Alder Trees and Shrubs

Members of the Alnus Genus

Alder trees and shrubs (Alnus spp.) are found in the Betulaceae (birch family). Almost all of them are deciduous. These are fast-growing trees and shrubs, so they can be used to help fill in a landscape and provide shade sooner than other species. They do love areas with moist or wet soil with good drainage if available. If the roots are established, they can tolerate a little drought.

These are monoecious, so you will have both male and female flowers present on each plant.  They present as...MORE catkins, with the males being longer than the females. Once the females are pollinated, the catkins mature and become woody. The are somewhat similar in appearance to the cones found on conifers. The dry fruit (a winged samara) is housed inside.

This genus is able to fixate nitrogen. In many plants, they are not able to harness the nitrogen that is naturally found in the atmosphere, so they have to rely on what is present in the soil or be fertilized. Plants with nitrogen fixation capabilities form symbiotic relationships with bacteria that allow them to capture that element. In the case of alders, it is with the Frankia bacteria. This quality allows them to grow on less fertile soils where other plants may struggle.

These trees and shrubs can be an integral part of a butterfly garden since there are many different species that use the leaves as larval food. Birds like to eat the seeds. Catkins are able to be eaten by humans (though not very tasty) and are a source of protein.

Alder wood is one of two kinds used to make Fender guitar bodies, with ash being the other one. According to Fender's site, alder was first chosen because it was plentiful.  It also has good sound properties and is easy to finish with stains. The two most common species used to make their guitars are the black alder (Alnus glutinosa) and the red alder (Alnus rubra).

Alder is considered to be a hardwood and is used frequently to make cabinets, doors, furniture, flooring and other products. Knotty alder is a popular choice for a more rustic look.

  • 01 of 08

    Black Alder

    Picture of the black alder
    Image by Nuuuuuuuuuuul under a Flickr Creative Commons Attribution-ShareAlike License
    • Latin Name: Alnus glutinosa
    • Other Common Names: Common alder, European alder, aller, aar
    • Native to: Europe, northern Africa and western Asia
    • USDA Zones: 3-7
    • Height: 40-60' tall
    • Exposure: Full sun to part shade

    This species of alder has been used in many ways over the year. It can provide lumber, wood for smoking, dyes and herbal medicines. It can become invasive in some areas.

    If you like leaves that are dissected (divided into many sections), look for the 'Laciniata' and...MORE 'Imperialis' cultivars.

  • 02 of 08

    Green Alder

    Picture of the Green Alder
    Image by Matt Lavin under a Flickr Creative Commons Attribution-ShareAlike License
    • Latin Name: Alnus viridis
    • Other Common Names: Mountain alder
    • Native to: Western Hemisphere
    • USDA Zones: Depends on subspecies
    • Height: Depends on subspecies
    • Exposure: Full sun to part shade

    The green alder is one of the smaller species and is a large shrub or small tree.

    There are several different subspecies found throughout the world. They are Alnus viridis subsp. crispa (sometimes seen as A. crispa), A. viridis subsp. fruticosa, A. viridis subsp. viridis, A. viridis subsp. maximowiczii (sometimes A. m...MOREaximowiczii), A. viridis subsp. sinuata (sometimes A. sinuata) and A. viridis subsp. suaveolens.

  • 03 of 08

    Gray Alder

    Picture of the grey alder
    Image by Superior National Forest under a Flickr Creative Commons Attribution-ShareAlike License
    • Latin Name: Alnus incana
    • Other Common Names: Speckled alder, mountain alder, thinleaf alder, tag alder
    • Native to: Europe and North America
    • USDA Zones: Depends on subspecies
    • Height: Depends on subspecies
    • Exposure: Full sun

    There are six different subspecies of the gray alder: subsp. incana, subsp. hirsuta, subsp. kolaensis, subsp. oblongifolia, subsp. rugosa and subsp. tenuifolia.

  • 04 of 08

    Hazel Alder

    Picture of the hazel alder
    Image by ricktree under a Flickr Creative Commons Attribution-ShareAlike License
    • Latin Name: Alnus serrulata
    • Other Common Names: Smooth alder, tag alder, common alder, swamp alder, brookside alder
    • Native to: Eastern North America
    • USDA Zones: 5-9
    • Height: 10-20' tall
    • Exposure: Full sun to part shade

    This species is either a shrub or small tree. It tends to clone itself through suckers. The species name serrulata refers to the margins (edges) of the leaves, which are toothed.

    Continue to 5 of 8 below.
  • 05 of 08

    Italian Alder

    Picture of the Italian alder
    Image by nottsexminer under a Flickr Creative Commons Attribution-ShareAlike License
    • Latin Name: Alnus cordata
    • Other Common Names: European alder
    • Native to: Corsica and southern Italy
    • USDA Zones: 6-9
    • Height: Usually 30-50', but can be up to 80' tall
    • Exposure: Full sun to part shade

    The species name cordata tips you off that this has cordate (heart-shaped) leaves. This species is a recipient of the Award of Garden Merit from the Royal Horticultural Society.

  • 06 of 08

    Red Alder

    Picture of the red alder
    Image by Holy Outlaw under a Flickr Creative Commons Attribution-ShareAlike License
    • Latin Name: Alnus rubra
    • Other Common Names:  Pacific Coast alder, Oregon alder, western alder
    • Native to: Western United States
    • USDA Zones: 5-9
    • Height: 40-120' tall depending on growing conditions
    • Exposure: Full sun

    If you are in the Pacific Northwest, the red alder is the hardwood that you are most likely to come across. You can identify this alder species from the others in the genus by the fact that the margins of the leaves curl under. The bark can be used to make different colors of dyes.

  • 07 of 08

    Seaside Alder

    Picture of the seaside alder
    Image by Robert H. Mohlenbrock USDA-NRCS PLANTS Database
    • Latin Name: Alnus maritima
    • Other Common Names: Beach alder
    • Native to: Eastern United States and southern Oklahoma
    • USDA Zones: 3-7
    • Height: 12-20' tall
    • Exposure: Full sun to part shade, full sun is best

    The seaside alder blooms in the fall, while most of the other alder species produce flowers in the spring.

    The species name of maritima is used because this is naturally found along the eastern coast of the United States. A synonym is Alnus metroporina. There are three different subspecies of the...MORE seaside alder: subsp. georgiensis, subsp. oklahomensis and subsp. maritima.

  • 08 of 08

    White Alder

    Picture of the white alder
    Image by briweldon under a Flickr Creative Commons Attribution License
    • Latin Name: Alnus rhombifolia
    • Other Common Names: Sierra alder, California white alder
    • Native to: Western North America
    • USDA Zones: 6-10
    • Height: 30-100' tall
    • Exposure: Full sun to part shade

    This is called the white alder because of how light green in color the leaves are. The species name rhombifolia indicates that the leaves are shaped like a rhombus.