Fertile soil and fewer pests are bright side of sunnhemp

Sunnhemp (Crotalaria juncea), a legume plant from South Asia identifiable by its bright yellow flowers, is becoming a common cover crop.

Tropic sunnhemp is an excellent source of organic nitrogen, which can reduce dependence on commercial fertilizers. In a home garden the sunnhemp plants can be plowed under as early as 30 to 50 days after planting.

Sunnhemp also helps with soil-borne pests and has shown promise in controlling nematodes. It was found to produce a compound known as monocrotaline that acts as a nematicide, which has the best effect on reniform and root-knot nematodes. Use of sunnhemp as part of a crop rotation can be an effective means of nematode management.

Above-ground sunnhemp acts as an insectory for beneficial insects such as pirate bugs, assassin bugs and parasitic wasps that in turn attack pests and their larvae.

Tropic Sun is a cultivar of sunnhemp that was developed in partnership with the Natural Resource Conservation Service and the University of Hawaii College of Tropical Agriculture and Human Resources. Seeds can be purchased from the Oahu Resource Conservation and Development Council (oahurcd.org) or the Molo­kai Seed Co. (www.molokai­seedcompany.com).

Growing requirements for Tropic Sun include a soil pH between 5 and 7. It can tolerate minimal soil fertility and water but performs well when fertilized and receives at least an inch of water per week. Year-round growth in Hawaii is possible at elevations of 0 to 1,000 feet, and at higher elevations with cooler temperatures. Plant in spring and summer months for best results. To establish sunnhemp, apply 40 to 60 pounds of seed per acre, doing broadcast application.

Do not allow sunnhemp plants to grow too long, as they will become hard to manage and incorporate into the soil. Fungal diseases might attack sunnhemp and reduce productivity in humid or rainy conditions.

For more information, visit goo.gl/4X44iW or call or visit your local UH-Master Gardener office.

Mahalo to Koon-Hui Wang, nematologist at UH, who has done such extensive research regarding the benefits of sunnhemp.

Sharon Motomura is a junior extension agent for the University of Hawaii College of Tropical Agriculture and Human Resources’ Cooperative Extension Service for Hawaii County.