The very thought of Hawaii can evoke images of swaying palm trees, warm ocean water and sandy beaches. Some parts of the Islands, however, have no soil at all, presenting a challenge to farmers and backyard gardeners. Another problem is represented by the invasive species that have taken over many areas, especially at the lower elevations. Where native plants once dominated the landscape, many have already become extinct and many more are endangered.
On the Big Island of Hawaii, lava flows from Kilauea volcano continue to add acreage to this largest of the Hawaiian Islands. In many places along the southern half of this island, lava that covered the land as recently as 500 years ago has not yet had time to break down into rich, nutritious soil, so many gardeners must purchase topsoil and compost to build up raised beds if they want to grow fruit trees, vegetables and ornamentals. Purchased soil comes from old sugar cane acreage and other agricultural lands where soil does exist.
Tropical fruit and nut trees, vegetables, Hawaiian native plants and ornamentals will grow well in raised beds built on top of rock. You can make the planting medium in your beds very rich and well draining if you use a combination of topsoil, compost, lava cinder and other organic materials.
Sandy, Salty Soil
Areas near the ocean on the older, more northerly islands contain very sandy, salty soil. Gardeners must enrich this type of soil with compost and other organic materials to turn it into a rich humus or loam that will hold moisture better than sand and provide nutrients to the plants that grow there. Some soils near the ocean are so salty that salt poisoning occurs, making it almost impossible to grow many plants, such as orchids.
Coconut palms and other so-called beach plants, such as the native naupaka and purslane, grow well in sandy, salty soil. Unfortunately, so do some of the plants classified as invasive species. These include ironwood trees, strawberry and yellow guava, autograph trees, melastoma shrubs and others.
Some areas in the windward hills do contain good soil for growing crops such as papayas, pineapples and sugar cane. The volcanic ash and cinder that these soils contain often makes the soil reddish in appearance. A University of Hawaii associated website reports that even the best of Hawaiian soils has poor conductivity and “terrible retention of nutrients.” Copious amounts of rain quickly leach nutrients from the soil, forcing many farmers and home gardeners to resort to using large quantities of fertilizer to maintain the conditions that their crops require.
Areas having developed soils have long been used for commercial agriculture in the Hawaiian Islands. Common crops have included sugar cane, pineapples, papayas, mangos and other fruit trees, bananas, bamboo, turmeric, taro, sweet potatoes and more. Because of competition with developing tropical countries such as the Philippines, crops like sugar cane and pineapples are not being farmed on a large scale basis any longer in Hawaii.