Culture
Winter hardy to USDA Zones 10-11 where it is best grown on well-drained, medium to strongly acid soils in full sun. Performs well in areas of high rainfall. Propagation is usually from seed.
Noteworthy Characteristics
Acacia koa, commonly known as koa, is a large, fast-growing, evergreen tree of the pea family that is native to the Hawaiian Islands where it typically matures to 50-80’ (occasionally to 100’) tall with a dense broad-spreading crown. It is usually found in mountainous areas at elevations ranging from 300’ to 7000’ on the larger Islands (Kauai, Oahu, Molokai, Maui, Lanai and Hawaii). It is the second most common tree in the Hawaiian Islands.
Mature trees have stiff, dull green, sickle-shaped, evergreen phyllodes (to 6” long and 1” wide) rather than leaves. Phyllodes are modified leaf stems that function as leaves. The true leaves of this tree (each with 12 to 15 paired, twice compound, pea-like leaflets) are only found on juvenile saplings. Pale yellow flowers with globose heads (each to 3/8” in diameter) bloom in axillary racemes over the outer part of the crown. Bloom time depends upon a number of factors including elevation, weather conditions and soil moisture. Flowers may appear year round in some locations or late winter to early summer in others. Flowers give way to thin, flat, seed pods (about 3-7” long and 1” wide) which mature to brown. Each pod contains around 12 seeds.
Koa is the best known timber tree endemic to the Hawaiian Islands. Early Hawaiians made long dugout canoes from the wood of tall trees. Wood is currently used for a variety of other purposes including furniture, cabinets, veneers, wood carvings, musical instruments and picture frames. Timber from this tree is sometimes called Hawaiian mahogany in honor of its decorative wood (beautifully grained in shades of red, golden brown and brown). It is one of the most expensive woods in the world today (low supply translates into high cost). Most commercial harvest of Koa trees is currently limited to the island of Hawaii. Timber cutting, land clearing and introduced pests have contributed to the decline of this species in the Hawaiian Islands.
Genus name come from the Greek name for Acacia arabica.
Specific epithet is a native Hawaiian name meaning bold, brave and fearless.
Problems
No serious insect or disease problem. Koa moth can be destructive. Watch for twig borers, fungi and koa wilt.
Uses
Interesting landscape tree for subtropical areas. Has been successfully grown in a number of California areas.