Using green manures in no dig gardening is hugely beneficial. It is a sustainable, affordable way to protect soil, increase biodiversity and add fertility to your garden.

People have been using green manures, often known as “cover crops” as part of soil health for millennia, but they were not widely available to home growers in the UK until relatively recently. Now available from most online seed companies and gardening stores, green manures are a thrifty, accessible way to grow great soil, and create a thriving plot.

What is a green manure?

A green manure is a living plant cover crop used in home gardens, allotments, market gardens and farms. Usually fast growing plants, they are grown to help protect soil, reduce weeds and increase soil fertility. They are a natural, organic way to increase biodiversity above and below the soil. 

No dig and green manures

I am often asked how green manures fit into a no dig gardening system. Don’t you have to dig them in? Thankfully the answer is: “absolutely not!” If you think about it, there’s no point doing something that benefits and helps to protect the soil, and then digging it all over, which destroys crucial soil structure, kills soil life and mycorrhizal fungi, creates more weeds and releases carbon stored in the earth into the air.

Instead, for no dig gardens choose green manures which either die during the winter, killed off by frosts and snow, or which are easy to cut down, leaving the roots in the soil.

Tall cover crops such as field beans, lupins and forage peas need to be cut before the bed is used for the next plantings. Cut at ground level, leaving the roots in the soil (this benefits the soil flora and fauna), and chop up the plant matter. Add this to the compost heap, or spread under perennials to rot down as a chop and drop mulch. Spreading it on annual veg beds in much of the UK  would create a slug habitat. This is not ideal for establishing young food crops, whereas in hotter drier climates where slugs are not an issue, it would be an ideal mulch for the beds. 

If you do accidentally sow a green manure that is more difficult to remove, such as forage rye, don’t despair! Simply cut it down (with a strimmer, lawnmower or suchlike) and cover with a sheet of light excluding mulch such as black polythene or thick card for a few weeks, to kill off the roots.

Green manures on an allotment plot

Mixed green manure seeds

Many seed companies offer green manure mixes. I avoid these, choosing separate specific varieties and making my own mix. This is because these usually contain rye which is much more difficult to kill off than other green manures. Always check mixed seed packets to see what they contain. Choosing separate varieties and making up your own combinations means that you can adapt each sowing to suit the environment in your garden. And it’s fun. 

Can you sow green manure between other plants?

Whether you can under-sow a green manure between veg and other plants depends on what they are, and where you are located (climate, soil type, what kind of pests are prevalent). Smaller plants could easily be out-competed by green manures, and it can be risky for plants which are susceptible to slug attack.

However during hot dry weather, a green manure can help to protect the soil and benefit the growing crops, by reducing evaporation of moisture from the bed. Like so much of gardening, it very much depends on your circumstances, the time of year and the weather.

I try to grow as much food as I can here, and maximise food production from each bed using interplanting. Also know as intercropping, this usually involves growing smaller ‘catch crops’ between larger plants. For this reason, I don’t use green manures in annual beds where I am intercropping because there is the risk of these green manures outcompeting my smaller food crops.

Leeks undersown with a mix of summer flowering green manures

Green manures work brilliantly between perennials and larger annual plants (unless intercropping). Sow under fruit bushes, alongside rhubarb, under trees, between brassicas once they are established, in herbaceous borders, under sweetcorn, between leeks – there are many possibilities to explore.

Every year I experiment with different combinations, to discover what works well. I sowed green manure in a newly created asparagus bed to increase biodiversity and protect the soil from weed seeds blowing in, choosing phacelia which would not compete with the establishing asparagus roots. This quickly covered the bed, the distinctive purple-blue flowers providing forage for insects and, during periods of extended dry weather, helped to protect the soil from moisture evaporation. 

Many market gardeners and farmers use green manures with annual veg with great success, using seed drills, brush cutters and crimping machines, which are not usually part of the home grower’s repertoire. At Oxton Organics in Warwickshire, market gardener Jayne Arnold uses an extensive range of green manures in her no dig beds, with great success.

A flourishing mix of green manures at Oxton Organics

Benefits of green manures

Green manures are incredibly beneficial for the garden. The advantages of using them include:

• Green manures improve soil fertility, bring up nutrients and minerals from the soil depths, and increase biodiversity above and below the soil.
• They protect soil from extremes of weather. They  help to keep nutrients from washing away during heavy rain. Green manures can help prevent soil erosion in windy places. They shade the ground and reduce water evaporation during dry weather.
• Green manures help to suppress weeds, forming a thick layer of plant matter on the surface of the soil making it less likely that weeds can germinate. Perennial weeds such as bindweed, brambles, horsetail (often also called mare’s tail)  or couch can still grow through green manures.
• Slug predators such as toads and black beetles enjoy the cool, damp ground cover green manures provide.
• Some green manures fix nitrogen in the soil – such as field beans, forage peas and vetch.
• Green manures can deter some pests and diseases. Brassicas undersown with trefoil, crimson clover or vetch can help to confuse flying insects such as cabbage white butterflies. Some research suggests that mustards can reduce wireworm, acting as a biofumigant.
• Allowed to flower, green manures such as phacelia, crimson clover and mustards provide forage for many creatures and attract beneficial predators into your garden.
• To further increase biodiversity, you can use two or more green manures together, such as tall growing field beans with an under sowing ground cover of crimson clover.
• Some green manures, such as field beans, are excellent for adding bulk to compost heaps, increasing your compost production. (See “field beans” below.)
• Deep rooting green manures (eg: radishes) can help break up heavy clay soil – but no dig does that anyway, naturally, by allowing soil life to thrive.
• Can help reduce the amount of compost you need for your beds.
• They are great for people wanting to use no or less animal products (eg: animal manures) in the garden, ideal for veganic growers.
• The small packet sizes make them a viable option for home and allotment growers, and they are affordable too.
• You can save the seeds every year, saving money.

