Acacia koa

koa
Iconic Hawaiian tree renowned for its grand form and glowing hardwood. Large, long-lived forest tree grows into a wide oak-like or umbrella form. A rare treasure.
height 30–60ft
width 15–35ft
tolerates Cool Summers, Drought, Fog
water
needs		 Low – Moderate
water
info		 For the first three years after it’s planted, this acacia should be watered deeply but infrequently (when the top three inches of soil or so have dried). After that, it will want deep irrigation every month or so during the dry season. Use drippers, emitters or a slow stream of water so that it doesn’t run off; allow the water to trickle all the way down through the deepest layers of soil.

The parent population of this plant thrives on fog drip in habitat. The rainy season is October to April, as in a Mediterranean climate.

A great trick for watering street trees is to drill a 1/8-inch hole on the bottom edge of a 5-gallon bucket, then set the bucket with the hole aligned next to the tree and fill the bucket with water. Fill once for a 1-5 gallon plant, fill twice for a 7-15 gallon plant, three times for 25g or larger plants.

Though these trees are drought tolerant, never let them go bone dry in a pot.
hardy
to		 25F
exposure Part Shade – Full Sun
indoor
outdoor		 Outdoor
drainage In Ground: Cactus Mix, In Pots: Cactus Mix, Tolerates Sandy Soil
fertilizing All Purpose, Low Needs
origin Hawai`i
california
native		 No
sunset
zones		 15–17, 20–H1

Sunset Zones Map

Outdoor Exposure Guide

OUTDOOR EXPOSURE GUIDE

Full Sun
Six or more hours of sun beams directly landing on the plant's leaves.

Part Shade
Three to five hours of sun beams directly landing on the plant's leaves.

Part Sun
One to two hours of sun beams directly landing on the plants leaves.

Full Shade
The plant is never fully lit by sun beams, but is in a bright spot or has dappled sunbeams playing over the leaves throughout the day.

Deep Shade
The plant never has dappled light on the leaves, and is in a place that feels dim, even on a nice sunny day.

SUNSET ZONES MAP

Growing Notes

Acacia are FAST growers. Unusual for the genus, this species is long-lived and has an upright habit when young. When it reaches the end of its life, you’ll have a nice source of hardwood.
Refrain from fertilizing unless growing in very poor soil like sand, in which case compost should suffice. Koa roots form symbiotic relationships with bacteria that help feed them.
Acacias can do well in pots, which effectively “dwarf” them. It’s worth trying with this species; let us know your results.
In partial shade, acacias look softer and the colors come out more. They also tend to get more upright as they reach for the sun.
This tree is forgiving of pruning. Prune off lower branches for a standard tree form, or tip prune or shear to create a dense shrub or screen. Best to prune during dry weather and at least a few hours before sunset.

Special Interest

Koa means bold, brave and fearless.
These plants originate from mother trees growing in a dry forest at high altitude, where they developed their tolerance for cold and drought on a tropical island.
Silky, golden hairs on new tip growth yields to silvery mature foliage.
Juvenile leaves are ferny. Adult foliage comprises sickle-shaped phyllodes.
Koa wood has been called the mahogany of Hawai`i. It is prized for canoe-building, paddles, furniture, and musical instruments.
Subtle, ball-shaped, cream-colored flower clusters appear through the year, with a peak in early spring. Fruits are bean pods.

More Info

Koa is the second-most common Hawaiian-endemic tree, after ʻōhiʻa (Metrosideros polymorpha).
May be useful as a street or avenue tree, but untested.