Alnus

Description

Alnus is a genus of deciduous trees and shrubs native to the temperate and subtropical regions of the Northern Hemisphere. The genus includes about 35 species, with the most common being the European alder (Alnus glutinosa) and the speckled alder (Alnus incana).

Taxonomic Information

Appearance

Alnus trees and shrubs typically have simple, toothed leaves that are dark green and glossy on top and paler and hairy underneath. They produce male and female flowers on separate trees, with the male flowers forming in hanging catkins and the female flowers forming in small cones. The trees also produce small, woody fruits that resemble cones.

Care Guide

Alnus trees and shrubs are relatively low-maintenance, but they do require some care to thrive:

• Water: Alnus trees and shrubs prefer moist, well-drained soil and should be watered regularly, especially during dry spells.
• Fertilization: Alnus trees and shrubs benefit from regular fertilization with a balanced fertilizer in the early spring.
• Soil: Alnus trees and shrubs prefer acidic soil and should be planted in a location with a pH between 5.0 and 6.5.
• Sunlight: Alnus trees and shrubs prefer full sun to partial shade.
• Hardiness Zones: Alnus trees and shrubs are hardy in USDA zones 3-9.

Common Pests & Diseases

Alnus trees and shrubs are relatively resistant to pests and diseases, but they can be affected by a few common issues:

• Phytophthora root rot: This fungal disease can cause wilting, yellowing, and dieback of the tree or shrub. It is most common in poorly drained soil.
• Rust: This fungal disease can cause yellow or orange spots on the leaves and cankers on the branches. It is most common in wet weather.
• Alder flea beetle: This insect pest can cause defoliation of the tree or shrub. It is most common in the spring.

Habitat

Alnus trees and shrubs are found in a variety of habitats, including wetlands, riverbanks, and upland forests. They are important components of riparian ecosystems, as they help to stabilize stream banks and provide habitat for wildlife.

Question and Answer

Q: Are Alnus trees and shrubs fast-growing?

A: Yes, Alnus trees and shrubs are known for their fast growth rate, especially in moist soil.

Q: Can Alnus trees and shrubs be used for erosion control?

A: Yes, Alnus trees and shrubs are commonly used for erosion control, as their roots help to stabilize soil along stream banks and other waterways.

Q: Do Alnus trees and shrubs require pruning?

A: Alnus trees and shrubs do not require regular pruning, but they can be pruned to remove dead or damaged branches or to shape the tree or shrub.

Q: Are Alnus trees and shrubs tolerant of pollution?

A: Yes, Alnus trees and shrubs are tolerant of pollution and are often used for phytoremediation of contaminated soil and water.

Related Plants

• Betula (birch)
• Carpinus (hornbeam)
• Corylus (hazel)
• Ostrya (hop hornbeam)

References

• Dirr, M. A. (2009). Manual of woody landscape plants: Their identification, ornamental characteristics, culture, propagation and uses.
• USDA Plants Database: Alnus
• Missouri Botanical Garden: Alnus