MSU Extension Grapes

Bridging the cover crop knowledge gap in Michigan viticulture

In the evolving landscape of Michigan viticulture, where climate variability, increasing input costs and long-term soil health challenges are pressing concerns, the promise of cover crops has largely gone unrealized. Unlike in California and Oregon, without mentioning Europe, where vineyards actively use cover crops as tools for ecosystem services, Michigan’s grape industry remains cautious and under-informed.

One striking indication of this gap is the historical absence of funded research on vineyard cover cropping in the state. Even when growers express interest, funding agencies often decline to support new trials, citing a lack of visible short-term benefits. This circular logic—no trials because there’s no data, no data because there are no trials—has delayed innovation in a region that otherwise could lead the Midwest in sustainable grape and wine production.

This article aims to break that cycle and provide a grounded roadmap forward. Drawing from more than 30 years of cool-climate vineyard research, from Canada to northern Europe, we highlight how cover crops can strengthen Michigan’s soils, fruit quality and vineyard resilience. Cover crops aren’t just a soil conservation tool, they are a smart, science-backed strategy that lowers costs, supports vine balance and helps vineyards adapt to climate pressure.

Understanding soil function in cool-climate vineyards

Soil as a living system

Healthy vineyard soils breathe. They host dynamic microbial populations, maintain structural porosity and supply a steady stream of nutrients as organic material breaks down. These are not static properties, they are actively influenced by management. Unfortunately, in Michigan, vineyard soils are often compacted by numerous spring tractor passes due to repeated pesticide application, low in organic matter (sandy soils) and poorly aggregated due to historical tillage and herbicide use. Research across cool-climate regions has confirmed that cover crops enhance soil organic carbon levels, microbial biomass and water infiltration. These improvements are not cosmetic, they directly translate into deeper rooting, improved nutrient uptake and better drought resilience.

Drawing on our field observations, soils with established multi-species covers, especially mixes of grass, legume and brassica, sustain improved aggregate stability and higher microbial respiration, even post-termination. This creates a more buffered system capable of responding to rainfall and improving early root zone aeration. In the face of increasingly unpredictable environmental influences, such as variable spring warming timing, early and late frost events, or prolonged dry spells, these cover systems act as stabilizers. They offer critical support to young and mature vines alike, helping maintain root zone health and reducing susceptibility to abiotic stressors like temperature and moisture extremes.

Soil texture, parent material and structure

Not all Michigan vineyard soils are the same. Some regions are dominated by heavy clay loams with low infiltration rates and high compaction risk, while others, especially along the western slope, feature deep sandy profiles with gravel and glacial stone. Understanding your site’s parent material helps determine what kind of cover cropping will be most effective.

In several Michigan sites, we deal with coarse soils where limestone is present, but not always shallow enough to influence rooting. Instead, growers often face stratified sands or stony subsoils with poor water-holding capacity. In these settings, even modest increases in soil organic matter can lead to meaningful gains in structure and biological activity.

Building soil organic matter (SOM)

Cover crops contribute to SOM through root exudates and above-ground biomass that is eventually incorporated or decomposed. But their effect is more than additive. They help build the architecture that protects organic matter from oxidation and leaching. Soil organic matter is more than just stored carbon; it’s the backbone of water retention and nutrient availability. As SOM increases, so does a soil’s ability to hold water and support microbial life. That’s why structured soils with 3–5% SOM show better infiltration, higher field capacity and stronger microbial nutrient cycling. For vineyards in variable rainfall zones, this buffering capacity is essential.

Root systems and microbial partnerships

Cover crops do more than grow roots, they grow microbial partnerships. Different species support unique consortia of bacteria, fungi and invertebrates that persist well beyond termination. The right mix can increase nitrogen cycling, improve mycorrhizal associations, and buffer against soil pathogens.

The real magic happens in blends. Multispecies cover crop mixes unlock a greater microbial repertoire. We have observed vineyards with robust cover blends exhibit more resilient vine growth under pressure. That’s not just correlation; it’s the system’s biology working in your favor. When we feed the soil with diverse root exudates, we activate more of the microbial spectrum, which helps vines access nutrients more efficiently and builds legacy benefits into future seasons.

