Satsuki Azalea bonsai

Satsuki Azalea Bonsai Care

Rhododendron indicum

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Zones 7 to 8, outdoor only. Satsuki azaleas are Japanese garden azaleas, bred there for at least 500 years.

Ericaceae (the blueberry family) · Evergreen to semi-evergreen flowering shrub; outdoor bonsai

At a glance

Type
Broadleaf evergreen
Leaves
Evergreen
USDA zones
7 to 8
Indoor or outdoor
Outdoor
Growth rate
Slow
Buds on old wood
Yes
Bonsai popularity
Tier 1

Close-up photo reference

Compare your tree against these to confirm the species and spot problems early.

Satsuki Azalea in flower
Flower, Daderot · CC0

Satsuki Azalea quick reference

USDA zones7 to 8 in the ground [2] [3]; no source gives zones for a potted tree, so protect it in frost (see Climate) [11]
Indoor / outdoorOutdoor only: outdoors [11]; under glass outside in winter, never brought into the house [12]
LightSun with midday summer shade [11]; Bonsai4Me prefers partial shade [12] (see Light)
WaterConstantly moist: never let it dry out, never keep it soggy [11] [3]
SoilLime-free; pure kanuma is the usual choice [11] [14]
RepotEvery two years [11]; Bonsai4Me repots yearly after flowering [12]
FrostProtect a potted tree below 23°F (-5°C) [11]; Bonsai Mirai warns of damage from long spells below 28°F (-2°C) [13]
Mature height2 to 3 ft in the ground [2]; RHS gives 1.6 to 3.3 ft (0.5 to 1 m) [4]
Growth rateSlow [2] [5]
Season of interestFlowers from mid-May into June [5] [3]; small glossy leaves that often redden in autumn [4]
Leaf reductionNot rated by the sources we checked
Main risksMain risks, not ranked by any source: root rot in wet soil [7] [11], drying out [11] [14], frost on a potted tree [12] [13]

Overview & Character

Satsuki azaleas are Japanese garden azaleas, bred there for at least 500 years [5]. Kew accepts Rhododendron indicum as the species name, in the family Ericaceae [1]; NC State calls the species southern Indian azalea and describes it as evergreen to semi-evergreen [2]. But Satsuki are hybrids: the Azalea Society of America says the first were probably natural crosses of R. indicum and R. tamurae [5], while Bonsai4Me says they were bred mainly from R. indicum and R. simsii [12]. The name refers to the fifth month of the old lunar calendar, when they bloom [15].

They flower late, from mid-May and into June [5] (Bonsai4Me, writing in the UK, says summer [12]), and there are thousands of named varieties [15]. The full range of color patterns can show on a single plant, and the mix changes from year to year [5]. Most are compact, twiggy and slow growing [5], which suits bonsai.

This is not an easy tree. Bonsai Empire notes that azalea bonsai dry out more readily than many other species [11], and Bonsai Mirai finds that the more hybridized cultivars become more delicate, finicky and short-lived [13]. Azaleas are also toxic to pets (see Toxicity) [10].

Identification

Foliage. Evergreen or semi-evergreen [2] [4], with small glossy green leaves that often turn red or purple in autumn [4]. Leaves are narrow and lance-shaped with finely toothed margins [2], and Satsuki leaf length runs from about 1/2 in to 2 in [5].

Bark & trunk. The wood is brittle [11]. None of the sources we checked describes the bark.

Growth habit / form. A small, dense shrub [2].

Flowers / fruit. Funnel-shaped flowers with a corolla 1 to 2 in across [2]. The wild species is usually red, and cultivars vary greatly [3]. The fruit is a dry capsule that splits into five parts [2].

Look-alikes & how to tell them apart: Kurume azaleas (Rhododendron obtusum hybrids [11]; Bonsai Empire and Bonsai4Me also name R. kaempferi and R. kiusianum [11] [12]) are the other common azalea bonsai; they have smaller leaves and more compact growth [11] and bloom earlier, in spring, with many very small flowers [12]. Satsuki bloom later [5] with funnel-shaped flowers that vary widely in size [12].

Climate & USDA Zone

The species is listed for USDA zones 7a to 8b by NC State [2] and zones 7 to 8 by the Chicago Botanic Garden [3]. Those are figures for plants in the ground. The Azalea Society of America says most Satsuki garden plants are hardy to 0°F (-18°C), and a few to -10°F (-23°C) [5].

A tree in a pot is far more exposed, and the bonsai sources set higher limits. Bonsai Empire protects mature azaleas below 23°F (-5°C) [11]. Bonsai Mirai warns that long spells below 28°F (-2°C) can cost branches and damage the trunk [13]. Bonsai4Me calls Satsuki relatively frost-tender and keeps them under glass outside from the start of winter, never indoors [12].

Light

The sources differ. Bonsai Empire likes a sunny spot with shade in the hottest part of a summer day [11]. Bonsai Mirai wants full sun in spring and fall for strong flower buds, shade cloth above 85°F (29°C), and notes that some cultivars tolerate partial or full shade [13]. Bonsai4Me says strong sun fades the flowers and uses partial shade or dappled light [12]. The Azalea Society of America shields Satsuki from afternoon sun [5]. In flower, keep the tree out of rain and hot sun so the blooms last longer [11].

