Japanese Maple bonsai, a reference image of the species; there is no photograph of Mikawa Yatsubusa Japanese Maple itself yet

Mikawa Yatsubusa Japanese Maple Bonsai Care

Acer palmatum 'Mikawa-yatsubusa'

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Zones 5 to 9, outdoor only. 'Mikawa-yatsubusa' is a dwarf Japanese maple whose buds and leaf nodes sit very close together.

Sapindaceae (the soapberry family) · Deciduous broadleaf tree; outdoor bonsai, a dwarf cultivar of Japanese maple

A cultivar of Japanese Maple.

At a glance

Type
Deciduous
Leaves
Deciduous
USDA zones
5 to 9
Indoor or outdoor
Outdoor
Growth rate
Slow
Bonsai popularity
Tier 1

Mikawa Yatsubusa Japanese Maple quick reference

USDA zones5 to 9 in the ground, per NC State [2] and Maple Ridge Nursery [4]; Iseli and World Plants list only the cold end, zone 5 [3] [6]
Indoor / outdoorOutdoor only, all year [12]
LightA sunny, airy place [12]; dappled shade in hot weather [13]; indirect light once temperatures reach 85°F (29°C) [12]
WaterEvenly moist: water daily in the growing season; it must not dry out completely [12]
SoilWell-drained mix such as akadama with pumice and lava rock [12]; neutral to slightly acidic [12]
RepotEvery two years [12], in spring as the buds start to swell [13]
FrostFrost hardy as a bonsai, but protect it below 15°F (-10°C) [12]; young leaves are frost sensitive [14]
Mature heightA dwarf: 4 to 6 ft (1.2 to 1.8 m) tall and about 4 ft (1.2 m) wide [2]; the RHS says about 3.3 to 3.9 ft (1 to 1.2 m), in its 3.3 to 4.9 ft (1 to 1.5 m) size band [1]; landscape sizes, not bonsai sizes
Growth rateSlow [1] [2]; Iseli gives 3 to 6 in (8 to 15 cm) a year [3]
Season of interestSpring leaves pale yellow-green with red tips and margins [3]; orange, gold and red in fall [1]; green bark in winter [1]
Leaf reductionLeaf pruning brings a second, often finer flush [12]; not rated by the sources we checked
Main risksMain risks, not ranked by any source: verticillium wilt, which cannot be treated and spreads on tools [12]; drying out, which damages fine roots [12]

Overview & Character

'Mikawa-yatsubusa' is a dwarf Japanese maple whose buds and leaf nodes sit very close together [4], so the leaves overlap in layers: shingles to Iseli [3], roof tiles to a University of Washington sheet [7]. It grows slowly [1] [2] and stays small and compact, with a tree-like habit [2] [5]. Maple Ridge Nursery says it was found in the 1970s in the Tokai region of Japan and is named for the old Mikawa province [4].

NC State notes it is often used for bonsai [2], and Leafland calls it a great choice for bonsai [5]. The catch: the leaves are not miniature: 2 to 5 in (5 to 13 cm) in NC State's description, 3 to 6 in (8 to 15 cm) in its attribute list [2], and one grower's notes say they stay large even after full defoliation [8]. Its care follows Japanese maple: the care sections on this page are inherited from the Japanese maple guide.

Identification

Leaves. The RHS counts 5 or 7 lobes [1]; NC State says 5 to 9, on red leafstalks [2]. They lie flat and close [4], so little stem shows between them [10].

Color. New leaves open yellow-green [1] [2], often edged red [3], then turn medium green in summer [2] and darker in shade [4]. Sources differ on fall color: yellow-gold (NC State [2]), orange to red (Maple Ridge [4]), or orange, gold and red (RHS [1]).

Size. Estimates differ: 4 to 6 ft (1.2 to 1.8 m) at 10 years [4], 6.6 ft (2 m) at 10 years [5], 5 to 6 ft (1.5 to 1.8 m) after 15 years [7].

Look-alikes. UBC Botanical Garden forum members say 'Sekka-yatsubusa' differs in habit and leaf shape, Mikawa's lobes being much longer [11].

Climate & USDA Zone

Japanese maple is hardy in USDA zones 5 to 8 [15]; not all cultivars are fully hardy in zone 5, and some need winter protection [15]. As a bonsai it is frost hardy, but below 15°F (-10°C) it should go into a cold frame or similar shelter [12]; a UK club gives the same figure as the limit most Japanese maples can take [13]. Young spring leaves are sensitive to frost, and late frosts can damage them [14]. After repotting, cold is the main threat: Bonsai Tonight keeps freshly repotted trees in a workshop or garage when it turns cold [16].

Heat is the other limit. At 85°F (29°C) and above, move the tree into indirect light [12]; too much sun, wind or drought scorches the leaves [14].

Light

In the landscape it does best in dappled or partial shade, because direct sun can scorch the leaves in summer heat [17]; the Morton Arboretum suggests 4 to 6 hours of light a day [15]. Too much shade slows growth and turns purple leaves greener [17]. Bonsai do well in a sunny, airy place [12]. A healthy tree tolerates full sun but may prefer dappled shade in hot weather [13].

