Cover Crop Benefits: How Cover Cropping Works

If you struggle with excessively weedy beds, compacted soil, poor water retention, or garden beds that seem to shrink in depth every year, you may want to integrate cover crops into this season’s garden plans. This simple concept involves planting specific grains, legumes, or broadleaf species to protect the soil during the off-season. 

Whether it’s winter or summer, this practice ensures you have living roots in the soil, even when you aren’t growing vegetables. Cover crops nurture soil fertility, smother weeds, add organic matter, and boost overall productivity while you take a break from gardening. Once you plant them, they do all the heavy lifting until you’re ready to terminate and start growing veggie crops again.

Rather than leaving soil naked and vulnerable during the off-season, these crops help growers mimic natural ecosystems that maintain living roots in the soil at all times. 

Here’s a deep dive into each of these well-researched benefits and how they help your garden flourish with less effort:

Suppress Weeds

As gardeners, weeds are the bane of our existence. Personally, I’ll do almost anything to reduce the amount of time I have to spend weeding. In exchange for less than an hour each season, I can sow, tend, and terminate crops that practically do the weeding for me.

Cover cropping suppresses weeds by quickly growing biomass to cover your beds. The clumps of fast-growing foliage crowd out weeds, leaving little to no space for new plants to germinate. This is especially important during winter and spring when the weather is cold and wet, but you can’t get your main crops into the ground yet.

If weeds are a major issue in your garden, choose grassy species that germinate and establish quickly after seeding. Research shows that grass cover crops suppress weeds more than their broadleaf or leguminous counterparts. Grass-family (Poaceae) types include oats, rye, wheat, and barley.

Remember, Mother Nature always wants to cover barren soil. That’s why weedy species like dandelions, thistles, and bindweed pop up so quickly! If you leave the soil naked, nature will “clothe” it quickly with weeds. Cover cropping is like a winter sweater or a spring hoodie; it keeps the soil cozy and covered so weeds can’t sneak in.

Covers Vacant Soil (Erosion Protection)

Cover crops are crucial for protecting your garden from erosion. Unless you grow crops year-round in rapid succession, you likely have chunks of time when your garden is bare. This is when it is most important to plant crops that can keep the soil covered until you plant your main crops again.

Have you noticed how barren garden beds seem to shrink over time? While some amount of soil sinking is natural, losing several inches of soil each season is not ideal. Soil is expensive to import and time-consuming to maintain, so you want to keep as much of it in your garden as possible. But if you leave your soil bare after each crop harvest, the vacant dirt will likely drift away in winter storms or spring rains.

Erosion is the process of soil particles blowing or washing away. In nature, erosion happens naturally over massive time spans, sometimes forming breathtaking landscapes like the Grand Canyon or Utah’s famous arches. 

However, erosion in your garden doesn’t yield as pretty of a sight: it can mean reduced yields, shrinking beds, muddy pathways, and an overall loss of productive space. On a massive agricultural scale, over 24 billion tons of fertile soil is lost every year due to erosion, essentially causing Dust Bowls all over the world.

If this seems dramatic or unrelated to your garden efforts, remember that anything happening on a large scale starts on a micro-scale. Ensure the soil stays where you want it— in your garden beds! If you notice dust blowing away from your garden on windy days or muddy streams flowing from your beds during rainstorms, you probably need plants to anchor the soil in place.

Improve Soil Water Management

Cover crops moderate soil moisture. A long-term study at the University of Nebraska-Lincoln found that they directly improve water balance and reduce evapotranspiration, making water more available to crops planted afterward.

Retain Moisture

In dry seasons, this benefit comes primarily from the residue cover that prevents UV rays from hitting the soil and drying it out. The foliage is like a natural sunscreen for the soil, and it keeps working as mulch even after you terminate it! 

You never want to leave bare soil exposed to the sun, as this can rapidly degenerate the microbial activity and dehydrate the upper soil layers, creating more susceptibility to dusty erosion in the wind.

Improve Infiltration

In wet climates, rainfall is a major cause of erosion and nutrient leaching. As raindrops fall or ice melts, the microscopic impact washes soil particles away. As those particles sink into muddy puddles, little gullies, or trickling streams of water, they carry the valuable organic matter and plant nutrients you worked so hard to build. 

