Why Should You Plant Cover Crops in Your Garden?

Cover crops are an excellent way for home gardeners to improve their soil health, reduce weed pressure, control pests and diseases, prevent erosion, and retain soil moisture. 

Before selecting types and varieties, ask yourself: 

• What are my goals? 
• What is my timeline? 
• Can I terminate these cover crops properly using the garden methods and tools I have? 
• What cover crops are compatible with my climate? 

You’ll notice an overlap in the benefits of some of the cover crops discussed here, and that’s because most cover crops have multiple benefits. The keys are knowing your garden’s limitations, the advantages of various cover crops, and the best way to terminate them.

To learn more about termination methods you can check out Cover Crops for Successful Land Management from our market gardening blog. 

1. Improved Soil Health

Enhanced Soil Structure

Soil structure and texture prevent compaction and help hold in nutrients. Soil structure refers to how soil particles are positioned and interact with one another and is negatively affected by excessive tillage, too much sodium, cultivation, and compaction. Soil texture refers to the type of particles your soil is comprised of, like clay, sand, or silt as well as organic matter content. Gardeners should strive for loamy, rich soil containing about 3 to 5% organic matter. Cover crops increase organic matter in the soil as the roots and foliage from terminated crops break down. 

Soil that is covered with crops is safe from compaction caused by rain, hail, wildlife, and machinery. Rotating cover crops improves the soil’s holding capacity of moisture and nutrients, resisting erosion and keeping carbon out of the atmosphere.

Deep-rooted daikon radishes and sunflowers help break up compaction, whereas legumes and grasses cut several times a year lead to increased soil carbon, organic matter and improved soil health. 

Related: How to Determine the Texture of Soil 

Increased Organic Matter

As with all plants, cover crops produce more plant matter as they grow. When cover crops die back, are terminated, smothered, and tarped, debris begins to break down, adding nutritious organic matter to your soil, both on the surface in biomass and underneath the soil as their roots decompose. 

Earthworms and other invertebrates tunnel through to consume the top layer of newly decomposing matter. They leave behind castings and aeration tunnels that further improve the soil structure. These castings feed and increase beneficial soil microbes. Organic matter increases water retention, smothers weed germination, allows the soil to retain nutrients, makes nutrients available for crops, and keeps the soil cool.

Cover crops like buckwheat, crimson clover, sorghum, and partridge peas create a lot of plant matter. As they break down after being terminated, they provide food for microbes and help you reach that 3 to 5% organic matter in your soil. 

Nutrient Management

Many cover crops serve your garden as nutrient scavengers, which means they send roots deep into the soil in search of nutrients like magnesium, potassium, and calcium, all vital for maintaining healthy plants. 

Legumes like clover, peas, fava beans, and hairy vetch hold nitrogen as nodules in their root systems, which are available during the next crop cycle. As the roots decompose, nitrogen is slowly released back into the soil. 

Pro tip: Leafy greens like spinach, lettuce, and cabbage will appreciate the nitrogen boost and assist in leaf production when planted after legumes.  

While cover cropping is a “long game,” planting legumes and grasses is the first step in the journey. Legumes perform biological nitrogen fixation (BNF), which is essential since nitrogen is a crucial building block for a healthy garden and producing high-protein crops. 

Legumes are gaining popularity for their ability to perform BNF and improve soil structure. In simple terms, legumes form a symbiotic relationship with rhizobia in the soil. Soon after legumes germinate, rhizobia invade the roots, plump them up, and form nodules, which will later store nitrogen by fixation. Up to 50 to 80% of their nitrogen needs can be fulfilled through BNF, and they serve as a homegrown slow-release nitrogen fertilizer if the crop is terminated before seed pod production. 

2. Weed Suppression

Natural Weed Barrier

We can all use a little help with weed control, right? Covering the soil with cover crops when not in use effectively suppresses annual weed seeds from germinating. Heavy weed pressure creates competition for garden crops that will slow their growth and decrease yields. 

Consider buckwheat as a spring or summer cover crop. It germinates and matures quickly, attracts beneficial insects and pollinators, and produces loads of biomass when terminated. Its large flowers effectively suppress weeds from germinating, and it continues to offer this service when it is flattened across the soil surface and breaking down. 

