Plant profile

Alders

Genus Alnus

Alders are fast-growing trees in the genus Alnus that are especially useful in damp spots and along edges where you want quick cover and early-season pollen for insects.

Plant Type

Trees > Alders

Aliases

Alder

Native Range

Varies by species within the genus; many alders are native across northern temperate regions.

Bloom window

Early spring

Overview Summary Impact Recognition Location Requirements Glossary Get Involved

OVERVIEW

About This Plant

Alders (genus Alnus) are a smart choice when you need a hardy tree for a site that stays damp or has heavier soil. Instead of big, colorful blossoms, alders bloom with catkins—flower clusters that show up early in spring. That timing can matter: when the season is just starting, early-flying insects may be looking for pollen sources.

In a habitat-focused planting, think of alders as a “structure” plant. They can help create shade and shelter, and they pair well with a mix of flowering perennials and shrubs that take over the nectar-and-pollen job later in the year. If you’re planting on a school campus or in a small yard, the biggest success factor is space—choose a spot where a tree can grow without constant pruning or conflicts with paths and buildings.

If you’re not sure which alder is right for your area, start by checking what’s locally appropriate and what fits your site (especially moisture and available room).

Best role for pollinators

Moist sites, naturalized edges, and early-season pollen support

Alders (*Alnus* spp.) — https://www.inaturalist.org/photos/299499275 Photo: (c) Radha Veach, some rights reserved (CC BY-NC) | CC-BY-NC | iNaturalist

FAST FACTS

Quick Details

Essential stats and requirements for quick reference.

Category	Details
Also known as	Alder
Bloom window	Early spring
Typical height	Small to medium tree (varies by species)
Pollinators supported	Early-season bees
Light & moisture	Sun to part shade; medium to wet soil
Best roles for pollinators	Moist sites, naturalized edges, and early-season pollen support

SUMMARY

If You Remember Three Things

A quick scan of what they do, what they need, and the best first step.

What they do

Alders add quick tree cover and offer early catkins that can help insects get started in spring.

What they need

Room to grow and soil that doesn’t stay bone-dry, especially while the tree is getting established.

One best action

Choose a spot with consistent moisture and give the tree enough space from sidewalks, fences, and foundations.

IMPACT

Why Plant This?

Alders are a practical habitat tree: they can handle moist soils, add quick structure, and provide early-season catkins that may help pollinators when spring is just beginning.

Alder “cones” are actually small, woody structures that hold the seeds and often stay on the branches after leaves drop.

Key Impacts

What it Supports

Early catkins can provide pollen when few other plants are flowering.
Trees add structure—shade, wind protection, and nesting cover—that smaller plants can’t provide.
Alders can be a practical choice for damp or low-lying areas where other trees struggle.

RECOGNITION

Identification Guide

Alders can look a bit like birches at a glance, but a few clues make them easier to spot.

Leaves

Simple, rounded to oval leaves; edges may be slightly toothed; leaves are arranged alternately on the twig.

Flowers

Catkins; typically appear in early spring, often before full leaf-out.

Fruits

Small, woody cone-like clusters that hold seeds and may remain on branches.

LOCATION

Where It Grows

Native environments and the best spots to place it in your landscape.

Habitats

Wetlands and wet edges
Stream and pond margins
Moist woods and low areas
Naturalized urban edges

Where it is often used

Moist-area tree for edges, swales, and low spots
Naturalized screen or windbreak (where space allows)
Schoolyard habitat tree to add shade and structure
Streamside or pond-edge planting (where appropriate and permitted)

SEASONALITY

When It Blooms

Notes on bloom windows and how this plant helps pollinators across the seasons.

Bloom window

Alders bloom early, before many garden flowers are open.

Bloom Season Role: Early-season pollen source (catkins)

Seasonal benefits

Catkins can offer pollen at a time when pollinators are searching for their first meals.
Early bloom helps spread resources across the season when paired with later-flowering plants.

REQUIREMENTS

What It Needs

The right mix of sun, soil, and space for healthy growth.

Sun exposure

Full sun to part shade.

Soil type

Moist, well-drained to wet soils; tolerates heavier soils in many settings.

Moisture needs

Water regularly during the first season; after establishment, alders are often more forgiving in consistently moist sites.

Planting method

Plant in a spot with room for canopy and roots; keep away from tight corners, narrow boulevards, and building foundations.

Mulching tips

Mulch a wide ring to reduce weeds and protect the trunk; keep mulch pulled back from direct contact with the bark.

GARDENING GUIDE

How to Grow It

Simple steps to plant, prune, and maintain healthy trees without pesticides.

Planting tips

Pick a location with enough space for a tree canopy and where soil stays moderately moist.
Dig a hole as deep as the root ball and wider than it.
Set the tree so the top of the root ball is level with the surrounding soil.
Backfill, firm gently, and water slowly and deeply.
Mulch a wide ring and protect the trunk from mower or trimmer damage.

Seasonal care

Water during dry periods for the first year or two while roots establish.
Keep grass and weeds from competing right at the base (mulch helps).
Prune only as needed to remove broken or crossing branches; avoid heavy pruning during active growth.
If catkins or seed clusters drop on paths, place the tree where cleanup is easy or where leaf litter can stay.

What not to do

Planting an alder in a spot that’s too small.
Letting a newly planted tree dry out.
Spraying pesticides on or near the tree during bloom.

Pairings

Best Pairings for Season-Long Bloom

Pairing ideas to keep pollinators fed throughout the growing season.

Early Bloom

Early-blooming native wildflowers (choose locally appropriate species)

Mid-Season Bloom

Summer-blooming pollinator flowers (choose locally appropriate species)

Late-Season Bloom

Late-season flowers for fall foraging (choose locally appropriate species)

“Alder” can mean different species depending on your region. If you’re planting in Toronto, choose a locally appropriate alder species and confirm it fits the space and site conditions.

GLOSSARY