Cover crop roots anchor the soil in place to prevent muddy runoff from accumulating in your pathways. The active water uptake by these plants, combined with their aerating roots, ensures your beds don’t get super soggy or waterlogged. In other words, plants improve water infiltration. Moisture naturally drains through the soil profile without washing away valuable nutrients or puddling up on the surface.

This results in more consistent water availability for the plants you grow afterward. You won’t have to worry as much about extremes (like dusty dryness or waterlogging) because soil with more organic matter (from the cover crop roots and foliage) holds and drains water more efficiently.

Nurtures Soil Microbes

Although we do a lot of human labor in our gardens, microorganisms are the hardest workers you can ask for. Soil microbes like beneficial bacteria, fungi, protozoa, and nematodes (collectively called the soil microbiome) are extremely important for plant nutrient cycling, immunity, and overall health. 

Thankfully, these microscopic creatures don’t ask for much in exchange for their 24/7 labor. Like most of us, they only need a place to live, water to drink, oxygen to breathe, and food to eat. Cover cropping provides all four!

Nurture the Microbiome

Cover crops nurture the soil microbiome by maintaining soil habitat when your main veggies or fruits aren’t growing. The roots of cover crop plants create millions of little channels in the soil. Each channel is another place where air, water, and minerals can accumulate.

Plants bring oxygen into deeper layers of soil that may have previously been compacted or anaerobic (without oxygen). Many beneficial microorganisms thrive in oxygenated environments, whereas many pathogenic microbes (like the fungi that cause root rot) tend to take hold in anaerobic environments.

Cover cropping provides food for microbes by adding biodegradable matter to the soil. Each time you terminate a cover species, the roots, stems, and leaves become fuel for microbial growth, much like in a compost pile. Moreover, leguminous crops like vetch, fava beans, and clover create symbiotic relationships with nitrogen-fixing bacteria that create homes in their root nodules.

While we are often bombarded with the image of perfectly uniform, exposed, brown soil, cover-cropped or mulched soil is the secret to gardening success. If you leave cover crop residues on top of the bed like mulch, the decomposing foliage provides a shady, moist area for microbes to build a thicker upper layer of loamy topsoil. At the same time, the roots can break down beneath the surface, creating the rich, luscious soil you dream of sinking your hands in!

Boosts Fertility

Scientific studies show that cover crops reduce fertilizer needs and improve crop yields by boosting nutrient availability in the soil. Nitrogen-fixing legumes like alfalfa, winter peas, hairy vetch, and clover are popular for improving soil fertility. They work with symbiotic bacteria to transform nitrogen in the air into plant-available nitrogen in the soil. In other words, when you plant a leguminous cover crop, you get an almost free source of fertilizer for the following crops.

To enjoy the most fertilizer benefits, it’s important to terminate plants at the proper time. Generally, the best time to kill the cover crop is when it is still green, pliable, and just starting to flower. At this stage, it has the highest available nitrogen and breaks down more rapidly. If you wait until the cover crop goes to seed or turns brown, the carbon-to-nitrogen ratio will flip, and it becomes more carbon-rich. This is still good for your soil, but it won’t add the same rapid nitrogen-boosting fertility for the next crop.

Cover crops grown specifically for nutrient additions are sometimes called green manure. This requires incorporation into the soil or leaving residues on top of the bed. Crimping or tilling are common ways to terminate and reintegrate the cover crop into the bed. However, tillage poses other issues with soil disturbance.

If you want to boost fertility, I recommend using pruners, a mower, or a scythe to chop down all above ground biomass, then leave it in place to decompose for a few weeks before planting your veggies.

Improves Soil Structure

Soil structure describes the physical particles of sand, silt, and clay that assemble into aggregates or clumps. The patterns of these “clumps” create intricate underground structures, similar to a belowground city. Just like buildings, roads, or sewer lines are vital infrastructure for a human city, the structure of soil aggregates is crucial for providing habitat for microorganisms, reservoirs of water, hubs of mineral nutrients, and oxygen-rich spaces for plant roots to dig in.

The main way cover cropping helps to improve soil structure is by reducing compaction. Compacted soil lacks structure because it has been tilled, compressed, or otherwise damaged into a hard, concrete-like surface that makes it difficult for fragile veggie crops to penetrate with their roots. Soil with poor structure tends to cause problems like stunted plants, waterlogging, root rot, and other plant diseases.

