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Acacia (koaia)

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 koaia Hillebr.
Common Name: koai`a, koai`e
Ecotype: Native to lowland dry forests of the Hawaiian Islands
General Distribution: Koai`a is endemic to the Hawaiian Islands of Molokai, Kauai, Lanai, Maui, and Hawaii. Now thought to be extinct on Maui and Molokai. An endangered species.
Propagation Goal: plants
Propagation Method: seed
ProductType: Container (plug)
Time To Grow: 0
Target Specifications: Seedlings have reached target when approximately 15-20 cm in height, stem diameter 6-8 mm, with well-formed root systems that are not root-bound but that fill out the container.
Propagule Collection: Koai'a produces pods about 5 inches long. 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 be collected from the tree or from the ground. Koai`a can seed intermittently any time of year, although late summer tends to be the most abundant.
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%). 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 around 50%. Insect damage to the seeds from the koa seedworm and the haole koa seed weevil may be evident. Seeds may be frozen for about 24 hours to ensure that any insects in the processed seeds expire before seeds are put into storage.
Pre-Planting Treatments: Scarification is required. Because the tree is endangered and seeds are precious, mechanical scarification is recommended for highest viablility. This is done by nicking with a nail clippers on the side opposite the point of attachment to the pod. 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 minutes may be used on larger seed lots, but may also damage some seeds. In all cases, scarified seeds are soaked 12-24 hours to allow seeds to imbibe water. They may then be spread out on paper towels and covered with a single layer of paper towel until germination. Seeds germinate in 2-7 days.
Growing Area Preparation/
Annual Practices for Perennial Crops:
Seedlings are grown in full sun in an uncovered growing area. Containers used are Ray Leach Super "Stubby" Cells 14 cm deep and 3.8 cm diameter (available from Stuewe & Sons). A well-drained potting media such as 50% Sunshine peat moss, 25% perlite, 25% vermiculite, amended with a little compost, dolomite lime, gypsum, micronutrients, P and K is used. Potting media should also be inoculated with VAM (mycorrhizal fungi), available from commercial suppliers and garden centers. At planting time or within 2 weeks of planting, rhizobia inoculant should also be applied (see below).
Establishment Phase: Pregerminated seeds are placed in containers filled with premoistened potting media and covered with about 5mm of potting media and a thin layer of mulch (such as #2 poultry grit). Water with a fine-headed sprayer to keep moist. For the first 2-4 weeks, some cover (greenhouse or temporary cover) is best to protect sprouts from hard rains. The area should be protected from koai`a seed predators including rats, mice, and some birds including cardinals. Daily water is usually necessary, by hand or with an automated system. At seedling time or within 2 weeks of germination, seedlings may be inoculated with rhizobia bacteria (a nitrogen-fixing bacteria). This may be available from commercial suppliers or homemade from nodules collected from healthy koai`a trees. The partnership with rhizobia bacteria is necessary for good nodulation and growth.
Length of Establishment Phase: 2 weeks
Active Growth Phase: Seedlings can be moved to full sun in an open area 2-4 weeks after sowing. After about ten weeks, seedlings are double-spaced to allow maximum penetration of sunlight and air circulation. If seedlings were inoculated with rhizobia bacteria, no additional fertilization will be necessary. If inoculation was unsuccessful, amending with additional fertilizer such as a light top dressing of Gro-More 8-8-8 will aid in growth and development. If any weeds enter the soil-free media, they should be removed. Insect problems are usually minimal in the nursery, although older trees are susceptible to attack from twig borers. Coffee twig borers and black twig borers may be deterred (although not altogether eliminated) by twice-weekly foliar spray of neem oil (apply in aqueous solution according to product instructions).
Length of Active Growth Phase: 4 months
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 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 seedlings in their container is necessary to protect the roots. Containers may be stood up in cardboard boxes, or delivered in 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.
Other Comments: Acacia koaia is now recognized as a distinct species from its close relative Acacia koa, and is classified as endangered. It is smaller than koa and more tolerant of drought and low elevations, making it more suitable for landscaping. Its wood is harder and heavier than koa, and is valued even more highly than koa by many woodworkers.
References: Bornhorst, Heidi L. 1996. Growing native Hawaiian plants: a How-to Guide for the Gardener. The Bess Press, Honolulu.
National Tropical Botanical Garden (NTBG). 1990. Plant of the Month: Koaia. Hawaii Plant Conservation Center, NTBG, Lawai, HI.
Nitrogen Fixing Tree Association. 1990. Native Nitrogen Fixing Trees of Hawai`i. NFTA, Waimanalo, HI.
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.


Elevitch, Craig R.; Wilkinson, Kim M.. 2004. Propagation protocol for production of Container (plug) Acacia koaia Hillebr. plants Permanent Agriculture Resources Holualoa, Hawaii. In: Native Plant Network. URL: http://NativePlantNetwork.org (accessed 2021/09/19). US Department of Agriculture, Forest Service, National Center for Reforestation, Nurseries, and Genetic Resources.

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