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Acacia (koa)

Kim Wilkinson
Craig Elevitch
Permanent Agriculture Resources
P.O. Box 428
Holualoa, Hawaii 96725
808-324-4129 (fax)

Family Scientific Name: Fabaceae
Family Common Name: Legume
Scientific Name: Acacia koa Gray
Common Name: koa
General Distribution: Koa is native to the Hawaiian Islands. Found on all six major Hawaiian Islands: Hawaii, Molokai, Maui, Lanai, Oahu and Kauai. Original range: 300-7000 feet (90-2134 meters). Today, the largest and most thriving koa trees are found between 3000 and 6000 feet (915 and 1830 meters) elevation. Introduced pests and diseases limit their presence below 2000 feet.
Propagation Goal: plants
Propagation Method: seed
ProductType: Container (plug)
Time To Grow: 14 Weeks
Propagule Collection: Koa produces pods about 6 inches (15 cm) long and 1-1.5 inches (2-4 cm) wide. There are 6-12 seeds per pod. Pods are ready to pick when brown, and when opened the seeds inside are deep brown and full (not green, flat, or small). Seeds can also be collected from the ground. Koa can seed any time of year. 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.
Propagule Processing: 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 6-8%). Koa seed size is highly variable, and a pound of seed contains between 2500 and 7500 seeds. Dried seeds can then be stored in an airtight container away from direct sunlight. Properly dried seeds can store for 12-24 months at room temperature, many years longer in cooler conditions. Germination is usually 70% or higher, but can be low depending on weather conditions during ripening.
Pre-Planting Treatments: Scarification is required. Mechanical scarification (nicking with a nail clippers on the side opposite the point of attachment to the pod) is used for small lots. Hot water treatment (195 degrees F, 90 degrees C) in a volume ratio of at least 5 parts water to one part seed for 1-3 minutes. Sulfuric acid is another alternative, soaking time 10-60 minutes depending on seed size [this method is only recommended for trained laboratory technicians]. In all cases, scarified seeds are soaked overnight to allow water to penetrate into the seed. Seeds germinate in 2-7 days.
Growing Area Preparation/
Annual Practices for Perennial Crops:
Koa seedlings can be grown in an uncovered growing area. If available, some cover (greenhouse or temporary cover) is ideal for the first 2 weeks after germination to protect sprouts from hard rains or seed-eating birds. Rodents also eat koa seeds, and should be controlled. Containers used are super stubby cells (Ray Leach system) distributed through Stuewe & Sons, Inc. Most well-drained media work fine for this hardy pioneer species. One example media is 50% Sunshine peat moss, 25% perlite, 25% vermiculite, amended with a little compost, dolomite lime, gypsum, and triple super phosphate. Potting media should also be inoculated with VAM (mycorrhizal fungi), available from commercial suppliers and garden centers.
Establishment Phase: Scarified seeds will germinate in 2-7 days. Pregerminated seeds (sown on paper towels or in beds) are transplanted into tube containers that have been pre-filled with media at a rate of one seed per cell. Cover with potting mix shallowly (about 1/4 inch or 0.6 cm deep), followed by a thin mulch layer such as #2 poultry grit. Water with a fine-headed sprayer to keep moist. Full sun is best. Daily water is usually necessary, by hand or with an automated system.

