Acacia koa
Genus
Acacia
Species
koa
Hawaiian Names with Diacritics
- Koa
Hawaiian Names
- Koa
Common Names
- Koa
Synonyms
- Acacia hawaiiensis
- Acacia heterophylla var. latifolia
- Acacia kauaiensis
- Racosperma kauaiense
- Racosperma koa
Distribution Status
Endemic
Endangered Species Status
No Status
Plant Form / Growth Habit
- Tree
Mature Size, Height
- Tree, Small, 15 to 30
- Tree, Medium, 30 to 50
- Tree, Large, Greater than 50
Mature Size, Width
Koa can have a canopy spread of 40 feet or more.
Life Span
Long lived (Greater than 5 years)
Landscape Uses
- Provides Shade
- Screening
- Specimen Plant
Plant Produces Flowers
Yes
Flower Type
Not Showy
Flower Colors
- Cream
- White
- Yellow
Additional Flower Color Information
Light yellow, cream or white round powder puff flowers.
Blooming Period
- Sporadic
- January
- February
- March
Additional Blooming Period Information
Flowering occurs most heavily from January to March and into May with seeds ripening in August, September and October and persistent year round. [6]
Plant texture
- Medium
- Coarse
Additional Plant Texture Information
Leaves are 2 to over 10 inches long. Koa have sickle-shaped mature "leaves" called phyllodes, which are the main photosynthetic organs. Juvenile leaves, the true leaves, are feathery compounds.
Leaf Colors
- Light Green
- Medium Green
Additional Leaf Color Information
Koa leaves are green to gray green.
Source of Fragrance
No Fragrance
Additional Pest & Disease Information
Koa is known to attract aphids and whiteflies. Chinese rose beetles, an unidentified small gray weevil, mealybugs and a stem boring grub are also known to infest plant. A serious pest is the black twig borer.
Since koa forms a symbiotic relationship with bacteria in the roots for the nitrogen-fixing process, it is recommended that pesticides not be used around the root area.
Fertilizer
Lightly fertilize seedlings 2 or 3 weeks after secondary growth. Since koa are nitrogen fixing trees, additional nitrogen is usually not necessary.
Pruning Information
Koa should not be pruned if it can be avoided. Lower branches do self prune. If pruning is needed, it should be minimal, done properly, and without excessive injury to the tree.
Water Requirements
Dry
Additional Water Information
Water once a month during dry months, more often for "coastal" trees.
Soil must be well drained
Yes
Light Conditions
- Full sun
- Partial sun
Additional Lighting Information
Koa does best in full sun.
Spacing Information
Trees should be spaced 30 to 40 ft. apart.
Tolerances
- Drought
- Wind
Soils
- Clay
- Cinder
- Organic
Limitations
Surface roots are easily damaged and so does not do well in high foot traffic areas. Koa are not tolerant of salt, constant waterlogged soils, or shade. [1]
Natural Zones
- 150 to 1000, 0 to 50
- 150 to 1000, 50 to 100
- 1000 to 1999, 0 to 50
- 1000 to 1999, 50 to 100
- 2000 to 2999, 0 to 50
- 2000 to 2999, 50 to 100
- 3000 to 3999, 0 to 50
- 3000 to 3999, 50 to 100
- 4000 to 4999, 0 to 50
- 4000 to 4999, 50 to 100
Natural Range
- Kauaʻi
- Oʻahu
- Molokaʻi
- Lānaʻi
- Maui
- Hawaiʻi
Additional Growth Environment Information
Though not as common as in the past, koa is still easily found in suitable habitat often a dominant component of native and alien mixed forests. Koa grows in dry to moist forests from 300 to 7,000 feet, occasionally as low as 80 feet and rarely as high as 8,000 feet. [1]
While koa can grow to heights of over 100 feet in their natural undisturbed environment, it would take many decades, if ever, to reach such heights in the urban landscape. They are more likely to grow to about 20 to 30 feet in the landscape at low elevations. [Rick Barboza, Hui Kū Maoli Ola]
Special Notes and Information
Koa belongs to the third largest plant family, the Pea or Legume family (Fabaceae). There are two endemic species of Acacia in the Hawaiian Islands: Acacia koa and A. koaia.
Koa resemble their smaller cousins koaiʻa, but there are some significant differences. (See Acacia koaia "Special Notes and Information")
Koa varies greatly from one location to another. For this reason and others, it is vital that koa or any other native plants from nurseries are never planted out in the wild. This will ensure genetic variability and alleviate unforeseen problems.
Early Hawaiian Use
The name koa means brave, bold, fearless. Early Hawaiians carefully selected large koa for war canoes (waʻa) or those used on long journeys. Koa wood was also used in constructing house (hale), spears, paddles, kahili handles, and short surfboards. [1,3] The bark was used as dye to stain kapa a red color. [1]
While there were many uses for koa, it was never used for eating receptacles because the resin, which could not be removed, would leave a bad taste to foods. [2]
Modern Use
Today, the wood is still very much prized in wood craft and is high in demand being one of the most expensive woods in the world. [1] Koa is also a tonewood and used in modern musical instruments as ʻukulele, acoustic guitars such as used country music artist Taylor Swift, some electric guitars, and Weissenborn-style Hawaiian steel or lap guitars. [5]
Dyes can still be made from koa bark. The dye colors will range from light to very dark (blackish) according to the mordant (dye setting metal substance) used on the fabric. [4]
Landscape Use
Koa are fast growing trees, especially when young, and can reach impressive heights in several decades in upper elevation landscapes. Though koa can grow at lower elevations, some varieties may succumb to diseases after a decade of growth. Since there is so much variety in koa habit from shrubby, multi-branched forms to tall straight trees, it is good to inquire of the source so as to suit your landscaping needs.
Growth is in virtue of symbiosis with special bacteria called rhizobia that live associated with the roots. The bacteria convert, or fix, nitrogen from the air into usable nitrogen fertilizer for plants. The leaves, flowers and branches also provide nitrogen for understory and plants in the area. Koa inoculated with rhizobia tend to be more vigorous trees. [1]
Additional References
[1] "Growing Koa" by Kim M. Wilkinson, pages 5, 7, 11-12, 35-36.
[2] "Plants in Hawaiian Culture" by Beatrice H. Krauss, pages 22, 52, 65.
[3] "Arts and Crafts of Hawaii" by Te Rangi Hiroa (Sir Peter H. Buck), page 384.
[4] "Hawaii Dye Plants and Dye Recipes" by Val Frieling Krohn-Ching, pages 77, 136.
[5] http://en.wikipedia.org/wiki/Acacia_koa [Accessed 10/7/09]
[6] "Plants of the Canoe People" by W. Arthur Whistler, page 27.
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