Hawaii Arbor Day is celebrated on the first Friday of November. Amy B.H. Greenwell Ethnobotanical Garden has taken part in Arbor Day tree giveaways for the past 15 years. This year’s celebration will last three days, Nov. 7 to 9. One tree per person will be available, from 9 a.m. to 1 p.m. at the Greenwell Garden visitor center in Captain Cook. All of the trees and shrubs are either native or Polynesian introduced.
The trees at the giveaway include favorite natives such as koa and kou. These trees are suited to very different landscape situations. Kou is a medium-sized tree used frequently for shade in parking lots. It does best at low elevations to about 2,000 feet. Kou has pretty orange flowers, which are great for making lei. The wood makes excellent bowls and poi boards. Koa is a large tree which does best at higher elevations starting around 2,500 feet. The wood is prized for canoes and furniture.
Polynesian-introduced plants provide a link to Hawaiian culture. You can enjoy the shade of a kukui, as people have for more than 1,000 years in Hawaii. This fast-growing tree is a beautiful addition to a garden and it is good at helping convert lava to rich soil. The only fruit tree that will be available at the giveaway is mountain apple. Ohia ai arrived in Hawaii with the Polynesian settlers. Its fruit resembles apples in flavor, though it is shaped more like a pear.
Several native shrubs with beautiful flowers will also be available. Mao hau hele is an acid yellow hibiscus that has been designated the state flower of Hawaii. It is a fast-growing, sprawling shrub that blooms year-round. Kokio keokeo has large white flowers with pink staminal columns. What really sets it apart is a wonderful citrusy fragrance. It is the only fragrant hibiscus in the world and is native to Kauai. Alahee is a shrub in the coffee family. When it blooms you can smell its cinnamon fragrance from the far side of the garden. Alahee is a dry-adapted survivor, and there are many in the disturbed, weedy landscape around Kailua-Kona.
Other plants that will be available are milo, kamani, manele and hala. Milo is great for hedges and screens. Kamani is a spreading shade tree that does very well near the coast. Manele occurs naturally at high elevation, but a gardener from near sea level in Kohala has reported that manele is one of the best performing trees on his property. Hala is a striking accent tree with dramatic tufts of long, slender leaves and prop roots that look like legs that might carry it across the landscape.
When you come to Greenwell Garden for your tree, you will be able to watch woodworkers making poi boards from slabs of wood. The woodworkers will use modern tools to fashion these essential accessories of traditional life in Hawaii. Some may make poi stones as well. These are the basalt pestles used to make poi from taro corms.
A guided Hawaiian plant walk begins at 1 p.m. Participants will see mature examples of the plant they have chosen from the giveaway and learn about its use and care requirements. An award from the County of Hawaii Department of Research and Development and the Hawaii Tourism Authority funds the guided walks offered at 1 p.m. Tuesday through Sunday. If you require an auxiliary aid or service for effective communication or a modification of policies and procedures to participate in the walk, contact Peter Van Dyke at 323-3318 at least two weeks before your planned visit.
Peter Van Dyke is the manager of Amy B.H. Greenwell Ethnobotanical Garden in Captain Cook.
Tropical gardening helpline
Shelby asks: We have a sheared false olive hedge around our property in Waimea. It is about 6 feet tall and 5 feet thick. Lately it has become infested with white fly so that a cloud surrounds you as you trim the hedge. It is difficult to spray soap or oil into the hedge. How do I control the infestation?
Answer: More than 1,000 white fly species exist in the world and sometimes we may think we have them all in our garden. Infestations in Hawaii can be severe. Weather fluctuations and nutrient deficiencies affect the health of the plant and as they deteriorate they become susceptible to insect invasions. Here are some ideas you might try on the hedge that you describe.
You could start by pruning off the most severely infested parts of the hedge. Limit your pruning to about one-third of the hedge. Pruning will stimulate new growth that will attract white flies, so you’ll have to keep on your other control measures, but the pruning will initially reduce the area you have to deal with. Be sure to place the infested material in sealed plastic bags and dispose of properly.
University of California studies have shown that spraying the underside of infested leaves with a strong stream of water works as well or better than chemical treatments. Try that as soon as you do the pruning and repeat as often as possible. This will wash off many of the white flies, as well as the honeydew they produce. Though some will return, if you do this often enough most of the white flies will likely give up.
You can also try using insecticidal yellow sticky cards. They can help reduce light or new infestations. Place the cards adjacent or just above the infested areas. The insects are attracted to yellow and will stick to the card when they land. Once the cards get full they lose their effectiveness and should be replaced.
In small areas of infestation you may be able to repel the white flies by attaching aluminum foil to some of the branches.
If ants are present, you should try to eliminate them. They are often larger than white fly predators and will discourage them. Ants are also motivated to protect the white flies as they “farm” their sweet excretions called honeydew.
If all else fails go for a spray of a safer soap and neem oil combination. This can help control the white fly and ant populations but will also affect any predators and parasites that might be around.
Email plant questions to konamg@ctahr.hawaii.edu for answers by certified master gardeners. Some questions will be chosen for inclusion in this column.
This column is produced by Diana Duff, a plant adviser, educator and consultant living on an organic farm in Captain Cook.