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Boost Soil Health with Green Manure As A Cover Crop Over Winter
As well as using Strawberries As Ground Cover we use Green manure, also known as cover crops, across the Autumn and Winter months, this plays an essential role in sustainable gardening practices, particularly in winter. These crops help prevent soil erosion, suppress weeds, improve soil structure, and enhance fertility during the months when gardens or fields may otherwise lay fallow.
By planting cover crops like field beans, crimson clover, birdsfoot trefoil, and forage peas, you can naturally enrich your soil, preparing it for the growing season ahead. These are the 4 we are using this year, having used crimson clover for years, we added field beans to our edible crops last year for a harvest in Spring and birdsfoot trefoil grew naturally under one of our fruit trees so we’ve decided to add it in under them all this time and forage peas are new to us this year so follow along on our socials to see what happens with them.
Why Use Green Manure in Winter?
Over winter, when the soil would otherwise be exposed to the elements, green manure serves as a living blanket. It protects the soil from erosion caused by wind and rain, maintains its structure, and encourages healthy biological activity. Green manure crops also fix nitrogen in the soil, a crucial nutrient for plant growth, while their roots create channels that improve water infiltration and aeration.
By the time spring arrives, these crops can be chopped and dropped back into the soil (or left to decompose naturally), releasing stored nutrients and organic matter. This practice builds up soil fertility, reduces the need for chemical fertilisers, and supports healthier plants, all while working in harmony with nature.
What Is A Nitrogen Fixing Plant?
A nitrogen-fixing plant is a plant that has the unique ability to convert nitrogen from the air into a form that plants can use, which is essential for healthy plant growth. These plants form a symbiotic relationship with soil bacteria, particularly rhizobia, which live in nodules on the plant’s roots. The bacteria capture nitrogen gas (N₂) from the atmosphere and convert it into ammonia (NH₃), a form of nitrogen that can be absorbed by plants.
Nitrogen is a crucial nutrient for plant growth, as it is a key component of chlorophyll (for photosynthesis) and proteins. While nitrogen is abundant in the atmosphere, most plants cannot directly utilise nitrogen gas, making nitrogen-fixing plants highly valuable in ecosystems and agriculture.
Common examples of nitrogen-fixing plants include legumes such as peas, beans, clover, and alfalfa. Nitrogen fixing plants are often used as cover crops or green manure to naturally replenish nitrogen levels in the soil, reducing the need for chemical fertilisers and promoting sustainable practices. This process enriches the soil, benefiting both the nitrogen-fixing plants and surrounding crops.
Here’s a closer look at four cover crops we use around our garden for winter: field beans, crimson clover, birdsfoot trefoil, and forage peas.
Field Beans (Vicia faba)
Field beans are one of the most popular winter cover crops due to their hardiness and nitrogen-fixing abilities. As a legume, field beans form a symbiotic relationship with nitrogen-fixing bacteria in their root nodules, drawing nitrogen from the atmosphere and storing it in the soil. This will give you an extra food crop in late Spring time too, field beans are smaller and less bitter than broad beans.
Benefits: Field beans are particularly well-suited for cold climates, making them an excellent choice for winter cover, especially in Scotland. They grow quickly and are very effective at preventing soil erosion, thanks to their robust root system. Additionally, they add significant organic matter when incorporated back into the soil.
How to Use: Field beans are typically sown in late autumn and allowed to grow through the winter. Come spring, they can be cut down and incorporated into the soil as green manure, or you can allow them to flower for pollinators before chopping them in.
Crimson Clover (Trifolium incarnatum)
Crimson clover is another legume known for its nitrogen-fixing properties, and it’s an attractive addition to any winter garden with its bright red flowers. While often grown for its ornamental value in the spring, crimson clover is an excellent winter cover crop that improves soil fertility and attracts beneficial insects.
Benefits: Crimson clover helps reduce soil erosion, improves soil structure, and boosts fertility by fixing nitrogen. Its lush growth also smothers winter weeds, preventing them from taking hold.
