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Acacia koa

leaf Main Plant Information

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

leaf Plant Characteristics

Distribution Status

Endemic

Endangered Species Status

No Status

Plant Form / Growth Habit

  • Tree

Mature Size, Height (in feet)

  • 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

Additional Landscape Use Information

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]

Source of Fragrance

  • No Fragrance

Plant Produces Flowers

Yes

leaf Flower Characteristics

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 and Fruiting 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]

leaf Leaf Characteristics

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.

leaf Pests and Diseases

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.

leaf Growth Requirements

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]

leaf Environmental Information

Natural Range

  • Kauaʻi
  • Oʻahu
  • Molokaʻi
  • Lānaʻi
  • Maui
  • Hawaiʻi

Natural Zones (Elevation in feet, Rainfall in inches)

  • 150 to 1000, 0 to 50 (Dry)
  • 150 to 1000, 50 to 100 (Mesic)
  • 1000 to 1999, 0 to 50 (Dry)
  • 1000 to 1999, 50 to 100 (Mesic)
  • 2000 to 2999, 0 to 50 (Dry)
  • 2000 to 2999, 50 to 100 (Mesic)
  • 3000 to 3999, 0 to 50 (Dry)
  • 3000 to 3999, 50 to 100 (Mesic)
  • 4000 to 4999, 0 to 50 (Dry)
  • 4000 to 4999, 50 to 100 (Mesic)

Habitat

  • Terrestrial

Additional Habitat 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]

leaf Special Features and Information

General 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" and also "warrior, fighter." 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]

Medicinally, koa leaves were placed under a pile of lau hala mats if a person had been in a sick bed for a long time. Leaves were placed on top and spread evenly over the mat to make to person comfortable.The heat that came from the body and the leaves would make the person sweat. [7,9] Someone would wipe the sweat from the person as they fell asleep. This was almost always used for patients with a fever. [7] Young children under a year old who had become weak were given a mixture of koa leaf ash and other plants and applied inside the mouth. [7,9] The bark was applied to pūhō (abscess, burst sore, ulcer), ʻalaʻala (scar, sore perhaps tuberculosis adentis), kaokao (syphilis), leprosy (maʻi lēpela), ʻeha māui (sore bruises), and haki (broken bones). [10]

Koa leaves were also used in lei making. [8]

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 such 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]

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.

[7] "Native Plants Used as Medicine in Hawaii" by Beatrice Krauss, page 20.

[8] "Nā Lei Makamae--The Treasured Lei" by Marie A. McDonald & Paul R. Weissich, page 42.

[9] "Hawaiian Herbs of Medicinal Value, by D.M. Kaʻaiakamanu & J.K. Akina, page 46.

[10] "Native Hawaiian Medicine--Volume III" by The Rev. Kaluna M. Kaʻaiakamanu, pages 62-63.

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" and also "warrior, fighter." 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]

Medicinally, koa leaves were placed under a pile of lau hala mats if a person had been in a sick bed for a long time. Leaves were placed on top and spread evenly over the mat to make to person comfortable.The heat that came from the body and the leaves would make the person sweat. [7,9] Someone would wipe the sweat from the person as they fell asleep. This was almost always used for patients with a fever. [7] Young children under a year old who had become weak were given a mixture of koa leaf ash and other plants and applied inside the mouth. [7,9] The bark was applied to pūhō (abscess, burst sore, ulcer), ʻalaʻala (scar, sore perhaps tuberculosis adentis), kaokao (syphilis), leprosy (maʻi lēpela), ʻeha māui (sore bruises), and haki (broken bones). [10]

Koa leaves were also used in lei making. [8]

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 such 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]

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