Green manures might sound like an old-fashioned gardening technique, but they’re making a comeback for good reason. These living fertilisers can transform your garden’s health while reducing your reliance on expensive bought-in composts and fertilisers. Whether you’re a seasoned gardener or just starting out, green manures offer a simple, natural way to improve your soil and boost your harvests.
Green manures work by harnessing the power of plants to feed your soil naturally. Instead of leaving beds empty between crops, you sow fast-growing plants that will later be dug back into the earth. This ancient practice mimics nature’s own way of maintaining fertile soil, and the results speak for themselves.
The best part? You don’t need any special equipment or expensive materials. With just a packet of seeds and some basic knowledge, you can start improving your garden’s soil health right away. Let’s explore how green manures work and why they deserve a place in every British garden.
What Are Green Manures?
Green manures are plants grown specifically to benefit the soil rather than for harvest. You sow them on vacant ground, allow them to grow for a period of weeks or months, then dig them back into the soil while they’re still green and full of nutrients. This process adds organic matter, improves soil structure, and provides a slow-release source of plant food.
Think of green manures as a cover crop with benefits. While they’re growing, they protect your soil from erosion, suppress weeds, and can even attract beneficial insects. Once you incorporate them into the soil, they break down to release nitrogen, phosphorus, potassium and other essential nutrients your future crops will need.
The practice works because growing plants capture nutrients from deep in the soil and concentrate them in their leaves and stems. When you dig these plants back in, you’re essentially recycling those nutrients and making them available in the top layer where your vegetable roots can access them.
Why Should We Use Green Manures?
Green manures offer a sustainable solution to several common gardening challenges. They reduce the need for shop-bought fertilisers and soil improvers, helping you garden more economically and with less environmental impact.
Your soil structure will improve dramatically with regular use of green manures. The organic matter they provide helps heavy clay soils drain better while helping sandy soils retain more moisture and nutrients. Earthworms love the fresh organic matter, and their activity further improves soil structure and fertility.
From a practical standpoint, green manures make efficient use of your garden space. Rather than leaving beds empty and prone to weed invasion, you can grow something beneficial that requires minimal care. Many green manures are also attractive plants that can enhance your garden’s appearance during quieter growing seasons.
Advantages of Green Manures
Soil Health Improvement
Green manures dramatically increase soil organic matter content. This organic matter improves soil structure, creating better drainage in heavy soils and improving water retention in light soils. The result is soil that’s easier to work and more hospitable to plant roots.
Natural Fertilisation
Leguminous green manures like clover and lupins fix atmospheric nitrogen through their root nodules. This nitrogen becomes available to subsequent crops when you dig the plants in, reducing your need for nitrogen fertilisers.
Weed Suppression
A thick carpet of green manure plants prevents weed seeds from germinating by blocking light from reaching the soil surface. This natural weed control saves you hours of hoeing and weeding later.
Pest Management
Some green manures can help break pest and disease cycles. For example, mustard family plants release compounds that can reduce soil-borne pests, while flowering green manures attract beneficial insects that prey on garden pests.
Erosion Protection
Green manures protect bare soil from wind and rain erosion. Their roots also help hold soil particles together, preventing valuable topsoil from washing away during heavy rain.
Disadvantages of Green Manures
Timing Requirements
Green manures need careful timing to be effective. You must allow enough time for them to establish and grow before digging them in, which can delay your next crop planting. Poor timing can result in woody stems that are slow to decompose.
Space Competition
While green manures are growing, that ground isn’t available for food crops. This can be challenging in smaller gardens where every square metre counts for vegetable production.
Initial Nutrient Lock-up
Fresh green material temporarily ties up nitrogen as it decomposes. This means there might be a short period when less nitrogen is available to your crops immediately after digging in the green manure.
Variable Results
Success with green manures depends heavily on weather conditions, soil type, and timing. Dry spells can prevent proper establishment, while overly wet conditions can cause some green manures to become diseased.
When Should We Sow Green Manures?
Spring Sowing (March to May)
Spring is ideal for fast-growing green manures like mustard and buckwheat. These can be sown on ground that won’t be needed for main crops until mid-summer. Spring sowings work particularly well before planting brassicas, as you can dig in the green manure 4-6 weeks before planting.
Summer Sowing (June to August)
Summer sowings work well for winter cover. Crimson clover and winter field beans can be sown in late summer to provide ground cover through winter and early spring growth to dig in before your main plantings.
Autumn Sowing (September to October)
Autumn is perfect for hardy green manures like winter tares and grazing rye. These will establish before winter, provide ground cover during the cold months, and be ready to dig in during spring soil preparation.
Seasonal Considerations
Always check your local climate conditions. In northern Britain, sow earlier to ensure establishment before winter. In milder southern areas, you have more flexibility with sowing dates.
How Do We Use Green Manures?
Soil Preparation
Prepare your seedbed just as you would for any crop. Remove weeds, rake the soil to create a fine tilth, and ensure good drainage. Most green manure seeds are small and need good soil contact to germinate successfully.
Sowing Techniques
Broadcast seeds evenly across the prepared area at the recommended rate. Rake lightly to cover seeds with a thin layer of soil. Water gently if conditions are dry, but most green manures establish well with natural rainfall.
Growing Period
Allow your green manure to grow for 8-12 weeks, depending on the species and season. The key is to dig them in while they’re still soft and green, before they become woody or set seed.