Deep-rooted crops like lupine, alfalfa, clover, and radishes break up compaction by digging deep into the lower layers. The root channels bring oxygen and water, aiding in aggregation that ultimately helps rebuild the thriving underground “city” we discussed above.

Tillage daikon radish is the best cover crop for breaking up compaction. The giant bulbous tap roots reach nearly 3 feet in the soil, creating huge channels for microbes, water, and crop roots to make a new home. The lateral roots also grow outward to break up hard layers and invite oxygen into smaller crevices.

Adds Organic Matter

Soil organic matter, or humus, is the most important component of healthy garden soil. This decomposed plant and animal matter is like a nutrient-dense sponge that improves the soil’s ability to hold onto water and minerals. Generally, soils with higher levels of organic matter are more productive and more microbially rich, yielding healthier, more abundant crops.

Plants add organic matter both above and below the soil level. Belowground, the roots add biomass, which creates habitat and food for microbes (particularly fungi). It’s important to leave cover crop roots intact under the soil so they can serve this valuable function as they decompose. 

Above-ground crops are excellent at turning sunlight, water, and spare soil nutrients into abundant leaves and stems. Once terminated, this foliage is decomposed by microorganisms to create more organic matter in the soil. The biomass can be incorporated into the soil with a broad fork, rototilled (less ideal due to soil disruption), or mowed and left on top of the soil surface to break down as mulch.

Research shows that legume cover crops can improve organic matter by 8% to 114%, while non-legumes like grasses and brassicas can increase organic matter levels from 4% to 62%! 

To reap the best of both worlds, I mix the two categories with blends like oats with peas or combining rye and vetch. To ensure maximum plant biomass growth (which creates the most organic matter), seed fall cover crops at least 4-5 weeks before your expected first frost date. This enables the crop to get fully established before frigid weather sets in.

Aid Crop Rotation

Crop rotation is the art and science of rotating different plant families around to disrupt the cycles of pests and diseases. Cover crops make rotation planning easier by inserting an unrelated plant into a bed over the winter so you can replant it with a similar crop again in the spring.

For example, many pathogens and insects attack brassicas (Brassicaceae or cole crops) like broccoli, cauliflower, Brussels sprouts, and radishes. To interrupt these cycles, you may rotate your brassica bed with a fall cover crop like oats (Poaceae or grass family) to confuse pests and prevent fungal diseases from further propagating their spores. In the spring, it may be safe to plant turnips or kale in that bed once again.

Similarly, you may have an amazing tomato (Solanaceae or Nightshade family) bed that you have worked hard to amend for vigorous tomatoes. If you grow tomatoes in that bed in the summer but have a few issues with blight or hornworms, you may want to plant peas (Fabaceae or legume family) and oats (Poaceae or grass family) over the winter to interrupt those cycles. Perhaps you plant a quick round of spring greens like arugula (Brassicaceae), and then you can safely plant peppers or tomatoes in the same bed for the following season.

Unique crops like buckwheat (Polygonacaeae family) or phacelia (Boraginaceae) have very few relatives in the vegetable and fruit gardening world, making them ideal candidates for crop rotations.

Provide Compost Input

If you don’t want to leave your cover crop to decompose in place, you can always cut away the aboveground foliage and take it to the compost. For small yards and gardens without a ton of kitchen scraps or yard waste, it’s an excellent source of biodegradable plant matter for your compost.

As a general rule of thumb, young and fresh cover crop foliage harvested right around flowering counts as a “green” or nitrogen-rich compost input, much like grass clippings or vegetable scraps.

Brown and mature cover crop foliage harvested around the time of seedhead formation counts as a “brown” or carbon-rich compost input. Ideally, you should terminate a cover crop before seed maturity so your cover crop doesn’t become a weed. Winterkill crops also fall in this category when they turn to straw-like material after a frost has killed them.

How Cover Cropping Works: 6 Simple Steps

To enjoy all the tremendous benefits, it’s helpful to understand how successful cover cropping works in a real-life garden. While it may require trial and error for your specific climate and bed setup, these six steps will set you up for success.

Proper Timing is Key

The perfect window for cover cropping is after your main crop is harvested but before any harsh weather sets in. In the northern fall, this means establishing the planting at least 4 to 5 weeks before your first frost. In the southern summer, you may need to plant in the cooler spring weather or choose a heat-tolerant species.