Growers in colder regions should consider winter rye because it germinates in cooler temperatures, has a high biomass when knocked down, and blocks spring-emerging weeds when overwintered. Winter rye seeds can be undersown in late summer or fall with fall crops to allow them to establish before the first frost and winter. According to this study by C. Sangeetha and P. Baskar in Academic Journals, rye releases allelochemicals that suppress weeds, acting as a natural herbicide, when used as a cover crop and green manure. Cereal rye affects pigweed, lambsquarter, purslane, and crabgrass. A similar effect occurs when sorghum suppresses Bermuda grasses and nutsedges. 

Note that ryes require proper timing for sowing and termination and controlled residue management for best results. Otherwise, they may re-establish.

Related: Cover Crops for Successful Land Management | Fall Cover Cropping

Using Silage Tarps

Silage tarps help create a stale seedbed in new growing areas or those with a large weed seed bank. A stale seedbed is an area of a garden where the weed seeds have been germinated and killed, which makes germinating crop seeds easier and gives transplants the best chance at success. 

You can accomplish a weedless area by pulling a tarp over a garden plot or making strips of a tarp that fit over bed rows. Annual weeds have a specific life cycle, so if a tarp covers the soil for a few weeks or months, those weeds will either germinate and die or be unable to germinate from lack of light. If you cover an area for 12 months, in theory, all annual seeds will be gone, and you’ll have a year of “weed-free” growing. Refer to our article Using Silage Tarp for Organic Weed Control and Bed Prepping to learn more. 

3. Pest and Disease Control

Disruption of Pest Cycles

Did you know cover cropping can improve soil health and break pest life cycles simultaneously? It’s also an effective way to attract beneficial predators of your garden’s worst pests. Create an insectary by selecting the right cover crops, providing food for the insects, and letting nature do some pest control for you. 

• Plant buckwheat to attract ladybugs, hoverflies, and lacewings. In turn, they’ll help control tarnished bug and aphid populations. 
• Are you struggling with spider mites? Attract parasitic and tachinid wasps, which will prey on them by planting clovers. 
• Hairy vetch will bring minute bugs, parasitic wasps, and ladybugs to your yard to help with the tarnished plant bugs. 
• While marigolds aren’t the most common cover crop, their scent may keep away ants, knot root nematodes, tomato hornworms, cabbage worms, whiteflies, squash bugs, aphids, and larger pests like deer. 
• Rather than reaching for chemical pesticides, plant broadleaf mustard instead. It acts as a powerful biofumigant; while decomposing, it releases the byproduct isothiocyanates (ITCs), which help control soilborne pests and fungi. 

Related: Beneficial Insects for Gardens, Farms and Greenhouses

Disease Suppression

Cover crops alter the soil’s microbiology and strengthen its ability to fight off disease-causing fungi and bacteria. When combined with no-till gardening methods, vegetables grown directly into cover crops may experience lower fungal disease due to decreased splash up from the soil surface. 

• Decrease the risk of verticillium wilt by growing oats or winter rye alongside potatoes. 
• Reduce the chances of sclerotin stem rot and verticillium wilt by adding mustards alongside lettuce and cauliflower.
• Buckwheat serves as a breeding ground for beneficial insects, which will help decrease populations of cucumber beetles. Cucumber beetles carry the bacterial wilt-causing Erwinia tracheiphila in their guts. 

Before selecting cover crops to reduce disease risk, consider the fields' history, including past disease pressure, as sometimes, the risk can increase if not appropriately managed. Contact your local ag extension office agent for further assistance. 

Related: Boost Harvests with Companion Planting: Top Garden Pairings

4. Soil Erosion Prevention

Root Systems Stabilize Soil

Bare soil can erode from heavy rainfalls, dry out, and crack under the sun. To stabilize the soil, provide diverse root systems and lush foliage with cover crops. Growers on sloped land should consider cover cropping to avoid soil runoff. In a no-till system, roots remaining in the soil will continue to reduce runoff. 

Oats: Oats are a flexible and quick cover crop that can fill a late summer slot before you sow winter cover crops. They’ll effectively suppress weeds and uptake nitrates, recycling those nutrients for later use. 

Barley: Barley is great for cool-region growers and popular in cover crop mixes. Its incredible root system improves soil tilth, allowing for better drainage and reducing erosion. 

Oilseed, daikon, and forage radishes, or forage turnips: These deep-rooted vegetables are highly effective in breaking up compacted soils, creating aeration pockets underground, and decreasing water run-off. 

Cover Crops as Mulch

Living mulch works in place while growing to reduce erosion and compaction and improve soil fertility. Cover crops can serve as living mulch between plantings for a boost in fertility or in paths to keep weeds down and reduce erosion. Try white clover for a perennial living mulch to help reduce weed competition among annual weeds and your precious garden vegetables. 