Selecting cover crops for vineyard systems

Choosing a cover crop is not just about finding something green to grow. It’s about selecting species, or blends, that will contribute to your site’s goals: soil improvement, nutrient cycling, pest suppression or biodiversity. Every vineyard is unique, and the “right” cover will depend on vine age, soil texture, climate and management constraints.

Species selection

Choosing a cover crop species should not be treated as an afterthought. Each species offers different traits: legumes fix nitrogen, grasses scavenge nutrients and build biomass, brassicas penetrate compacted soil. Each of these functional groups plays a role in the vineyard ecosystem.

When selecting species, also consider that shallow-rooted grasses may not be as helpful in drought conditions, whereas deeper tap-rooted species like tillage radish or safflower can increase vertical porosity. Additionally, carefully timed legumes can fix nitrogen without encouraging excess vigor if terminated at the right time. A multi-species blend is preferred to ensure both ecological coverage and functional layering.

Seeding rate and termination

Seeding rates depend on your species and blend goals: for example, annual ryegrass might range from 30–60 pounds per acre (34–67 kilograms per hectare), but if blending multiple species, individual components should be reduced proportionally to maintain balance and reduce overcrowding. Terminating cover crops three to five weeks before budbreak to minimize frost entrapment and reduce early water/nutrient competition is an important consideration in Michigan. Termination options are multiple, so we don’t assume chemical burndown is the only path.

Use mowing and roller-crimping (try to avoid chemical burndown) as appropriate for species and system goals. Mowing, crimping and rotational tillage can be used selectively to meet organic or reduced-input goals. Mechanical options are particularly effective with cereals or vetch blends at appropriate growth stages.

Weed suppression and herbicide reduction

Cover crops provide physical, chemical and competitive barriers to weed growth. Rye, mustard and buckwheat are especially effective:

• Dense canopy shades out light-loving annual weeds.
• Rye and mustard produce allelopathic compounds that inhibit weed germination.
• Mulched residue creates a suppressive mulch for four to six weeks post-termination.

In several Michigan vineyards, we have seen that timing and species selection are especially critical for maximizing weed suppression without disrupting vine balance. Fast-establishing species like buckwheat or mustard can create rapid canopy closure, but these should be terminated before they become woody or compete too aggressively.

Additionally, mechanical under-vine management combined with inter-row cover cropping can reduce the need for synthetic herbicide passes. This integrated approach supports both weed control and long-term soil structure improvements.

Influence on grape quality

Grape composition is influenced by water availability, vine vigor and canopy structure, all of which are modulated by cover crops. Moderate competition early in the season promotes shorter internodes, better cluster exposure, and enhanced fruit quality.

Benefits include:

• Increased skin-to-pulp ratio.
• Improved color and anthocyanin content.
• Fast acid degradation in hot years.

While our existing cover crop experiences and anecdotes are encouraging, we are excited to explore further benefits in cool-climate varieties such as Chardonnay, Sauvignon Blanc and Riesling in collaboration with several growers of the northwest and southwest part of the state. These cultivars, often grown for their crisp acid profiles and balanced phenolics, may benefit from modest cover-induced stress early in the season to refine fruit quality and harvest chemistry.

Microbial diversity and soil biology

Living roots don’t just grow plants, they sustain microbial life. During dormancy, soils without active vegetation can lose key microbial functions, entering a biological “shutdown” that reduces nutrient cycling, root-microbe communication, and natural disease resistance. Cover crops extend the period of microbial activity through fall and early spring, keeping the biological engine running even when vines are at rest.

Cover crops help preserve and amplify:

• Earthworms – increase aggregation, water movement and surface residue breakdown.
• Mycorrhizal fungi – form critical symbiotic networks that enhance phosphorus and micronutrient uptake.
• Disease-suppressive bacteria – reduce pressure from soilborne pathogens by occupying root space and secreting protective compounds.

Microbial diversity is a vineyard’s invisible insurance policy. Once established, diverse microbial networks persist long after mowing or winterkill, especially when cover roots overlap vine roots. We have observed that these biological “legacies” not only improve nutrient efficiency but also enhance early season vigor and buffer against transient stressors. In low-organic matter soils, this microbial continuity is often the difference between sluggish spring growth and a strong, uniform start.