After about six weeks, seedlings may be double-spaced in the Ray Leach trays to ensure each seedling receives full sunlight, and to facilitate good stem development. After one to two weeks of growth, seedlings should be inoculated with rhizobia bacteria selected for this species (available from commercial suppliers or from nodules collected from healthy forest trees). Select strains are best for optimum nodulation and nitrogen fixation.
Length of Establishment Phase: 2-3 weeks
Active Growth Phase: Seedlings are watered daily, usually in the morning. Especially hot, dry days may necessitate a second watering in the early afternoon. (Late afternoon and evening watering is not recommended, as it facilitates pest problems such as sooty molds.) The media should not be allowed to dry out. After about 6 weeks, seedlings may be double-spaced in the Ray Leach trays (from 98 trees per tray to 49 trees per tray) to ensure each seedling receives full sunlight, and to facilitate strong stem development. At the period, depending on seed lot, about 5-10% of the seedlings will be apparent poor performers, and these should be culled. Remaining seedlings are monitored for pests, but pests are generally not problematic in the nursery. If any weeds enter the soil-free media, they should be removed. No fertilizer application is necessary if seedlings were inoculated with rhizobia bacteria and mycorrhizal fungi. No pruning should be done.
Length of Active Growth Phase: 7-10 weeks
Hardening Phase: Since seedlings are kept outside, exposed to full sunlight, not fertilized, and watered as necessary during most of their life, a separate hardening off phase is usually not apparent. Growers should continue to ensure that seedlings continue to receive full sun, spacing seedlings out further if necessary. Seedlings should never be allowed to dry out, but watering frequency may be reduced to introduce seedlings to temporary, moderate water stress.
Length of Hardening Phase: 4-6 weeks
Harvesting, Storage and Shipping: When seedlings have reached target size, they may be delivered to the planting site. They are not extracted from their container or stored before shipping. Keeping them in their container is necessary to protect the roots and the viability of the rhizobia nodules. Containers may be stood up in cardboard boxes, or delivered in their trays. Seedlings must be protected from wind and excessive heat during transport, but refrigeration is not recommended. Empty containers and trays may be returned after the planting is complete.
Length of Storage: n/a
References: Dalla Rosa, Karl. 1994. Acacia koa-Hawaii's most valued native tree (NFTA 94-08). Nitrogen Fixing Tree Association, Morrilton, Arkansas.
Ferentinos, L. and D.O. Evans (Eds). 1997. Koa: A Decade of Growth. Proceedings of the 1996 Annual Symposium held by the Hawaii Forest Industry Association (HFIA), November 18-19, 1996. HFIA, Hilo.
Friday, J.B. 2000. Acacia koa. In: CAB International, Global Forestry Compendium, CAB International, Oxford, UK.
Little, Elbert L. and Roger G. Skolmen. 1989. Common Forest Trees of Hawai`i (Native and Introduced). United States Department of Agriculture Forest Service, Agriculture Handbook 679.
Loudat, T.A. and R. Kanter. 1996. The Economics of Commercial Koa Culture in Hawaii. In: Koa: A Decade of Growth. Hawaii Forest Industry Association (HFIA), Hilo.
Skolmen, Roger G. 1986. "Where Can Koa Be Grown." In: Proceedings, Resource Conservation and Development (RC&D) Koa Conference. RC&D Forestry Committee with DLNR/DOFAW and USDA FS, Hilo.
Wagner W.L., D.R. Herbst, and S.H.Sohmer. 1999. Manual of the Flowering Plants of Hawaii, Revised edition. University of Hawaii Press, Honolulu.
Whitesell, Craig D. 1990. Acacia koa A. Gray. In: Burns, R.M., and B. Honkala. Silvics of North America Vol. 2: Hardwoods. USDA Forest Service Handbook No. 654, 17-28.
Wagner WL, Herbst DR, Sohmer SH. 1990. Manual of the flowering plants of Hawaii. University of Hawaii Press and Bishop Museum Press. Honolulu, HI. 2 volumes. 1854 pp.
Wilkinson, Kim M. and Craig R. Elevitch. 2003. Growing Koa: A Hawaiian Legacy Tree. Permanent Agriculture Resources, Holualoa, HI.


Elevitch, Craig Randall; Wilkinson, Kim Marie. 2004. Propagation protocol for production of Container (plug) Acacia koa Gray plants Permanent Agriculture Resources Holualoa, Hawaii. In: Native Plant Network. URL: http://NativePlantNetwork.org (accessed 2021/07/27). US Department of Agriculture, Forest Service, National Center for Reforestation, Nurseries, and Genetic Resources.

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