This past weekend I spent a frosty Hawaiian winter solstice with the Moku Loa chapter of Sierra Club while on an overnight camping trip at Keanakolu cabins along historic Mana Road on the slopes Mauna Kea. By night there were clear skies filled with billions of stars and a bright mohalu crescent moon; by day, several trails yielded endless opportunities to explore the native flora of the cloud forest.
The dominant tree in this area is the majestic koa (Acacia koa), and in these old-growth forests the trees are over a hundred feet high. As you can see in the above photo, many have developed into the twisted wild forms that make bonsai practitioners shiver and sigh with delight.
Abundant and perhaps apropos for the Christmas season was native Hawaiian mistletoe, hulumoa, an unusual, primitive-looking parasitic plant that lives on koa.
Many a suburban gardener would love to plant a koa tree in the backyard, however, seeing these specimens in the cool, misty upland pastures reminded me that dwarf koa, or koai’a, is probably a better choice for our human-inhabited, drier lowland landscapes.
Koai’a (Acacia koaia) looks like koa but has longer seed pods and a lower, more rounded shape only 15 to 25 feet high; it does well in hot, dry areas. Koa roots tend to send out suckers, but koai’a grows more slowly and is not as aggressive. Unlike regular koa, koai’a is drought tolerant and can tolerate a fair amount of wind and salt.
Note how the crescent-shaped koa "leaves" (actually phyllodes) compare with the pink feather-like leaves of nonnative eucalyptus – quite a difference.
Recently I was impressed with some striking specimens of koai’a in the Waimea Nature Center, a native garden maintained by the community and the Waimea Outdoor Circle. These plantings are an excellent example of how to utilize the distinctive look of koa in residential yards and landscaped areas intended for public recreation.
On the internet, there’s lots of info on growing koa and koai’a.
If you’d like an overview on what the University of Hawaii is doing to save our native forests, click here.
To learn how to propagate koa, click here.
Also, here’s a few superb books to consult:
Growing Koa: A Hawaiian Legacy Tree, by Craig Elevitch and Kim Wilkinson
Growing Native Hawaiian Plants, by Heidi Leianuenue Bornhorst