Asparagus is best planted on well drained soils high in organic matter. The crop will tolerate brackish water. Asparagus roots are sometimes found at local garden shops. They could also be ordered through seed catalogs from the mainland. Check with the seed catalogs prior to ordering to see if they will ship to Hawaii.
Seeds are available at local garden shops as well as seed catalogs.
Plant anytime the roots are available. Buy roots 1 or 2 years old. If only seeds are available, plant in a seedling bed and transplant to the garden after a year's growth. Plants two years or more in age could be cut back twice a year after 5-6 months of growth and the spears harvested. Insufficient fertilizer, poor soil preparation, low organic matter, drought, acid soils, and allowing it to get too old before cutting can cause spears to be tough and pithy.