by Sally Morgan
To convert existing vegetable beds to no-dig, all you need to do is add a layer of compost in autumn. Come spring, the compost will have been mixed in by the action of worms and other soil life. Any weeds that appear can be pulled or hoed off. You’ll need to hoe regularly to kill weed seedlings, or, if the weeds have got away, smother them with some mulch. The only time you need to move any soil is to make a hole for planting.
Once the crops have been cleared, we spread a thin layer of compost over our no-dig beds.
Pros and cons of no-dig
The no-dig method has many advantages:
It protects the soil structure.
It creates a soil with a rich, friable surface, which is less likely to cap and so force water to run off.
Moisture loss is reduced.
Weed seeds are not brought to the surface to germinate.
It helps to create a rich soil life, especially in the case of worms, which are not disturbed by digging.
It allows the soil to be worked on all year round.
There is no need for back-breaking digging.
But also some disadvantages:
Soil pests are not exposed to predators and cold weather.
It doesn’t deal with compaction or hard pans.
It takes longer to clear the ground of weeds.
The soil can take longer to warm up in spring.
Some people miss the therapeutic benefits and exercise associated with digging.
Chapter THREE
Soil fertility & crop rotations
Over time, the removal of crops from the land slowly depletes the soil minerals, especially phosphorus, so you need to add nutrients in order to keep your soil healthy. Adding nutrients in the form of organic matter also helps to support more soil organisms, which are important for making nutrients available to plants.
It is particularly important to look after the soil on your heavily cropped vegetable beds and in the polytunnel or greenhouse, where year-round cropping can take a heavy toll. Organic matter can be added as compost or manure, as well as by growing green manures. Compost in particular is key to a healthy soil, and this chapter describes the composting process and methods in detail. It also discusses crop rotations: the system of growing crops in different beds from one year to another, rather than in the same bed year after year. This traditional approach has long been used to prevent the build-up of disease and pests.
Feeding the soil
It’s very easy and tempting just to add artificial fertilizers to your soil to provide nutrients. Artificial fertilizers contain nutrients in a form that is readily available to plants, for example as nitrates, so when they are added to the soil they are taken straight up by the plant roots, bypassing the soil completely. It’s no surprise that over time, soil organisms and soil organic matter decrease and the soil becomes simply a medium to anchor the plant roots. As a result, it becomes necessary to add artificial fertilizer every year.
A much better way is to feed the soil itself, by adding organic matter. Growing green manures – plants grown as a ground cover and later incorporated into the soil – is also beneficial. These all provide food for soil organisms, especially the decomposers such as bacteria and fungi. There are other benefits too: a soil rich in organic matter will retain more water and nutrients and have a rich and diverse soil food web, making nutrients available to plants and helping to suppress disease.
All crops take up nutrients from the soil as they grow, so those nutrients must be replaced.
Using composts and manures
You can use a range of organic materials to boost fertility, such as homemade garden compost and various farmyard manures. Composts and manures vary in their pH and their nutrient content.
Fresh animal manure has much of its NPK (nitrogen, phosphorus, potassium) content in readily available form, so great care should be taken if it is used on the plot. The abundance of nutrients in a fresh manure can cause more harm than good, as the high nutrient levels can depress the activity of microorganisms, and the soluble nitrogen is readily leached from the soil and may even pollute nearby watercourses. It is far better to use a well-rotted manure, which will help to build up soil fertility over a long period of time, but will not feed the plants directly. The description ‘well-rotted’ indicates that it has been allowed to age and break down, and can be safely added to soil.
Composts are made from a mix of organic materials. They have been stabilized (broken down into new compounds that may be harder to decompose, and some of these become bound to the soil particles), so there is more dry matter. The percentages of NPK in readily available form are much lower, so there is much less risk of nitrogen leaching. Composts tend to be a good source of potassium and phosphorus, providing a longer-term supply of nutrients. They are bulky, so are usually added as a mulch, or dug in as a long-term soil improver.
This new raised bed has been filled with well-rotted horse manure.
The composting process
Composting is the breakdown of organic materials by microorganisms, and is an essential part of the biological cycle of growth and decay. It is readily visible in natural habitats – look at a woodland floor and you will see a layer of leaf litter. It doesn’t stay there long, because the bacteria, fungi and other microorganisms break down the complex organic compounds such as proteins into simpler inorganic ones such as nitrates and phosphates, which plants can use. The end product of decomposition is humus: a brown, crumbly, organic material rich in nutrients and soil life.
There are three phases to composting. The first stage is when the materials start to break down as a result of the activity of the microorganisms, especially bacteria. This process generates heat. The temperature rises steadily and after a few days will exceed 50°C (122°F). This temperature kills off the first-stage microorganisms, and they are replaced by others that can tolerate higher temperatures. To kill off pathogen organisms in the compost you need to achieve at least 55°C (131°F), but if it rises above 65°C (149°F), beneficial organisms will be killed too, so the compost has to be turned and aerated, lowering the temperature. This mixing also helps to incorporate more oxygen, keeping all the breakdown processes aerobic. This high-temperature stage can last for days, weeks and in some cases months. The final stage is when the activity of the microorganisms declines as the supply of high-energy compounds has been exhausted. The temperature falls and the first set of microorganisms takes over again, and other organisms arrive in the mix, such as woodlice and tiger worms.
