Evaluating planting methods and dates for interseeding annual ryegrass and crimson clover into fall cabbage in Northern New England, USA

Interseeding cover crops into standing vegetables may offer Northern New England growers a strategy to enhance soil health and reduce nutrient losses. However, the risk of failed cover crop seeding and cover crop competition with cash crops complicates management. We conducted two years of field trials (2022 and 2023) to evaluate the effects of interseeding annual ryegrass (Lolium multiflorum L.) and crimson clover (Trifolium incarnatum L.) into fall cabbage (Brassica oleracea L.) at 10, 21, and 30 days after transplanting (DAT), using three planting methods: broadcasting, broadcasting with incorporation, and drilling. We measured cover crop biomass, weed biomass, soil water, available nitrogen, and cabbage yield. Early interseeding (10 and 21 DAT) consistently produced the highest cover crop biomass, whereas later planting (30 DAT) reduced competition with cabbage. The higher cover crop biomass observed from early plantings correlated with lower yields and observable concerns of light and air movement reduction, underscoring a management trade-off between soil conservation benefits and crop productivity under contrasting seasonal moisture conditions. Cover crop planting method had no significant effect on cover crop biomass, although interactions with planting timing revealed benefits. Cover crops suppressed weed biomass relative to no cover crop control plots. In 2022, soil water variability showed a moderate correlation with cover crop biomass but was more strongly influenced by planting method and timing. Cabbage yield responses differed by year: in the dry 2022 season, later plantings (30 DAT) resulted in yields equal to the control, while in the wetter 2023 season, control plots outperformed all interseeded treatments. This highlights the trade-offs between maximizing cover crop benefits and minimizing competition with cabbage in a variable climate. Adaptive interseeding strategies, particularly delaying planting until later in the season, may help farmers balance soil conservation, weed suppression, and yield in short-season vegetable systems.