The Cooperative Extension Service of University of Hawai`i at Manoa, College of Tropical Agriculture and Human Resources (CTAHR) is an excellent source of factual, scientifically based information for commercial growers and homeowners alike. In Hilo, CTAHR is located at 875 Komohana Street, their phone number is (808)981-5199. They have both free and priced publications on subjects from Abiu to Zucchini and from Anthurium to Ulu. Check out their excellent website at www.ctahr.hawaii.edu
The Extension Office in Kona is in Kainaliu at 79-7381 Mamalahoa Highway; and in Kamuela at 67-5189 Kamamalu Street across from Church row. In addition, O`ahu, Maui and Kauai have Extension Offices.
Search the web for University Cooperative Extension Offices in your state. Often times a University Master Garden Program is located at the Extension Office. Master Gardeners have a wealth of knowledge for backyard gardeners. In Hilo, call them at (808) 981-5199, Monday, Tuesday and Friday from 9 AM till noon. You might also want to inquire about how you can become a Master Gardener.