The microorganisms involved in composting include bacteria of many different types, each adapted to working at a different temperature. They release enzymes that digest many substances, in particular the nitrogen-rich foods. The fungi and actinomycetes (a type of bacteria) are capable of breaking down tough woody materials. The actinomycetes are related to fungi, and they give soil its characteristic earthy smell. Fungi and actinomycetes are particularly important in the final stages of composting, when all that is left is the tough woody material rich in lignin and cellulose, and they help to form the humus.
No smells!
It is important during composting to make sure there is plenty of oxygen for the beneficial microorganisms to function. As soon as the oxygen levels fall or there are pockets that lack oxygen, the process of decomposition slows down. When there are anaerobic (oxygen-free) conditions, other microorganisms take over. They work more slowly than the aerobic ones, do not generate much heat, and their by-products are smelly gases. If your compost heap is turning into a putrid, smelly mess, you have anaerobic microorganisms at work.
These fallen leaves will soon be decomposed by bacteria and fungi.
Carbon and nitrogen
When people talk about compost, they often discuss the importance of the carbon-to-nitrogen ratio (C:N) and how it affects the breakdown process. Carbon makes up much of a plant’s support structures – the cellulose in the cell walls and the lignin in the woody parts – while nitrogen is an essential component of prot
eins, which are found in all cells. Cardboard, paper and woodchip all have a high C:N, of around 400:1, because they are made from woody fibres, while animal manure, grass clippings and other lush green plant material is rich in nitrogen, with a C:N of 25:1 or less. The optimum C:N for creating a sweet-smelling, fertile compost is 25-30:1, but this ratio doesn’t exist in many plant materials, so they have to be mixed – ‘green’ (high in nitrogen) with ‘brown’ (high in carbon). If there is too much carbon, decomposition will be slow, but if there is too much nitrogen, as in a pile of grass clippings, decomposition will be rapid and you get left with a smelly, slimy mush.
Dead leaves are high in carbon and, in the absence of other materials, break down very slowly. The resulting leafmould is low in nutrients but is a valuable soil improver.
The balance of C:N is critical to soil life too. Compost with a lot of visible (undecomposed) woody material has a high carbon content, and when you spread this compost on soil it can create problems. To break down the carbon, the microorganisms use the nitrogen in the soil, depriving the plants (this is known as ‘nitrogen robbery’). To stop this happening, you need to make sure that the materials you add have a good balance of carbon to nitrogen – a C:N of about 25-30:1. If you have compost with a lot of undecomposed woody pieces, you should add it to the soil in autumn, to give the microorganisms all winter to finish the decomposition and to allow time for the nitrogen levels in the soil to build up again.
A classic row of compost bins in Perth, Australia.
Making compost
Composting is an absolutely essential element of a productive small plot, allowing you to recycle all the organic matter, so you can return nutrients to the soil for the next crop of plants. Whole books have been written on the composting process and everybody has their preferred way, so here I will just touch on the basics of making a good compost.
Composting takes time. Many of us, I suspect, have a compost heap in the corner of the vegetable garden where we toss the weeds and grass clippings and let nature take its course. That will work . . . it’s just that it will take time and often creates a compost that is full of weed seeds and pieces of twigs and tougher materials. Alternatively, the process can be completed in 6 months or less by using the right mix of materials and turning it several times.
On my plot I have a number of compost heaps. In my raised-bed area, I simply designate a bed as a compost heap and pile up the materials as I weed, trying to have a mix of about a third to a half ‘green’ and up to two-thirds ‘brown’, adding shredded paper, cardboard or straw as needed to balance the ratio. The green material will break down quickly, uses up oxygen and generates some heat, which will fuel the decomposition process. I cover it up with black plastic and each week add fresh material from my weeding and pruning. By the end of the growing season I have a good-sized heap, which I leave over winter and use the next year for the hungry crops such as potatoes. In this system, the temperatures may not rise high enough to kill the weed seeds, so there will be a good flush of weeds, which I hoe off as they germinate.
In addition, I have a traditional row of compost bins made from recycled pallets, which I fill in much the same way as on the raised bed. The slats allow air into the compost – an essential element for composting, as it keeps the process aerobic, and I don’t keep them covered all the time, so water can reach the heap too (it shouldn’t be too dry but not too wet either!).
A compost bin made from pallets has plenty of gaps to aerate the heap as it builds up. The slats across the front have been removed while the bin is filled.
By carefully controlling the mix of composting materials, you can produce a compost that is either rich in bacteria or rich in fungi, which can be put to different uses. A bacteria-rich compost is one that has had more nitrogen-rich materials present, such as legumes, grass clippings and manure. These are rich in protein and sugars, which fuel the growth of bacteria. The resulting compost is good for mulching soils to grow vegetables (especially brassicas), flowers and herbs. It’s also the preferred compost for making compost teas (see page 55).