Watering

Constantly moist, never soggy. Azalea bonsai must not dry out, yet they dislike permanent wetness [11]. They recover poorly from drought [11], and Bonsai Tonight warns that roots can die back after a single hot day without enough water [14]. If the root ball does dry out, dunk it in a bowl of water until it is soaked [11].

Hard tap water is not suitable; use rainwater, rain mixed with tap water, or filtered water [11]. In hard-water areas Bonsai4Me uses rainwater only, so lime does not build up [12].

Soil & Root Care

Satsuki need lime-free, acidic soil [11] [12]. Pure kanuma is a good azalea soil [11], and Bonsai Tonight calls 100% kanuma topped with moss the standard mix [14]. Bonsai Mirai uses kanuma particles of 1/8 to 1/4 in (3 to 6 mm) [13]. For garden azaleas, Clemson gives pH 4.5 to 6.0 [6].

Repotting advice varies. Bonsai Empire repots every two years, in spring or after flowering, and cuts the thin, matted roots with great care [11]. Bonsai4Me repots every year as soon as flowering ends, or when roots fill the pot [12]. Bonsai Mirai repots after flowering, usually in late spring, and avoids winter [13].

Feeding

Feed with an azalea or rhododendron fertilizer through the growing season [11]. Bonsai Empire stops or halves the dose while the tree is in flower [11]. Bonsai4Me feeds every two weeks in spring until flowering, not at all during flowering, and monthly afterward with a fertilizer for acid-loving plants [12]. Bonsai Mirai feeds organic fertilizer moderately, since heavy feeding can lead to root rot [13].

Pruning & Styling

Right after flowering, cut or pinch off the wilted flowers and their seed parts [11]. Prune too late and there will be few or no flowers the next year [11]; on garden azaleas, Clemson notes next year's buds form in midsummer [6]. Bonsai4Me deadheads as flowers fade, then prunes and pinches secondary branches until mid-summer [12].

Azaleas take strong pruning well and will shoot even from branches with no leaves left [11], though Bonsai Empire's FAQ adds that regrowth from bare branches can be limited [11]. Bonsai4Me finds that a tree in good health cut back to a stump after flowering buds back freely, but never two years running [12]. Only work on a healthy, vigorous tree [14].

The wood is brittle, so wire and bend with great care [11]. Bonsai4Me finds Satsuki suit every style except formal broom [12].

Seasonal Calendar

Care calendar by month

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

Propagation & Cuttings

Ease: Many common cultivars root easily and quickly [11]. Best methods: cuttings [11] [13]; layering [12].

Bonsai Empire takes cuttings in spring and summer [11]. Bonsai4Me roots softwood cuttings in early summer and air layers or ground layers in early summer after flowering [12].

Pests

Bonsai Empire says azaleas are not often troubled by pests, but low humidity favors spider mites, and vine weevil grubs badly damage the roots [11]. Azalea lace bug feeds under the leaves and causes white stippling on older leaves [8], with black or brownish, tar-like spots underneath [8] [9]. Plants in full sun or under drought stress suffer more [9]. Treat the leaf undersides; insecticidal soap may need repeating about every 2 weeks [9].

Aphids, scale, thrips and whitefly also attack azaleas [2]. Never spray open flowers, which makes them wilt and drop [12].

Disease, Fungus & Infection

Root rot from a fungus follows wet, compacted soil [11]. Phytophthora is a water mold, and a wilting plant is usually the first sign [7]. Petal blight starts as tiny freckle-like spots on the petals; pick off and destroy infected flowers [7]. Leaf gall distorts leaves and buds in April and May, and the galls later turn white and powdery; pick them off [7]. Wetness encourages it, most often on red and purple flowered cultivars [11].

Most Common Causes of Death

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

Toxicity, Safety & Handling

The ASPCA lists azaleas (Rhododendron species) as toxic to dogs, cats and horses; the toxin is grayanotoxin [10]. Signs include vomiting (not in horses), diarrhea, weakness and heart failure [10]. NC State rates the risk to people as low, saying moderate amounts of nectar or leaves pose little hazard [2], and the RHS says the plant is harmful if eaten [4].

Sources

  1. Kew Plants of the World Online: Rhododendron indicum
  2. NC State Extension Plant Toolbox: Rhododendron indicum
  3. Chicago Botanic Garden Plant Finder: Rhododendron indicum, Satsuki azalea
  4. Royal Horticultural Society: Rhododendron indicum (EA)
  5. Azalea Society of America: Satsuki Azaleas
  6. Clemson Cooperative Extension HGIC: Azalea Care
  7. Clemson Cooperative Extension HGIC: Azalea and Rhododendron Diseases
  8. University of Georgia Extension: Azalea Lace Bug
  9. Washington State University HortSense: Azalea lace bug
  10. ASPCA Animal Poison Control: Azalea
  11. Bonsai Empire: Azalea bonsai care
  12. Bonsai4Me: Rhododendron species, Azalea bonsai
  13. Bonsai Mirai: Satsuki Azalea Bonsai
  14. Bonsai Tonight: Top 5 tips for keeping azalea bonsai healthy
  15. Wikipedia: Satsuki azalea

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