Cover Crop Trials

To increase adoption of cover crop use in Hawaii, field trials were established at 14 different sites. Sunn hemp, oats and buckwheat were planted to demonstrate their use in a variety of commercial crop settings.

Information on the following cover crops came from the College of Tropical Agriculture and Human Resources at the University of Hawaii at Manoa.

OLYMPUS DIGITAL CAMERASunnhemp (Crotalaria juncea) is a heat loving legume with yellow pea-type flowers. Originating in India and Pakistan, sunnhemp is an excellent green manure crop, with the ability to rapidly add nitrogen and organic matter to the soil. The ‘Tropic Sun’ variety produces a compound that is toxic to several nematodes. In Hawaii sunnhemp grows year-round at elevations up to 1000ft.  At higher elevations sunnhemp can be planted in the warmer spring and summer months.

  • excellent source of organic nitrogen, for increasing soil organic matter, for controlling root-knot nematodes, for loosening subsoil;
  • non-toxic to animals (unlike other Crotalaria species, which contain toxic alkaloids);
  • plow down before reaching full-bloom stage, or it becomes too fibrous;
  • use in annual production systems at lower elevations, including vegetables, herbs, cut flowers and ornamentals, and dryland taro.


CIG Molokai Rep 1 Oats 5_16_08

Common oats (Avena sativa) is a cool-season annual that has gained populatiry in Hawaii because of its ability to provide soil cover, suppress weeds and increase organic matter. Reaching a height of 2-5 feet, common oats has a fibrous root system that captures excess nitrogen and controls erosion. Common oats contains allelopathic compounds that suppress weeds, reducing the need for chemical weed control.


  • excellent for suppressing weeds due to rapid growth and establishment;
  • very good as a “catch crop” for taking up and storing excess N and providing erosion control;
  • good for increasing soil organic matter content to improve soil structure;
  • tolerates low fertility soils;
  • can be used as a nurse crop when planted at low densities;
  • use in annual production systems with vegetables, herbs, cut flowers, other ornamentals, and root crops such as dryland taro.

CIG Molokai Rep 1 Buckwheat 5_16_08

Buckwheat (Fagopyrum esculentum) is an annual grain that is used to suppress weeds, attract beneficial insects and build soil organic matter. Growing to heights of 2-5 feet, buckwheat has dense fibrous roots and white flowers. Its rapid growth habits make it an excellent green manure. In Hawaii buckwheat grows year-round at elevations ranging from sea level to 4000 feet.


  • excellent for suppressing weeds because of its quick growth and establishment;
  • excellent for attracting beneficial insects;
  • good for increasing soil organic matter and improving soil structure
  • tolerates a wide variety of soil types, including acidic and low fertility soils;
  • use in annual production systems with vegetables, herbs, cut flowers, other ornamentals, and dryland taro.