Disadvantages of green manures

• In very damp weather, green manures can increase habitat for slugs and other creatures that enjoy munching on our veg.
• During a mild winter, green manures may create ideal conditions for slugs and snails to thrive, survive and breed. But as they also create a habitat for their predators, there should be a balance.
• If you practice soil rotation, you’ll need to take this into account in your garden plan. You may wish to avoid growing brassicas in a bed which has had overwintered mustards in, for example. 
• Avoid using mustards and other members of the brassica family as a green manure if you have club root on your plot.
• Some green manures such as hemp are currently not legal to grow in the UK without a licence from the Home Office. Do check your local regs!
• Some green manures are more difficult to get rid of, such as rye. Just avoid these
• Not a disadvantage of the green manures, but rather of bad advice. Unfortunately the advice on most green manure packets is to dig it in, which is a bit bonkers really as it’s much better for the soil and planet not to.

Long term green manures

Long term cover crops, such as white and red clover, are ideal for areas where perennials such as fruit bushes, trees or shrubs are growing. They are best avoided on annual beds, where they can compete with vegetables and make it difficult to sow.

An excellent weed suppressant, these living mulches also fix nitrogen from the air and provide habitat for a wide range of creatures, as well as vital forage for bees and other insects.

Cover crops reduce the need for compost

Usually I mulch my beds annually with around 1cm (1/2”) compost which feeds the soil and soil life, and helps to protect the beds too. It isn’t always possible to make or obtain enough compost to do this on all of my beds, and so I use green manures as part of my garden fertility routine, especially during the winter months when it helps to protect the soil against heavy rains and bad weather.

Organic market gardener Jayne Arnold has discovered that using green manures as part of her growing system has significantly reduced the need to use compost. She creates her own multi-species mixes using four different plant family groups, and within that 8-12 varieties, to maximise diversity. Each plant feeds a different set of soil microbes, significantly increasing soil biodiversity and health.

Jayne grows at Oxton Organics – find out more about her work here.

When to sow green manures

The sowing times vary according to variety. For overwintering, choose cover crops which with survive most of the wintry weather: mustards, field beans, winter tares (vetches) forage peas. Rye grass will also survive the winter, but as already explained this can be difficult for smaller scale growers to remove in the spring.

The rest can be sown any time from spring onwards, until September. Some such as field beans and forage peas can be sown later, during October and November (weather permitting!)

Phacelia

buckwheat

caliente mustard

Some green manure varieties

Caliente mustard

With biofumigant properties, this is an ideal green manure to sow in areas where potatoes are grown. It will overwinter and can be sown anytime from March – October

Field Beans

An ideal over winter green manure, they are edible too if allowed to mature. Use just like broad beans.

Crimson Clover

One of my favourites, for the stunning flowers it produces, it is much loved by bees. Sow from spring to late summer, it is killed by harsh winter weather. (Not to be confused with red clover, which is a perennial.)

Fenugreek

A fast growing cover crop, sown from March – August. A legume, it fixes nitrogen and produces white flowers which attract a variety of insects.

Forage Peas

Sown from September – November, this legume is one of the best over wintering cover crops, helping to suppress weeds. 

Buckwheat

A fast growing cover crop, buckwheat quickly out-competes annual weeds with a dense canopy of leaves and flowers.

Alfalfa

One of the longer lasting green manures, alfalfa can grow for a year or so, surviving winter if established from a late spring/early summer sowing. Cut 2-3 times a year to encourage fresh growth, the leaves can be used as a chop and drop mulch.

Lupins

With long tap roots, lupins help to bring up minerals from deep within the soil from a March-July sowing. They produce a gorgeous purple-blue flower and seed pods full of edible seeds. Cut at ground level once mature, and add the plant matter to the compost heap.

Phacelia

A real favourite with bees and hoverflies, this pretty green manure grows rapidly, helping to smother weeds. Sown from March to September, it can survive milder winters and self seeds with enthusiasm.

Fodder radish 

Sown from May to September, the radish dies back during cold winter months or can be cut at ground level. The flowers are tasty, and the roots help to break up compaction.

Leftover seeds from annual veg

Use up odds and ends from annual veg seed packets such as brassicas, annual edible flowers and salads as a green manure.

What about crop rotation?

Unless there is a specific reason to do so – such as club root or white rot – for most smaller scale growers crop rotation is not necessary. As we learn more about soil life it is becoming clearer that diversity is just as important below the soil as it is above, and that the soil flora, fauna and fungi thrive where there are many different kinds of root systems in the ground.

Green manures are one way of increasing this biodiversity, helping to create a healthy soil ecosystem.

Green manure suppliers in the UK

Most seed companies sell green manure seeds now, offering a lot of choice. Here are some brands I have used:

Real Seeds, Mr Fothergills, Chiltern Seeds, Sow Seeds

My New Book – The Productive Garden

Read more about using green manures, how to grow a productive garden year round and what to do with all of that lovely produce in my new book. Find out more here.

The Productive Garden: An essential guide towards self-sufficiency will be published in the US on March 24th and in the UK/internationally on March 26 and pre-orders are open.

Pre-orders for the UK are here
Pre-orders for the US are here
Pre-order signed copies from me here

Pre-orders are much more of a “thing” now than they were when my previous books were published. The pre-order stats can significantly help the success of a book, because they are used by online and high street stores to decide whether to stock the publication. Have you ever wondered how books get on best seller lists? Pre-orders are one way they accomplish this.

Thank you to everyone who has pre-ordered. Your support is really appreciated.

The Productive Garden is listed as a recommended read in the March issue of Gardens Illustrated magazine.