Alder buckthorn (Frangula alnus 'Asplenifolia')

Overview

Frangula alnus ‘Asplenifolia’, commonly known as Alder buckthorn, provides distinctive texture to the landscape with its extremely narrow, glossy green leaves resembling fern pinnae. This upright, spreading deciduous shrub is valued for its relatively low maintenance requirements and tolerance across a wide range of USDA hardiness zones. While the spring flowers are not showy, the subsequent berries that mature from green to red and finally dark purple attract local bird populations.

The cultivar ‘Asplenifolia’ maintains good green color well into autumn, though notable fall color is usually absent. Gardeners appreciate this specific variety for its unique foliage shape, setting it apart from many common landscape shrubs. It adapts well to various soil conditions provided drainage is adequate, making the Alder buckthorn a reliable choice for structure.

Despite its aesthetic and wildlife benefits, gardeners must confirm local invasiveness status before planting Frangula alnus ‘Asplenifolia’, particularly in the Northeast and Midwest of the United States. When sited correctly and given consistent moisture, this shrub offers years of reliable structure and seasonal interest.

Fast Facts

• Plant Family: Rhamnaceae
• Plant Type: Deciduous shrub
• Hardiness Zones: USDA Zones 2-7
• Size at Maturity:
  • Height: 10-12 ft
  • Spread: 6-10 ft
• Bloom Time: May
• Bloom Description: Whitish-green
• Sun Exposure: Full sun to part shade
• Water Needs: Medium
• Maintenance Level: Low

How to Grow

Plant Frangula alnus ‘Asplenifolia’ during the early spring or fall, favoring locations that receive full sun to partial shade. This shrub is quite adaptable regarding soil type but thrives best in average, medium-moisture, well-drained conditions. Ensure the planting site allows for sufficient space, as recommended spacing for hedging is 24–30 inches apart.

Once established, the Alder buckthorn requires a medium water intake, preferring consistent moisture but tolerating general garden conditions due to its adaptability. Fertilization is rarely necessary. Maintenance remains low; however, hedging or shaping can be performed as needed to maintain the desired height and form.

The species exhibits prolific self-seeding, though new seedlings may not genetically match the parent ‘Asplenifolia’ form; therefore, propagation via cuttings is the preferred method for maintaining cultivar purity. Be aware of possible foliage pests like Japanese beetles or scale, and monitor for fungal issues such as leaf spots or rust.

Landscape Uses

The textural contrast offered by Frangula alnus ‘Asplenifolia’ makes it an excellent choice for shrub borders where its fine-textured, narrow foliage can stand out against broadleaf companions. Its height potential (up to 12 feet) allows it to function effectively as a backdrop planting, screening utility areas or providing height definition against fences.

This plant is also suitable for foundational massing or creating informal, structural hedges. When planting in hedges, maintain 24-30 inches between specimens. Due to the attraction birds have to its maturing berries, place the shrub where spent fruit is not a nuisance if planted near patios.

Standout Features

Flower Qualities

• Insignificant

Fruit Qualities

• Showy

Noteworthy Characteristics

Frangula alnus is commonly called alder buckthorn because it is frequently seen in the wild growing in moist soils near alders (genus Alnus). It is also commonly called glossy buckthorn in reference to its glossy leaves. The glossy, oval to obovate, dark green leaves retain their green color well into fall, usually resulting in poor fall color. Insignificant whitish-green flowers appear in axillary clusters in May-June, which attract bees. Flowers are followed by inedible berries that ripen in July, changing from green to red to dark purple as they mature, attracting birds that help spread the seeds. The cultivar ‘Asplenifolia’ is recognizable because its glossy green leaves are unusual, possessing the general appearance of fern pinnae: extremely narrow with irregular margins, sometimes leading to the common name fern-leaf buckthorn.

Tolerances

This information was not provided for this specific cultivar.

Potential Problems

Common pests that may appear on Frangula alnus ‘Asplenifolia’ include Japanese beetles, caterpillars, and scale insects, which can sap the foliage. Root health is also a concern, as nematodes have been known to attack the roots of buckthorns. Gardeners should remain vigilant for common fungal diseases such as cankers, leaf spots, and rust, ensuring good air circulation and appropriate watering practices to minimize outbreaks.

Frequently Asked Questions

What hardiness zones is Alder buckthorn suitable for?

The Frangula alnus ‘Asplenifolia’ is robust, thriving in USDA Hardiness Zones 2 through 7.

How large does Alder buckthorn grow?

This deciduous shrub typically reaches a mature height between 10 and 12 feet tall, spreading 6 to 10 feet wide.

What sun exposure does Frangula alnus ‘Asplenifolia’ need?

For best performance, the Alder buckthorn requires full sun exposure, though it tolerates partial shade well.

When does Alder buckthorn bloom?

Bloom time is generally in May, producing inconspicuous flowers described as whitish-green.

Conclusion

The Alder buckthorn, Frangula alnus ‘Asplenifolia’, provides exceptional textural interest through its unique, narrow foliage and serves as a sturdy, low-maintenance shrub for hedges or borders. Before purchasing, confirm that US Zone 2-7 suitability matches your local climate. Plan to plant during the cooler seasons for the best establishment of this reliable specimen.

Companion Planting

Given the preference of Frangula alnus ‘Asplenifolia’ for medium moisture and adaptability across sun conditions, it pairs well with other robust, easy-care shrubs. Consider placing it near plants that offer contrasting leaf shapes or reliable fall color, since the Alder buckthorn itself is not known for vivid autumn displays. Native options like Aronia melanocarpa (black chokeberry) share cultural needs and offer superior fall foliage.

Wildlife Benefits

The flowering period of Frangula alnus ‘Asplenifolia’ in May is beneficial as the inconspicuous whitish-green flowers are attractive to foraging bees. Furthermore, the plant produces berries that mature over several months, drawing in various bird species eager to consume the developing fruit. Planting this shrub aids biodiversity by providing necessary nectar resources early in the season and late-season food sources for birds.