Resilience to weather extremes and carbon storage

Cover crops increase soil carbon, reduce surface temperatures, and buffer against drought. Zhang et al. (2022) found perennial cover crops in vineyards sequestered 0.4 Mg carbon per hectare per year (0.36 tons per acre per year), far exceeding what bare soil can store. This helps stabilize soil structure under extreme rainfall and protects against compaction from mechanical operations. In Michigan, we are finding cover crops increasingly more useful to deploy as risk-management strategies against a range of weather extremes, such as drought, heat, erratic rainfall and unpredictable spring conditions. Cover crops buffer against these pressures by insulating the soil, improving infiltration and maintaining microbial activity despite stress events.

Designing and managing cover crop programs in Michigan vineyards

Cover crop success hinges on species selection, timing, termination strategy, and how they fit into the broader vineyard management calendar.

Timing windows in cool-climate systems

Seeding windows are narrow in Michigan due to frost risk and limited heat units. Aim for early to mid-August for fall-seeded covers or late April through May for spring seeding. Soil moisture considerations are important when planning your planting cycles. There are also other competing priorities during these windows such as pre-bud break pruning, or in the fall window, harvest is looming.

Intentional planning around labor availability and equipment logistics helps ensure your cover crop gets in on time. Species like buckwheat and phacelia also offer pollinator habitat but must be seeded early enough to flower before frost. In our Michigan vineyards, we can experience a killing frost as early as late September. We really need six to eight weeks from planting to engage the benefits of the cover crop, so we should be cognizant of impending frost that could thwart our efforts by killing our late summer covers before they’re mature enough to contribute value.

Functional group selection by objective

Different species offer different outcomes: legumes fix nitrogen, grasses offer biomass and scavenging, brassicas break compaction. Use species blends that target more than one goal. The following table outlines common cover crop types and their benefits. We have added ideal planting windows and matched soil conditions to make this regionally useful. This helps growers decide which blends make sense based on their field goals and constraints.

Managing regrowth, reseeding and nutrient cycling

Effective post-termination management is essential for sustaining the benefits of cover cropping. It's important to recognize that some species, such as annual ryegrass or vetch, may regrow if not fully terminated. This should be factored into your workflow. In contrast, certain species like buckwheat are often intentionally allowed to self-reseed, especially when supporting pollinator habitat is a goal. Letting buckwheat set seed before mowing enables natural reseeding, reducing the need for additional passes or seed input.

To evaluate nutrient cycling, consider conducting a total nutrient digest test on the cover crop biomass at termination. This provides insights into what nutrients are returning to the soil. Pay particular attention to the carbon-to-nitrogen (C:N) ratio: low C:N ratios lead to faster nutrient release, while high ratios (above 20:1) can temporarily immobilize nitrogen during decomposition.

For nitrogen management, petiole nitrate sampling is especially helpful in moderate- to high-vigor cultivars like Riesling, Sauvignon Blanc or Chambourcin. However, in low-vigor blocks, whole-tissue sampling or visual monitoring may be more appropriate to avoid overestimating nitrogen needs.

Ultimately, the termination process isn’t just about ending cover crop growth, it’s about actively managing the biological and nutrient dynamics that follow. When uncertain, scout the field and take samples. These actions will help fine-tune both nutrient timing and future cover crop species selection.

Soil is a vineyard’s most underused asset

The next chapter of Michigan viticulture will begin in the soil. And not just any soil, but living systems that are biologically active, structurally sound and resilient across seasons. When thoughtfully managed, cover crops offer growers a powerful way to transform depleted or at-risk soils into healthier, more functional ecosystems, without relying entirely on external inputs. These strategies aren’t limited to organic farms or estate vineyards. Any grower committed to vine health, fruit quality and long-term sustainability can benefit from harnessing the biology beneath their feet.

While Michigan has been slow to invest in vineyard cover crop research, we need to act. Cool-climate studies from around the world consistently show that even modest cover crop programs can enhance soil health, reduce dependency on synthetic inputs, and help vines better withstand climate variability. To fully unlock this potential, Michigan needs a coordinated, long-term, multidisciplinary research effort, one that evaluates not only vine performance and soil health, but also pest ecology, grape composition, climate interactions, and grower economics. Without such investment, the state risks falling behind regions that have already embraced cover crops as a foundation of innovative viticulture.