Japanese Alder (Alnus japonica)

Japanese Alder

Alnus japonica

Its serrated leaves bring soft woodland texture, a quiet anchor for wet soils. Deciduous tree; common name: Japanese Alder.

Partial sun
2–3/week
Beginner
🌱

Plant Needs

☀️
Sunlight Tolerates full sun to partial shade; thrives in moist, open woodland settings
💧
Watering Keep soil consistently moist; tolerant of standing water and boggy conditions
🌡️
Temperature Hardy to -10°C; adapts to cool temperate to warm temperate climates
🔍

Characteristics

  • Leaf: Oval to oblong, serrated margins, dark green above, paler beneath, 5–12 cm long
  • Flower: Male catkins are pendulous, yellow-brown; female catkins are small, upright, greenish
  • Stem/Bark: Smooth gray-brown bark when young, becoming fissured with age
🛠️

Care Guide

Watering

Keep soil consistently moist; no need to restrict water in wet periods

Fertilization

No regular fertilization needed; optional light feed if soil is poor. Use only diluted, balanced organic feed if necessary

Eggshell powder topdressing:Crush dried eggshells into fine powder; sprinkle lightly on soil surface to boost calcium levels without burning roots
Pruning
  • Remove dead or damaged branches in late winter to maintain structure
  • Thin crowded branches to improve airflow and light penetration
  • Avoid heavy pruning; tree has a naturally upright, symmetrical form
⚠️

Toxicity

Warning: this plant may be toxic.

Pets & Humans

Pets: ASPCA: Non-toxic; no adverse effects reported for cats

Humans: No known toxic effects; safe for human handling and incidental contact

📖

Garden Uses & Culture

Culture: N/A

Usage: Soil stabilization in riparian zones; ornamental shade tree for wet gardens