'O Isami' Japanese Maple: A Striking Full Moon Maple Cultivar

Cultivar Profile: Acer japonicum 'O Isami'

Among the full moon maples (Acer japonicum), 'O Isami' (also spelled 'Oh Isami' or 'Oisami') stands out for its large, deeply lobed leaves that emerge bright green in spring, mature to a rich mid-green, and transform into a spectacular blaze of orange, crimson, and gold in autumn. This cultivar brings the refined elegance of Japanese maples to gardens with slightly more sun tolerance than many palmatum varieties.

Key Characteristics

• Leaf: 7–11 deeply cut lobes, larger than typical A. japonicum; 4–6 inches across.
• Spring color: Fresh yellow-green, often with reddish petioles.
• Summer color: Medium green.
• Fall color: Brilliant orange-red to crimson, one of the most intense of the japonicum cultivars.
• Habit: Upright, spreading small tree; 15–20 ft tall and wide at maturity.
• Hardiness: USDA zones 5–8.

Botanical Background

• Family: Sapindaceae.
• Species: Acer japonicum (Full Moon Maple, Downy Japanese Maple).
• Native range: Japan, Korea, Manchuria.

Growing Requirements

• Light: Part shade ideal; tolerates more sun than A. palmatum if soil moisture is consistent. Morning sun / afternoon shade is perfect.
• Soil: Moist, well-drained, slightly acidic, rich in organic matter.
• Water: Regular, deep watering; avoid drought stress, especially in first years.
• Mulch: 2–3 inch layer of shredded bark or leaf mold to conserve moisture and moderate soil temperature.

Landscape Uses

Superb as a specimen tree in a woodland garden, Asian-themed border, or near a water feature where its reflection doubles the autumn show. Its larger leaves give a bolder texture than most Japanese maples. Pair with ferns, hostas, hakonechloa, and rhododendrons.

Care Notes

• Minimal pruning needed; remove dead or crossing branches in late winter.
• Protect from drying winds, especially in winter.
• Fertilize lightly in early spring with a slow-release, acid-forming fertilizer.