Incorporation Method
Dig green manures into the top 15-20cm of soil using a spade or rotavator. Chop the plants roughly as you work to speed decomposition. Don’t worry about burying every piece completely—some surface material is fine.
Waiting Period
Allow 2-4 weeks between digging in your green manure and planting your next crop. This gives the organic matter time to start decomposing and prevents any temporary nitrogen lock-up from affecting your vegetables.
The 10 Most Popular Green Manures for UK Gardens
1. Crimson Clover (Trifolium incarnatum)
This attractive legume produces brilliant red flowers and fixes significant amounts of nitrogen. Sow from April to September for autumn flowering or August for spring colour. Crimson clover works well in most soil types and provides excellent ground cover. It’s particularly beneficial before nitrogen-hungry crops like brassicas and sweetcorn. The main disadvantage is that it can struggle in very wet or very dry conditions.
2. Mustard (Sinapis alba)
Fast-growing mustard is perfect for short-term ground cover. It can be ready to dig in just 6-8 weeks after sowing, making it ideal for quick soil improvement between main crops. Mustard has natural pest-deterrent properties and works well in most soil types. However, avoid using it before or after brassica crops as it’s in the same family and can harbour similar pests and diseases.
3. Winter Field Beans (Vicia faba)
These hardy legumes survive British winters and provide substantial organic matter and nitrogen fixation. Sow from September to November for spring digging-in. Winter field beans work particularly well on heavy clay soils and provide good weed suppression. They can grow quite tall, so they’re not suitable for very exposed sites where they might blow over.
4. Buckwheat (Fagopyrum esculentum)
This fast-growing annual produces masses of white flowers beloved by bees and beneficial insects. Buckwheat establishes quickly and can be ready to dig in within 10 weeks of sowing. It’s excellent for improving phosphorus availability in soil and works well on poorer soils. The downside is that it’s not frost-hardy, so it’s only suitable for summer growing in most of Britain.
5. Winter Tares (Vicia villosa)
Also known as hairy vetch, winter tares are excellent nitrogen fixers that survive harsh British winters. They produce attractive purple flowers in spring and can fix up to 200kg of nitrogen per hectare. Winter tares work well on most soil types and provide excellent ground cover. They can sometimes be slow to establish and may need protection from pigeons when young.
6. Phacelia (Phacelia tanacetifolia)
Often called “bee bread,” phacelia produces stunning blue-purple flowers that attract beneficial insects throughout the summer. It’s fast-growing, establishes easily, and improves soil structure with its extensive root system. Phacelia works well on most soil types and is particularly good for attracting pest predators. However, it’s not frost-hardy and needs to be sown after the last frost in spring.
7. Grazing Rye (Secale cereale)
This hardy grass provides excellent winter ground cover and adds substantial organic matter when dug in. Grazing rye has an extensive root system that improves soil structure and scavenges nutrients from deep in the soil. It’s particularly useful on light, sandy soils where it helps prevent nutrient leaching. The fibrous nature means it can be slower to decompose than other green manures.
8. Red Clover (Trifolium pratense)
A perennial legume that can provide benefits for multiple seasons if allowed. Red clover fixes substantial amounts of nitrogen and produces attractive purple-red flowers. It’s drought-tolerant once established and works well on most soil types. Red clover can persist for several years, which is beneficial for long-term soil improvement but may not suit vegetable gardens where annual turnover is needed.
9. Italian Ryegrass (Lolium multiflorum)
This fast-establishing grass provides quick ground cover and substantial organic matter. Italian ryegrass has an excellent root system for improving soil structure and is particularly good on compacted soils. It establishes quickly and can be sown at most times of year. However, as a non-legume, it doesn’t fix nitrogen and may actually compete with subsequent crops for this nutrient if not properly managed.
10. Trefoil (Medicago lupulina)
Also known as black medick, trefoil is a small clover-like legume that fixes nitrogen and tolerates poor, dry soils. It produces small yellow flowers and works well where other legumes might struggle. Trefoil is particularly useful on chalky or sandy soils and provides good ground cover. It can be slower to establish than other options and may not provide as much bulk organic matter as larger green manures.
Making Green Manures Work for Your Garden
Success with green manures comes down to choosing the right plant for your conditions and timing. Start with easier options like mustard or crimson clover to gain experience before trying more challenging species.
Consider your soil type when selecting green manures. Heavy clay soils benefit most from plants that improve drainage and structure, while light sandy soils need green manures that add substantial organic matter and improve water retention.
Plan your green manure sowings alongside your main crop rotations. This forward thinking ensures you always have something growing to benefit your soil, even when beds aren’t producing food.
Remember that green manures are just one part of good soil management. Combine them with compost addition, minimal digging, and crop rotation for the best results.
Transform Your Garden Naturally
Green manures offer every gardener an opportunity to work with nature rather than against it. These living soil improvers cost little to establish but provide lasting benefits that will enhance your garden for years to come.
Start small with one or two beds this season. Choose a simple, fast-growing option like mustard or buckwheat to see immediate results. As you gain confidence and experience, you can expand your use of green manures and experiment with different species.
Your soil—and your future harvests—will thank you for making this investment in natural soil health. Green manures prove that sometimes the best gardening solutions are the simplest ones.
Further Reading: Transforming Your Compost into Potting Mix, Homemade Fertilisers for Your Garden, How to Protect Your Soil in Winter, How and Why to Use Green Manures in Your Garden
For Daily Inspiration, Follow Us on Instagram💚
