Understanding how to care for plants adapted to the Hawaiian volcano region's special conditions is vital to the long-term success of your garden. Species native to this area have evolved strategies to withstand cold temperatures, low light levels and high rainfall. Some endemic plants have even adapted to poor air quality caused by volcanic fumes. An understanding of the area's microclimates and forest composition can help guide the gardener in the care of these specially adapted plants.
The volcano area of Hawaii Island is located at elevations between 3,000 and 4,000 feet and receives an average annual rainfall of more than 100 inches. Temperatures can range from the mid 80s down to below freezing in winter. An environmental factor unique to this area is the occasional presence of sulfuric volcanic fumes, locally known as vog. In general, eastern parts of the region, near the summit, receive the most rainfall, and are best for plants native to the mixed wet forest. The slightly drier region, just west of the summit, is perfect for plants adapted to the light shade of the koa forests found there. Unlike exotic plants, native Volcano plants are not usually damaged by vog
Consider the specific conditions where the plant naturally grows when you select plants for your garden. Some species, like the graceful native lily, painiu (Astelia spp.), and many native ferns require dense shade. Others, like the attractive, small tree, mamaki (Pipturus albidus), and the colorful red stemmed Hawaiian pokeberry (Phytolacca sandwicensis) do well in partial sun at forest edges.
Most plants native to this region are easy to grow if they are planted in appropriate locations. The ohia lehua tree, which naturally springs up where other trees have fallen, leaving a light gap in the forest, must be planted in a sunny, but sheltered location. Hapuu pulu (Cibotium glaucum), a tall tree fern, grows in the shaded forest under story, and does best in protected shade. The koa tree (Acacia koa), which grows in the drier, western parts of the area, needs filtered sunlight, and must be inoculated when young with nitrogen fixing fungi found in the roots of mature koas.
It is generally unnecessary to amend the soil, unless the drainage is poor. In this case, consider adding black cinder or choose another location for the planting hole. Water your new plants well at planting, but afterward do not irrigate them except in extreme drought. Fertilize your plants sparingly in spring. Most volcano natives are adapted to poor leached soils and can actually be harmed by too much fertilizer. Healthy plants are seldom attacked by insect pests or pathogens.
On the island, protect your plants from introduced feral pigs, which can destroy patches of forest and entire gardens overnight. Pigs create wallows which fill with rainwater, creating a breeding ground for mosquitoes, which are carriers of avian malaria. Make a fence to keep pigs and other livestock out, so that safe habitat for native birds can be preserved. Invasive plants, such as glory bush, strawberry guava and faya tree choke out native vegetation and should be controlled.