Seaside Alder Alnus maritima
Seaside Alder is a perennial tree native to the lower 48 states. It grows to 30 ft and blooms Aug in full sun – part shade, with brown fruit. A keystone plant for native insects and the food web.
More about this plant
Alnus maritima is a species of shrub or small tree in the family Betulaceae. Alnus maritima is endemic to the United States, and is found naturally in three disjunct populations in Oklahoma, Georgia, and in Maryland and Delaware on the Delmarva Peninsula. Wikipedia →
Growing & care
USDA PLANTS · TRY- Sun
- Full sun – part shade
- Soil & moisture
- High moisture
- Soil pH
- 5–7
- Fertility need
- Medium
- Adapts to
- Coarse (sandy), Medium (loam), Fine (clay)
- Hardiness
- USDA zone 8+
- Height
- 30 ft
- Mature width
- ~ 18 ft wide DERIVED derived estimate — open-grown crown allometry (height × growth-form ratio); not a measurement
- Spacing
- 6–12 ft apart from USDA planting density
- Spread
- Slow
- Growth rate
- Moderate
- Growth form
- Single stem
- Lifespan
- Perennial · moderate
- Foliage
- Deciduous broadleaf · medium texture
- Active growth
- Spring & summer
- Fruit
- Brown persists into winter
- Propagate by
- Seed, Bare root, Container
- Seed starting
- Needs cold stratification a cold-moist spell before it germinates
- Seeds ripen
- Summer – Autumn seed-collection / harvest window
- In the trade
- Routinely available
- Deer browsing
- Medium moderately palatable
- Resprouts if cut
- Yes regrows after top-kill
Sow timing keys off your local last- and first-frost dates.
Wildlife & pollinators
How pollinator value is scored →❧ Caterpillar hosts ~255 caterpillar species · keystone genus
Alnus supports ~255 caterpillar species.
Native butterfly & moth caterpillars are the base of the terrestrial food web — most songbirds rear their young almost entirely on them. As a host for native Lepidoptera this is a powerhouse genus.
Recorded feeding on Alnus in North America, including:
+ 8 more species → ↑ show fewer
Related plants
More Alnus →
How we know this (2) Methods & honest limits
We take the plant’s U.S. county range and look up each county’s long-term climate, then summarise: native rainfall = the median annual rainfall across its counties; heat tolerance = the warm end (90th percentile) of average temperature across its range (mirroring how our cold-hardiness floor uses an extreme). Counties + medians blunt the roadside/observer bias that makes point-level climate unreliable. Needs at least five placeable counties.
Honest limits: A realized, sampling-biased niche (where it has been recorded, not its physiological optimum), and county climate is coarse — large Western counties span deserts and mountains. Derived guide, never a measured fact.
For woody plants that have a height but no measured crown, we estimate width = height × a crown-to-height ratio fit for that plant’s form (conifers narrower than broadleaf trees, shrubs widest), calibrated on our measured open-grown crowns and capped at the largest one ever measured. A measured crown always wins; herbaceous plants get nothing (no anchor).
Honest limits: A coarse class-median estimate for garden-scale spacing, not a measurement; woody single/multi-stem forms only.
Sources for this entry (32) Open & cited
Cite this page Open data, please attribute
PlantKey’s data is open under CC BY-SA 4.0 — free to reuse and adapt, with attribution and the same licence. Photos keep their own per-image licence + credit (see Sources above).
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