Seaside Alder (Alnus maritima)

Seaside Alder

Alnus maritima

It blooms late when other trees rest, a quiet autumn beauty. Deciduous small tree or large shrub; common name: seaside alder.

Full sun
2–3/week
Beginner
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Plant Needs

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Sunlight Full sun to partial shade; tolerates coastal salt spray and wet soil conditions
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Watering Keep soil consistently moist; tolerates occasional flooding, avoid prolonged drought stress
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Temperature Hardy to -15°C; adapts to temperate coastal climates, withstands mild summer heat
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Characteristics

  • Leaf: Simple oval to obovate leaves with serrated margins; dark green above, paler beneath, turning yellow in fall
  • Flower: Monoecious; pendulous yellow-brown male catkins and small upright reddish-green female catkins maturing into woody cones
  • Stem: Slender gray-brown bark; young stems have soft reddish pubescence
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Care Guide

Watering

Maintain consistently moist soil; water deeply during extended dry spells

Fertilization

Light slow-release feed once in early spring. Use balanced, low-nitrogen feed to support healthy growth without excessive foliage production

Eggshell powder top-dressing:Crush dried eggshells into fine powder; sprinkle lightly on soil surface and gently work into the top layer to add calcium without altering soil pH
Pruning
  • Remove dead or damaged branches in late winter before new growth emerges
  • Thin crowded stems to improve airflow and maintain a balanced, open shape
  • Prune lightly in early spring to control size and encourage more abundant flowering
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Toxicity

Warning: this plant may be toxic.

Pets & Humans

Pets: ASPCA: Non-toxic to cats

Humans: No known toxicity to humans

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Garden Uses & Culture

Culture: N/A

Usage: Soil stabilization in wet coastal areas; ornamental autumn flowering plant for pollinator support