When terminated and turned under, cover crops become effective green manure, adding organic matter (grasses), nutrients (buckwheat and mustard), and fixed nitrogen (legumes). 

How to convert cover crops to mulch:

• Establish a tall cover crop like winter rye. A good alternative is hairy vetch. 
• Allow it to reach the milk stage (winter rye only). This stage is essential so the plant doesn’t stand back up after crimping and continue growing. 
• Crimp it down flat to the soil surface. 
• Crimping can be done easily by laying a 2x4 on the bed and standing on it. Pick up the board and move it six inches further along and step on it again. Repeating this along the length of the bed will effectively break the stems and should prevent regrowth. 
• Cover the area with a tarp for a few weeks to allow some decomposition and allow allelopathy to slow. 
• Remove the tarp. 
• Plant summer crops like tomatoes, peppers, kale, and Swiss chard directly into the debris. 

The decaying rye will suppress weeds, help retain moisture, and, as it breaks down, add fertility and organic matter to the soil. 

5. Enhanced Water Retention

Moisture Conservation

Crops growing in the soil create a shade canopy over the soil surface, preventing evaporation and soil erosion. Terminated cover crop debris left on the surface continues to protect the soil surface and retain moisture. Plant debris incorporated into the soil adds organic matter, which offers the same benefits. 

Two cover crops effective in moisture conservation are hairy vetch and peas. Hairy vetch has deep roots, and its tall foliage becomes a thick, lush blanket that helps retain moisture and reduce weeds. Field and winter peas have robust root systems that allow water to infiltrate from the surface more efficiently and the soil to hold that water. Increasing the soil’s ability to hold onto water is critical to soil structure and improvement. 

Prevention of Water Runoff

Shifting climate has caused more unpredictable and extreme weather, such as heavy rainfall and strong winds, to become regular summer events growers must plan for. Hard rains can quickly cause soil compaction, erosion, and nutrient run-off. Preparing your soil for these events will keep your soil and nutrients where they belong. 

Soil covered with diverse plants and deep roots will absorb rain instead of allowing it to run off, causing a less dramatic outcome. A mix of sunflowers, radishes, fescue, crimson clover, and perennial ryegrass is an excellent choice to pinpoint water runoff issues. 

Using Cover Crops with Season Extension Methods

Row Covers and Frost Blankets

Using row covers and frost blankets may provide enough heat to ensure proper growth before a killing frost. The more established a cover crop is before winter, the more benefits it will provide. As plants grow, biomass, robust root systems, soil coverage, and future mulch increase. 

Hoop your cover crop plantings and cover them like your lettuce in the spring or basil in the fall. I’d argue their survival is more important than the food you grow to eat because they feed the soil! Read our article Frost Blanket: How to Use it and When for details on implementing this in your home garden.

Creating a Stale Seed Bed by Killing Cover Crop in Spring

How you terminate cover crops in the spring depends on the crop type. We like to mow down barley, hairy vetch, and cereal rye and then cover them with silage tarps to speed up the breakdown process. When you remove the tarp, simply hoe the debris, optionally broadfork, reshape your bed, and directly sow into it or add transplants. The biomass left behind can now serve as mulch, and the bed should be weed-free. 

FAQs

What are the best cover crops for beginner gardeners?

If you’re new to cover cropping, buckwheat is quick, beneficial, and excellent at attracting pollinators. Plus, it's easy enough to pull if it pops up somewhere around the garden. 

How long does it take for cover crops to improve soil health?

The sooner you incorporate cover crops, the sooner you will notice a difference in your soil health. While changes occur slowly, a study on trial farms as part of the Soil Health Partnership of the National Corn Growers Association shows a positive shift in active carbon, soil organic matter, respiration, and aggregate stability when cover crops were used. However, effects may take 3 to 5 years or more to be evident. 

Can cover crops be used in raised beds?

Cover crops effectively keep soil in raised beds fertile and refresh them after a season. For best results, have a solid plan for termination. 

When is the best time to plant cover crops in a home garden?

Timing depends on what crops are growing, the rotation plan, the climate, and whether or not you need to utilize the space this season after the cover crop or if it will remain in the soil through the winter. Planting in the spring, summer, or fall also depends on whether you experience killing frosts in your area and whether or not you want it to survive. 

How do I terminate cover crops before planting vegetables?

Cover crops can be hand-cut on a small scale or mowed, tarped, smothered, cut down, crimped, or turned under on a larger scale. Just remember you must leave the cut plant matter in the bed for the most benefit.