How to Use: Sow crimson clover in early autumn, giving it time to establish before the first frosts. In spring, the plants can be mowed or cut before flowering and incorporated into the soil, adding valuable nutrients.
Birdsfoot Trefoil (Lotus corniculatus)
Birdsfoot trefoil is a hardy, perennial legume often used as a cover crop. It thrives in poor, compact soils, making it a great option for regenerating areas that may have been depleted by previous crops. Its ability to fix nitrogen makes it beneficial for improving soil fertility over time.
Benefits: Birdsfoot trefoil not only adds nitrogen to the soil but also helps with soil compaction. It has a deep taproot system that breaks up compacted soil, improving drainage and root penetration for future crops. Additionally, its flowers are highly attractive to pollinators, encouraging biodiversity.
How to Use: Plant birdsfoot trefoil in early autumn. While it may not grow as quickly as other cover crops, it provides excellent long-term benefits to the soil and can be left to establish over multiple seasons. In spring, it can be mowed or tilled under.
Forage Peas (Pisum sativum subsp. arvense)
Forage peas are another legume used as a cover crop to fix nitrogen and protect soil over winter. They grow rapidly in cool weather, again ideal for Scottish weathers and are highly effective at suppressing weeds, making them an ideal green manure crop for early winter planting.
Benefits: Forage peas excel at adding nitrogen to the soil, while their dense foliage covers and protects the soil surface. This crop also prevents erosion and provides a rich source of organic matter when incorporated into the soil in spring. Peas also encourage beneficial microbial activity in the soil, enhancing overall soil health.
How to Use: Sow forage peas in early autumn for winter cover. Once spring arrives, they can be cut down and mixed into the soil to enrich the ground with nutrients and organic matter. Their quick growth and ability to fix nitrogen make them an excellent green manure crop for most soils.
Incorporating Green Manure into Your Garden
To get the best results from green manure, sow these cover crops in autumn after your main crops have been harvested. Each crop offers unique benefits, so choosing the right one depends on your garden’s specific needs.
If your soil is compacted, birdsfoot trefoil can help break it up.
For nitrogen fixation and rapid growth, field beans and forage peas are excellent options.
For a balance of nitrogen fixation, weed suppression, and pollinator support, crimson clover is a beautiful and beneficial choice.
Once spring arrives, you can either mow down, chop and drop or chop and mix these crops into the soil, depending on your gardening methods. Allow the organic matter to break down for a few weeks before planting your spring crops, ensuring the nutrients are fully available to nourish your soil.
Using green manure as a cover crop over winter is a highly effective way to improve soil health, fertility, and structure. Crops like field beans, crimson clover, birdsfoot trefoil, and forage peas offer numerous benefits, from nitrogen fixation to weed suppression and erosion control. By incorporating these cover crops into your winter garden, you’ll ensure your soil is ready for the growing season, naturally enriched and protected for the months ahead.
Green Manure: Field Beans VIDEO REEL
Happy Gardening!
Katrina & Clayton and family live in East Ayrshire and share their daily life in the garden on instagram. They practice permaculture principles in the garden, reducing & repurposing waste whenever they can. Katrina shows how home educating in nature has helped Clayton thrive.
Clayton Completed The 2 Grow and Learn Courses with the Royal Caledonian Horticultural Society. He is Autistic, Non Verbal & has been Home Educated since 2018. Katrina & Peter hold their PDC & PDC PRO Permaculture Design Course from Oregon State University
They featured on BBC Beechgrove Gardens Ep23 2022 and returned in 2023 for an update,Katrina & Clayton are also columnists for ScotlandGrows Magazine, Guest Blog for Caledonian Horticulture as well as working with Gardeners’ World Magazine and many other brands.
They are also Author of the new children’s book series: Clayton’s Garden Journey: A Story of Autism and Gardening. Topics on Growing, Harvesting, Sowing & Composting and 108 Page Weather and Seasons Weekly Gardening Record Book available on Amazon and Kindle. Listen in on our Guest Podcasts to learn more about us.
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