A compost that is rich in woody material has a high fungal component, and is good for mulching fruit trees and bushes, new hedgerows and other perennial plants.
Compost colour
Colour tells you a lot about the quality of a compost. The final compost should be dark brown: aim for the colour of a 70%-cocoa chocolate! If it gets too hot, the compost will be very dark brown, almost black, indicating that anaerobic conditions were experienced, so the compost will lack nutrients and microorganisms. A white, ashy layer indicates that there was compaction in the compost heap, which can be caused by having too much fine material.
Materials that can be used for composting
‘Brown’ materials (high in carbon – C:N 50-600:1)
Bracken
(C:N of 50:1) Can be readily obtained in some areas.
Cardboard, newspaper and shredded paper
(C:N of 350+:1) These should be torn or shredded to create a larger surface area for the microbes to work on, and dampened. Avoid finished glossy papers, which don’t rot down easily. Sheets of cardboard and newspaper can also be used as a weed barrier at the bottom of a new no-dig bed, dampened and covered with other mulching materials.
Dead leaves
(C:N of 40-80:1) Readily available from many gardens.
Straw
(C:N of 50-150:1) Straw is dried stems, with little sugar content. You may be able to get spoiled bales of straw for free locally.
Wood shavings, woodchip, sawdust
(highest C:N, of 300-600:1) Your local timber yard or tree surgeon may be able to provide these for free, but avoid treated wood and yew. Wood chippings are also great for mulches and on hugelkultur beds (see page 54).
Woody garden waste
(C:N of 50-400:1) Shred your woody garden waste, as smaller pieces will break down more quickly.
‘Green’ materials (high in nitrogen – C:N 5-25:1)
Animal manure
(C:N of 5-20:1) Animal manure has a high nitrogen content. You can use poultry manure from your chicken houses or buy manure in from local farms or stables.
Coffee grounds and teabags
(C:N of 20:1) Easily obtained and often available from coffee shops.
Comfrey leaves
(C:N of 10:1) The leaves of this excellent plant can be cut and used as a mulch, added to the compost heap or rotted in water to make a foliar feed. See page 57 for more details.
Grass clippings
(C:N of 9-25:1) A readily available green material. Be careful not to add too thick a layer of clippings, as they can rot down to create a dense, impenetrable mat. Ideally, mix with shredded paper or newspaper, or cardboard.
Green garden waste
(C:N of 5-25:1) Weeds and prunings from the garden.
Hay
(C:N of 15-25:1) Hay is rich in sugar, which is good for feeding bacteria in the heap. Dampen to activate this process. On the downside, hay is likely to contain seeds, which will germinate, and if used as a mulch it can encourage slugs and snails.
Seaweed
(C:N of 5-25:1) This is high in nutrients and makes an excellent mulch as well as compost activator. If you live near or have easy access to the coast, you may be able to harvest seaweed from the shore for free, especially after a storm, but check that there are no local laws restricting its collection.
Other materials Other ‘green’ materials include old cut flowers, vegetable and fruit waste, citrus fruit skins, pondweed, spent hops, wool (fleece from shearing), shredded silk clothing – and urine!
Do not add the following materials to your compost heap:
Diseased plants; persistent weeds (such as bindweed and ground elder, which regrow from tiny pieces); soot and coal ash; dog or cat faeces and cat litter; glossy paper; meat, fish, fat and cooked foods (which smell and attract vermin); grass clippings from lawns treated with weedkiller.
Sometimes, your compost heap needs a littl
e help. You may have a lot of brown material and not enough green, or the weather may be cool and the microbiological activity low. In these circumstances you can use activators – substances that are high in nitrogen – to kick-start the whole process. Activators include blood-meal, bonemeal, comfrey tea (see page 57), fresh animal manure, seaweed and urine.
Hugelkultur beds
Hugelkultur (hoo-gul-culture) beds have been used for hundreds of years in Eastern Europe. They are heaped or mound beds – neither raised beds nor compost heaps, but something in between – and make use of woody waste, that is fallen branches and logs. They are great for long-term fertility, moisture retention and increasing the surface area available for planting. As they contain a lot of rotting wood, there is a supply of nutrients for crop plants for 10 to 20 years, plus the decomposition generates heat, which gives the beds an early start in spring. There is excellent aeration from the plentiful air spaces between the logs and branches, while water is retained rather like in a sponge. This means that there is little need to water the bed in all but the driest summers.
These beds are built by first digging out a trench about 30cm (12") deep, which is filled with logs and thick branches. These are covered by smaller branches and woodchip, then topped with compost or well-rotted manure. Some people prefer to make steep sides to the beds so that compaction is avoided; others prefer a more shallow bed. It’s all a matter of preference. Since the logs and branches are carbon-rich materials, they take up nitrogen as they decompose, so it’s important to have a thick layer of nitrogen-rich compost and initially to grow nitrogen-fixing plants such as legumes. Once the wood starts to decay, nitrogen is released. To kick-start the decomposition process, some people add green matter, leafmould or seaweed around the logs.
