Veg Connections: Perennial living mulch systems tested in organic sweet corn

The Northern Great Plains ecosystem presents many challenges for organic farmers. Faced with unpredictable springs, pest pressure, nutrient management hurdles and persistent weeds, organic farmers are constantly looking for innovative farm management strategies. Perennial living mulch systems offer one potential solution to help mitigate these challenges in the Northern Great Plains, which spans across Montana, the Dakotas, Wyoming, Nebraska in the U.S. and Alberta, Saskatchewan and Manitoba in Canada.

Living mulch systems are cover crops grown alongside the main cash crop during the growing season. Perennial living mulch systems can provide weed suppression and pest management and, when they include legume cover crops, may help offset nitrogen depletion.

However, previous research has shown that perennial living mulch systems can compete with the cash crop and decrease yields, particularly during the unpredictable growing seasons common to the Northern Great Plains.

South Dakota living mulch trials

Research using perennial living mulch was conducted in southeastern South Dakota in 2024 and 2025. The study evaluated three clover-based living mulch systems compared with bare ground control. The chosen clovers included red clover (Trifolium pratense), which grows by a taproot system; white clover (T. prestense); and white x kura clover (T. repens x ambiguum), which grow stolons and rhizomes, respectively.

The clover had been established two years prior to the sweet corn study and was seeded at rates from 7 to 12 pounds per acre. Each plot had been managed for two years using historical in-row systems that included tillage, tillage with pinned black woven landscape fabric, no-tillage and no-tillage with pinned black woven landscape fabric.

Sweet corn was planted into these plots, with conventional tillage and no-till practices maintained during both seasons; however, landscape fabric was not used during the corn growing seasons. The sweet corn plots were strip-tilled using a 12-inch blade pulled by a tractor, with two passes in 2024 and one pass in 2025 prior to planting. Strip-tillage was used to support germination from direct seeding, although germination was still delayed.

These results align with previous research showing that perennial clover and no-till soil management systems produce poor germination and high competition. Sweet corn was direct-seeded with a single-row planter behind a John Deere tractor at 8-inch spacing on May 14, 2024, and May 13, 2025.

Clover and weed biomass were collected multiple times throughout the season to compare living mulch and weed growth and performance. Sweet corn was harvested once half of the field silks had turned brown. Corn ears were graded using USDA husk-on and husk-off standards, including length, husk coverage, maturity, development and pest damage. Sweet corn grades were based on a scoring system in which a perfect ear (U.S. Fancy) scored 15 points, U.S. No. 1 scored 13 to 14 points, U.S. No. 2 scored 11 to 12 points and anything under 11 was considered unmarketable.

Yield and quality results

In 2024, total sweet corn yield was similar across all clover treatments, with only 15% to 20% of yield classified as unmarketable. Bare ground plots produced the lowest proportion of unmarketable yield and the highest percentage of U.S. No. 1 ears. Red clover produced the poorest-quality ears, with the highest percentage of unmarketable ears (20%) and a high percentage of U.S. No. 2 ears (40%).

Clover treatments delayed sweet corn production, allowing bare ground plots to be approximately one week ahead at all growth stages. Clover and weed biomass showed consistent growth throughout the season, with both decreasing once the sweet corn canopy closed over the clover. Historical use of tillage, tillage with fabric, no-till and no-till with fabric did not affect the corn harvest during the 2024 growing season.

Weather drives competition

During the 2025 growing season, a cool, wet spring increased competition between the sweet corn and clover living mulch, which provided the clover an early-season advantage. This caused the sweet corn in the clover plots to lag two weeks behind bare ground in production. Clover and weed biomass were much higher in the second year across all living mulch plots, and none of the clover systems achieved canopy closure.

Bare ground plots produced the highest number and quality of sweet corn ears during the 2025 growing season. Kura and red clover plots resulted in moderate production of U.S. No. 2 marketable ears. Sweet corn grown in white clover plots struggled throughout the season, showing both poor germination and poor ear quality. Bare ground and kura clover plots produced the highest percentages of U.S. Fancy and marketable sweet corn ears among all clover treatments.

Key takeaways

Clover, as a legume, remains an excellent candidate for integration with nitrogen-demanding cash crops. However, as observed during the 2025 season, clover can overpower the cash crop, especially during a cool, wet start to the season. Bare ground continued to produce the best sweet corn yields due to reduced competition and improved nutrient access.

Cash crops selected for living mulch systems must be chosen carefully, with consideration given to their response to clover competition and the broader balance of benefits and challenges. Living mulch systems should be evaluated within the context of highly variable weather patterns, pest pressure and nutrient availability.

Harms is a graduate research assistant at South Dakota State University and holds a bachelor of landscape architecture degree from the University of Nebraska-Lincoln. She has a passion for understanding and connecting people, local foods and the native ecosystem of the Northern Great Plains. Lang is an assistant professor and South Dakota State University Extension consumer horticulture specialist focused on local food and flower research and education.