You can technically grow cover crops at any time of year when a garden bed is fallow. In a particularly weedy, compacted, or poor-performing bed, you may want to skip a season and focus on soil health. Whatever you choose, be sure you properly time your planting based on the season:

• Summer: Seed immediately after your spring vegetable harvest
• Fall/Winter: Seed 4-5 weeks before expected fall frost 
• Spring: Seed right around the last frost date

Select Suitable Species

The right cover crop for your garden depends on your goals, climate, and seasonality. You can also blend different crops if they have similar growth requirements and maturity rates. When in doubt, choose a pre-made cover crop blend from a local seed company that has made selections adapted to your region.

Best for Improving Fertility

If your primary goal is to boost nutrient availability, these leguminous crops work with symbiotic bacteria to transform nitrogen from the atmosphere into plant-available nutrients:

• Hairy Vetch (Vicia villosa)
• Red Clover (Trifolium pratense)
• White Clover (Trifolium repens)
• Crimson Clover (Trifolium incarnatum)
• Austrian Winter Pea (Pisum sativum subsp. arvense)

Best for Breaking Up Compaction

Hardpan or compacted soil requires hefty, deep roots to dig deep in the soil and help improve structure. These species have deep taproots and lots of lateral roots that reliably anchor into even the heaviest clay soil:

• Winter Rye (Secale cereale)
• Annual Ryegrass (Lolium multiflorum)
• Buckwheat (Fagopyrum esculentum)
• Lupin (Lupinius spp.)
• Daikon Radishes (Raphanus sativus)
• Tillage Radish (Raphanus sativus var. longipinnatus)

Cold-Hardy Types

Northern gardeners need cover crops that will stay standing through frigid weather and snow. These cold-hardy options typically last until a spring termination:

• Winter Rye (Secale cereale)
• Crimson Clover (Trifolium incarnatum)
• Austrian Winter Pea (Pisum sativum subsp. arvense)
• Winter Wheat (Triticum aestivum)
• Hairy Vetch (Vicia villosa)

Warm Weather (Frost Kill) Types

Frost-killed or winterkill cover crops have the advantage of less work. Since these tender species are killed by frosty weather, you don’t need to worry about terminating them; they simply form a nice mulch mat on the soil surface. Many also provide pollinator habitat when flowering.

• Buckwheat (Fagopyrum esculentum)
• Sorghum-Sudangrass (Sorghum bicolor x Sorghum sudanense)
• Sunflower (Helianthus annuus)
• Cowpeas (Vigna unguiculata)

Plant Densely

When seeding cover crops, a broadcast method is typically best. You can use a broadcast seeder or your hands to distribute the seeds evenly and densely. Depending on the species, you want them to fall approximately 1-3” apart, ensuring a thick stand that will smother weeds and competitors.

Management

Most cover crops require modest irrigation to get established, but once the seeds take off, they are virtually maintenance-free. However, it’s important to regularly check your beds to ensure no pests or diseases have overtaken the crop, as this could completely reverse their benefits and cause more problems in the future.

Terminate Properly

Termination is killing the cover crop so it can decompose in the soil, mulch the soil surface, or get added to your compost pile. My favorite way to terminate is simply planting winterkill species that naturally die off through the winter, leaving behind a nice fluffy mulch to decompose through spring. 

If you are growing cold-hardy species, you will need to kill them before the set seed (after all, you don’t want your cover crop to become a ryegrass lawn in your garden bed!)

Termination options include:

• Flail Mowing (leave roots and residues in place)
• Scythe (an old-fashioned non-mechanical cutting tool)
• Pruners or loppers (only viable on a small scale)
• Rototilling (not recommended due to soil disruption)

If your cover crop has just started to form seedheads, don’t worry! You still have time to terminate it before the seeds mature. If you forget to terminate the crop altogether, you may need to cover the bed with a tarp to germinate and smother the dropped seeds so they don’t become weeds in your next veggie planting.

Document and Adapt

Like with all garden methods, it’s best to document your cover cropping experiments to ensure you can avoid or replicate different results in the future. 

Remember to record your:

• Cover crop planting date
• Seasonal weather
• Periodic growth intervals (height, color, performance)
• Termination date and method