Information on Hardiness Zones
I live on Maui and many people don't realize that Hawaii isn't purely a tropical climate. I have serious issues with the USDA's hardiness zone map. Here at a mere 1,3000 feet of elevation, I have no trouble getting zone 8 plants to grow. Meanwhile, few zone 11 plants will survive the altitude and occasional frosts. With such a wide range of conditions, is there a better way to get a more accurate zone map for my area?
The USDA hardiness map is just one measure of a plant's suitability to a growing area. Every new revision to the hardiness map tries to account for microclimates resulting from large bodies of water, elevation and urban heat islands. Unfortunately it is impossible to adequately evaluate all growing locations.
A look at the Sunset Western Garden Book shows how elevation and the ocean create a diverse growing region in the western part of the United States. I have not been able to find a comparable book for your location.
No matter where you live, however, the local University Extension Service and Botanical gardens can provide good information specifically for your growing conditions. You might want to contact or visit the Kula Botanical Garden located on Kekaulike Highway near Kula Highway. It is located at 3,300 feet and has 6 acres of gardens with both tropical and semi-tropical plants. The Kahului Cooperative Extension Office at the Maui Community College in Kahului Hawaii may also be able to provide some helpful tips for gardening in your location.