Alder (Alnus × mayrii)
The Alder (Alnus × mayrii) is a tough, medium-sized deciduous tree thriving in wet soils. Ideal for rain gardens and difficult sites.
Complete Plant Information
Overview
The Alnus × mayrii, commonly known as Alder, is a vigorous, medium-sized deciduous tree valued for its adaptability to challenging soil conditions. This hybrid provides a sturdy structure, typically reaching 30 to 50 feet tall, making it an excellent choice where robust growth is required. Its deep root system combined with tolerance for wetness offers significant functional value in landscape design.
This hybrid Alder arises naturally where Alnus japonica and Alnus hirsuta overlap in their native ranges of Korea and China. Gardeners appreciate the glossy, dark green foliage that persists through the growing season, offering reliable shade. Despite low maintenance needs, gardeners should note that Alnus × mayrii performs best in cooler climates, showing limitations when grown south of USDA Zone 7.
As a low-maintenance shade tree, the Alder is an unsung hero for difficult sites, including those prone to periodic flooding or featuring poor, infertile soils. Its narrow-oval habit provides vertical interest while its tolerance profile allows it to succeed where many other trees struggle.
Fast Facts
- Plant Family: Betulaceae
- Plant Type: Tree
- Native Range: Korea, China
- Hardiness Zones: USDA Zones 4-7
- Size at Maturity:
- Height: 30-50 ft
- Spread: 20-40 ft
- Bloom Time: March
- Bloom Description: Yellowish-brown (male) Purple (female)
- Sun Exposure: Full sun to part shade
- Water Needs: Medium to wet
- Maintenance Level: Low
How to Grow
Establish the Alnus × mayrii, or Alder, during the dormant season—late fall or early spring—to allow it time to settle before summer heat. Locate it where it receives full sun to light part shade, ensuring the soil offers medium moisture retention, trending towards wet. This tree tolerates occasional flooding, making it superb for riparian zones or rain gardens.
Care for the established Alder is generally very minimal, reflecting its low maintenance rating. While it prefers consistent moisture, it can manage short dry spells once established. Fertilization is rarely needed, especially if planted in appropriately fertile, moist soil. Pruning should be focused primarily on removing dead or damaged wood, typically performed in late winter when the tree is bare.
A critical consideration for success is climate; this hybrid thrives best in cool regions. Avoid planting south of Zone 7, as performance declines significantly in warmer summers where this Alder struggles. If propagation is desired, utilize softwood cuttings taken during the growing season.
Landscape Uses
The Alder excels in functional landscaping roles, especially where water management is a concern. Because it is an uncommon selection in many US landscapes, Alnus × mayrii offers unique character for woodland plantings or as a specimen tree in moist low spots. Its ability to handle wet soil makes it a superior material for building up the edges of retention ponds or naturalized rain gardens.
Consider this tree for structural planting where soil conditions are marginal, such as dry, infertile border areas or sites with heavy clay that retains too much water. While its flowers are insignificant, the overall stature provides effective screening or shade beneath its canopy once mature. Pair the Alder with other moisture-tolerant plants that enjoy similar sun exposure for a cohesive, low-input landscape design.
Standout Features
Flower Qualities
- Insignificant
Noteworthy Characteristics
Alnus × mayrii, commonly called alder, is a medium-sized deciduous tree of the birch family that typically matures over time to 30-50’ tall with a narrow-oval habit. Parents are Alnus japonica (Japanese alder) and Alnus hirsuta (Manchurian alder). This tree is a naturally occurring hybrid cross which occurs in certain areas of Japan and Manchuria where the growth of its parents coincide. Glossy, finely serrate, ovate-lanceolate, dark green leaves (to 3-4” long) are pale green beneath. No appreciable fall color. Flowers are monoecious, appearing in separate male and female catkins (catkins are aggregates of individual flowers in a single structure). Pendant male catkins in clusters with yellowish-brown flowers and short erect less conspicuous female catkins with purplish flowers bloom in late winter to early spring (March). Female catkins are followed by persistent ellipsoidal fruiting cones (to 1” long) with winged seeds which when ripe are dispursed by wind and water. Fruiting cones somewhat resemble the small true cones of some conifers. This hybrid is most similar to its Alnus japonica parent, except its leaves are broader with acute (not acuminate) tips, and it typically grows more vigorously.
Tolerances
- Erosion
- Wet Soil
Potential Problems
The Alnus × mayrii generally exhibits low maintenance, but like many members of the Betulaceae family, it can be susceptible to common fungal and insect issues. Potential disease problems include leaf curl, powdery mildew, rust, and canker, which often become more prevalent during extended periods of high humidity or stress. Monitor the foliage closely in spring and summer for these signs.
To combat potential insect pressure, keep an eye out for aphids, flea beetles, mealybugs, psyllids, and lace bugs. Maintaining diligent cultural practices, such as ensuring good air circulation and appropriate watering, can mitigate many disease outbreaks. Promptly remove and dispose of heavily infected leaves to reduce the spread of rust or mildew spores for the following season.
Frequently Asked Questions
What hardiness zones is Alder suitable for?
The Alder ($Alnus \times mayrii$) is reliably hardy in USDA Zones 4 through 7.
How large does Alnus × mayrii grow?
This medium-sized tree typically matures to a height between 30 and 50 feet, with a spread ranging from 20 to 40 feet wide.
What sun exposure does Alnus × mayrii need?
It performs best when provided with Full sun to part shade conditions, adapting well to slightly dappled light throughout the day.
When does Alder bloom?
Bloom time for the Alder is in March, featuring drooping yellowish-brown male catkins and smaller, erect purplish female catkins.
Conclusion
The Alnus × mayrii offers exceptional value to gardeners seeking hardy, low-effort screening or shade, especially in damp or challenging locations. This tough Alder hybrid brings structure and resilient foliage to sites often deemed unplantable elsewhere. Before incorporating this tree into your design, confirm that your planting site falls within USDA Zones 4-7 and provides the necessary medium to wet soil conditions.
Propagation Tips
Propagating Alnus × mayrii is most successfully achieved through softwood cuttings, which should be taken during the active growth period of late spring or early summer. Select healthy, non-flowering shoots that are slightly pliable but snap when bent. Treating the base of the cutting with rooting hormone significantly increases the success rate before placing them in a well-draining, light medium, such as a peat and perlite mix.
Maintaining high humidity is key to encouraging root development on these Alder cuttings. Placing them under mist or in a humidity dome helps prevent desiccation while the plant focuses energy on establishing new roots. Once roots have developed, usually evidenced by new top growth, the small trees can be carefully transplanted into larger containers to grow on before final placement.
Companion Planting for Wet Sites
When designing a landscape around the adaptable Alnus × mayrii, focus on other plants that share its preference for moist or wet soil, particularly in full sun to part shade. Good partners include various moisture-loving shrubs like Swamp Rose (Rosa palustris) or shrubs in the Ilex genus that tolerate wet feet. These companions will unify the planting scheme while benefiting from the shade offered by the mature Alder.
For groundcovers or understory plants below the growing Alnus × mayrii, consider moisture-loving perennials such as Blue Flag Iris (Iris versicolor) or robust ferns like the Ostrich Fern (Matteuccia struthiopteris). Because this Alder is recommended for difficult sites, selecting native wetland species specific to your region, assuming they meet the hardiness zone criteria, will further enhance the ecological value of the planting.
