Development: Seaside Alder](https://www.cad.iastate.edu/seaside-alder) - [USDA Forest Service, Woody Plant Seed Manual (2008), Alnus chapter](https://rngr.net/publications/wpsm/genera/a/at_download/file) ## 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 native trees become rare, and ten rare eastern species worth growing](https://bluewhaletrees.com/articles/why-native-trees-become-rare/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) - [The habitat around a tree is part of the tree](https://bluewhaletrees.com/articles/habitat-around-a-tree/index.html.md) ## Related - [Planting-site check](https://bluewhaletrees.com/tools/site-check/index.html.md): for a thrive, struggle or fail verdict on Seaside Alder, add ?species=seaside-alder with zone (2 to 10), sun (full, part, shade) and moisture (dry, average, wet) to that address, for example ?species=seaside-alder&zone=3&sun=part&moisture=average. - [Companion species for Seaside Alder](https://bluewhaletrees.com/tools/companions/index.html.md?species=seaside-alder): 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=seaside-alder - [Seed sowing planner](https://bluewhaletrees.com/tools/sowing/index.html.md): how Seaside Alder 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=seaside-alder - [Pollination planner](https://bluewhaletrees.com/tools/pollination/index.html.md): what Seaside Alder 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=seaside-alder:1 - [Bloom and fruit calendar](https://bluewhaletrees.com/tools/calendar/index.html.md): the months Seaside Alder flowers and fruits, in the grid for every species.