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Native Plants Journal 6.3 (2005) 228-232


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Propagation protocol for KOA Acacia koa Gray

Kim M Wilkinson

Environmental Management Specialist
PO Box 1331
Duvall, WA 98019
kim@kimwilkinson.com

Craig R Elevitch

Permanent Agriculture Resources
PO Box 428
Holualoa, HI 96725
cre@agroforestry.net
Keywords
Fabaceae, Hawai'i, scarification, Rhizobium inoculation
Nomenclature
USDA NRCS (2004)

Click for larger view		 Figure 1
Photo by Craig R. Elevitch
[End Page 228]
Koa (Acacia koa Gray [Fabaceae]) is native to all 6 major Hawaiian Islands: Hawai'i, Moloka'i, Maui, Lana'i, O'ahu, and Kaua'i. Its original range was from 90 to 2300 m (300 to 7500 ft). Today, the largest and most thriving koa trees are found between 900 and 1850 m (3000 to 6000 ft). Introduced pests and diseases limit koa's presence below 600 m (2000 ft).

Seed Collection, Processing, and Pretreatment

Flowering is seasonal in some areas, but in other areas it may occur year-round, with fruits ripening any time of year. Koa produces pods about 15 cm (6 in) long and 2 to 4 cm (1.0 to 1.5 in) wide. Each pod has 6 to 12 seeds. Pods are ready for harvest when brown, and when opened, seeds inside are deep brown and full (not green, flat, or small). Seeds may be collected from the tree by hand, with a pole pruner, or collected from the ground. Genetic quality is a crucial aspect of koa performance and yield, and source must be carefully considered and matched for the outplanting site before seeds are collected.

Pods are dried in the sun until they can be opened easily. Seeds are extracted by hand or by machine threshing. Once out of the pods, seeds may be dried more if necessary (ideal moisture content 6% to 8%). Dried seeds can then be stored in an airtight container away from direct sunlight. Properly dried seeds can be stored for 12 to 24 months at room temperature and for many years longer under cooler conditions. [End Page 229] Koa seed size is highly variable, there can be 1134 to 3402 seeds/kg (2500 and 7500 seeds/lb). Germination is usually 70% or higher but can be low depending on weather conditions during ripening.


Click for larger view		 Figure 2
A 2-wk-old seedling Photos by Craig R Elevitch

Click for larger view		 Figure 3
6-wk-old seedlings being spread to half density to improve growth.

Koa seeds require scarification. Me-chanical scarification (nicking with a nail clipper on the side opposite the point of attachment to the pod) is used for small lots. Hot water treatment also can be used: 90 °C (195 °F) in a volume ratio of at least 5 parts water to 1 part seed for 1 to 3 minutes. In all cases, scarified seeds are soaked overnight in cool water so that seeds fully imbibe before sowing. Following pretreatment, seeds germinate in 2 to 7 days.

Growing Seedlings

Koa seedlings can be grown in an uncovered growing area. If available, some cover (greenhouse or temporary cover) is ideal for the first 2 wk after germination to protect sprouts from hard rains or seed-eating birds. Rodents also eat koa seeds and should be controlled. Seeds are sown into Ray Leach cells that are 164 ml (7 in3) or greater in volume. We use a well-drained growing medium of 2:1:1:1 (v:v:v:v) peat moss, perlite, vermiculite, and compost amended with 4:4:2:1 (v:v:v:v) dolomite lime, gypsum, endo-mycorrhizal inoculant (Bio Organics™ Mycorrhizae Inoculants, La Pine, Oregon), and triple super phosphate at the rate of 2.5 l (88 oz) of amendments per 113 l (25 gal) of medium components.

Germinated seeds (sown on paper towels or in beds) are transplanted at a rate of 1 seed per cell into containers that have been prefilled with medium. We sow seeds as soon as the radicle emerges from the seed. Cover shallowly with medium mix, followed by a...

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