Arakawa maple

Arakawa (literally "rough river" or "rough bark") is the Japanese maple cultivar prized above all others for bark character. The young bark is smooth and standard for the species, but as the tree ages, the bark develops increasingly pronounced corky fissures, vertical splits, and plated character that gives the trunk a quality of weathered age unmatched by any other palmatum cultivar. A 30-year-old Arakawa bonsai has bark that looks closer to a century-old oak than a maple.

The trade-off is that bark development takes time and requires the trunk to thicken to reveal its character. A young Arakawa tree with a slender trunk looks like any other Japanese maple — the cultivar's defining feature only emerges as the trunk thickens, typically after 15–20 years of growth. For this reason, Arakawa material is most often purchased as mature specimens with the bark character already established, or developed slowly in growing beds before potting up.

Foliage is standard palmatum-like — five-lobed leaves typically 5–7cm, green through summer, transitioning to gold-orange-red in autumn. The cultivar grows vigorously when established, with internode length more like base palmatum than the compact Shishigashira or Kiyohime. This vigour can be used to advantage when growing on for trunk and bark development.

A subtle point about Arakawa: aggressive pruning of major branches removes the bark character on those sections. Plan major structural work early in development, before the corky bark establishes, then let the bark develop on the established structure rather than continuing to remove major sections.

Daily through the growing season. Standard Japanese maple watering — twice daily in summer heat for trees in shallow pots. The cultivar's slightly vigorous habit means it tolerates inconsistent watering marginally better than dwarf cultivars but still demands consistent moisture.

In winter, regular but reduced watering. Use rainwater where possible.

Weekly half-strength liquid feed from late April through to mid-September. Slow-release organic pellets in spring and early summer.

The cultivar tolerates slightly heavier feeding than Shishigashira or Kiyohime while in trunk-development phase — useful for building girth that will eventually show off the bark character. Reduce feeding once the desired trunk size has been achieved and the tree is in refinement.

Stop feeding by mid-September.

Free-draining and slightly acidic. Standard Japanese maple substrate.

Repot every 2–3 years on young trees, every 3–4 on mature specimens with established bark. The window is mid-February through to early April. Repot as buds swell.

Arakawa tolerates moderate root work — up to a third of the root mass. The cultivar recovers reasonably quickly.

A specific consideration: avoid scraping or damaging the bark during repotting handling. The corky bark on mature trees is fragile and damage shows for years.

Standard Japanese maple technique with two specific Arakawa considerations.

First, plan major structural pruning early. Once corky bark has established on a branch (typically after 10+ years), removing the branch eliminates that bark and the resulting cut, even if it heals cleanly, will look conspicuously smooth against the surrounding aged bark for decades. Major reductions should happen in the first decade of development, then leave the established structure intact while developing ramification.

Second, the bark character extends along the developing wood. Branches that are kept and allowed to thicken will develop bark character along their length. Branches that are repeatedly removed and regrown won't.

Beyond these considerations, standard maple pruning applies. Through the growing season, allow new shoots to extend to 4–5 leaves then cut back to 2. Pinch every two to three weeks. Structural work in late winter.

Defoliation works well on healthy trees and produces refined second-flush foliage. The cultivar can take annual defoliation on vigorous specimens.

Wire after leaves harden in early summer or on bare branches in winter.

A critical Arakawa wiring consideration: wire bites in dramatically faster on corky bark than smooth bark, and wire scars are essentially permanent on the aged bark surface. Apply very loosely, check weekly during active growth, and remove and re-apply often rather than leaving wire on for extended periods. Some growers avoid wire entirely on mature Arakawa specimens and rely exclusively on directional pruning.

Aluminium for almost all work; copper only for major structural branches on younger material before bark character has developed.

Informal upright is the classic Arakawa style — the cultivar's natural habit and the corky bark suit this form ideally. Twin-trunk and clump styles work well. Substantial vertical trunks that showcase the developed bark character are particularly fine.

Cascade and semi-cascade are uncommon but possible on suitable material. Forest plantings work but are less effective — the bark character is the cultivar's main asset and individual trunks display it better than groups.

The bark is the main visual feature — styling should ensure the trunk is clearly visible from typical viewing angles rather than hidden behind dense foliage.

Hardy across most of the UK with no protection needed in normal winters. The mature corky bark provides better insulation against winter cold than smooth bark — established Arakawa specimens are slightly more cold-tolerant than young plants of the same cultivar.

The main winter concern is wind on the bark — exposed positions in strong wind can desiccate older corky bark and cause flaking. Provide some shelter in exposed gardens.

Never bring indoors.

Always grafted onto Acer palmatum rootstock. Cuttings rarely succeed and don't reliably reproduce the bark character. Air layering of established Arakawa branches can produce own-root specimens but the bark character takes years to redevelop on the resulting tree.

Generally healthy. Inherits base palmatum's vulnerabilities but the established bark provides some protection against borers and trunk issues.