Watering

Evenly moist, never dry. Water a bonsai daily in the growing season and never let the soil dry out completely [12]. In the ground it does best with a consistent supply of water [15]. The mix still has to drain: poorly draining soil or overwatering can cause root rot [13]. Avoid calcareous (hard) water, since the species prefers a neutral or slightly acidic pH [12]. In winter, take care not to overwater [13].

Soil & Root Care

Use a well-drained mix such as akadama with pumice and lava rock [12]; for one forest planting Bonsai Tonight used roughly 65 percent akadama and 35 percent pumice [18]. In the ground it prefers well-drained, slightly acidic soil that stays evenly moist and is rich in organic matter [17].

Repot every two years [12], in spring as the buds start to swell [13]; Bonsai Tonight expected one established forest planting to go two to three years before its next repot [18]. The strong roots fill the pot quickly, so prune them at repotting [12]. Afterward, protect the tree from cold [16], and start feeding a few weeks later, once it has rooted in [16].

Feeding

Feed while the tree is actively growing and ease off toward the end of summer [13]. Solid organic fertilizers supply all the micronutrients and act slowly and gently [12]; a young tree can also get liquid fertilizer once a week [12]. Avoid high-nitrogen fertilizers, which make large leaves and long internodes [12].

Pruning & Styling

Shoots extend very little each year, so one grower advises minimal pruning while the trunk and height develop, and warns that hard cutting early can cost years [8]. Reported growth runs from about 2 in (5 cm) a year to 9 to 12 in (23 to 30 cm) a season on some shoots [9].

One grower's notes say to remove the under leaves and keep the outer ones, or the tree stops growing for the year, and to thin the upper and outer growth hard, or the interior loses its fine branching [8]. The same notes say to grow it large first, trunk and height before branches [8]; the same notes put a finished tree at 24 in (61 cm) or more, not shohin size [8].

Several growers in one forum thread mention grafted plants [9]. One Bonsai Nut poster says the graft will need to be dealt with on a bonsai, and suggests air layering just above it [8].

Seasonal Calendar

Care calendar by month

Northern Hemisphere. In the Southern Hemisphere, shift every month by six.

Propagation & Cuttings

The RHS lists layering in fall, grafting in late winter, or softwood cuttings [1]. Growers disagree on cuttings: Bonsai Nut posters report that cuttings failed and that the cultivar rarely roots from them, while air layering and grafting work [8]. World Plants calls it difficult to graft [6].

Pests

Aphids, sap-sucking insects, appear on spring growth [12]; scale, maple worms, leafrollers and leafhoppers are occasional pests [14]. Horticultural oil sprays usually control scale [19]. Borers are a sign that the tree is not growing well [19]. Japanese beetles attack Japanese maple very frequently [20].

Disease, Fungus & Infection

Verticillium wilt enters through the roots and spreads through the plant [21]. Individual branches suddenly wilt and die [22], often on one side of the tree only [23], and brown or green streaks show in the sapwood just under the bark [22]. There is no cure [22] [12]; Penn State notes that some trees do recover [23]. Clean pruning tools between cuts for at least 30 seconds in a 10 percent bleach solution [22], and keep in mind that mulch and fallen leaves can carry the fungus [22].

Anthracnose (brown lesions on the leaves), powdery mildew, leaf spot and leaf scorch also trouble Japanese maples [17]. Scorch comes from too much sun, wind or drought [14].

Most Common Causes of Death

No source we checked ranks these. They are the main risks the sources describe, in no particular order:

Sources

  1. RHS: Acer palmatum 'Mikawa-yatsubusa' (Dw)
  2. NC State Extension Plant Toolbox: Acer palmatum 'Mikawa yatsubusa'
  3. Iseli Nursery: Acer palmatum 'Mikawa Yatsubusa'
  4. Maple Ridge Nursery: Acer palmatum 'Mikawa yatsubusa' Dwarf Japanese Maple
  5. Leafland: Acer palmatum 'Mikawa-yatsubusa' (Japanese Maple)
  6. World Plants: Acer palmatum 'Mikawa-yatsubusa'
  7. University of Washington: Mikawa Yatsubusa memory garden tree sheet
  8. Bonsai Nut forum: Mikawa Yatsubusa advice
  9. UBC Botanical Garden Forums: Mikawa yatsubusa, your growth rate?
  10. UBC Botanical Garden Forums: Acer palmatum 'Mikawa yatsubusa' (photos)
  11. UBC Botanical Garden Forums: Sekka vs Mikawa yatsubusa
  12. Bonsai Empire: Japanese Maple bonsai care
  13. Swindon Bonsai Club: Maples, not just for syrup
  14. NC State Extension Plant Toolbox: Acer palmatum
  15. The Morton Arboretum: Japanese maple
  16. Bonsai Tonight: You just finished repotting, now what?
  17. Clemson Cooperative Extension HGIC: Maple
  18. Bonsai Tonight: Repotting a Japanese maple forest planting
  19. NC State Extension, Currituck County Center: Japanese Maple
  20. University of Maine Cooperative Extension: Plant Tolerance of Japanese Beetles
  21. Washington State University Hortsense: Maple, Verticillium wilt
  22. University of Wisconsin Extension: Verticillium wilt
  23. Penn State Extension: Maple Diseases
  24. Oregon State University Landscape Plants: Acer palmatum

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