Composting

Decomposition, the breakdown of once living organic matter into elements that are re-used by plants for growth and reproduction, occurs all the time naturally in the environment around us. Leaves fall from deciduous tress in the autumn and, when not removed by us, have largely disappeared by the summer. The following autumn the cycle repeats itself. Decomposition or composting, (the tidier process we gardeners use to recycle waste from our gardens), must be easy! However I see many unsuccessful attempts at composting.

The mistakes

If given enough time all dead organic matter eventually decomposes, so in that sense there are no mistakes. The biggest mistake I see people making is throwing everything from grass clippings, weeds, long woody branches etc without direction or planning into their allocated compost heap, bin etc,  resulting in an unstructured tangled mess. The material all too often compacts, drys out and results in very slow decomposing material which is difficult to work.

Amateur science

Most of us have a rough idea about how decomposition works; (worms eating leaves etc.) The decomposition process is on a scientific level much more complicated than that. However with a little insight, understanding and appreciation we gardeners can become knowledgeable, expert composters. If you really want to know how to become successful at composting bear with me on the following paragraphs, it will make sense and help you on your journey to become an expert at  composting and impart your knowledge onto others.

Microbe Biodiversity

Invisible to the naked eye healthy garden soil is teaming with a diverse microbial life. Although estimates vary, scientists calculate that there are around 500 million to one billion microbes in a teaspoon of soil comprising many thousands of different species. The microbes are made up of single celled bacteria, archaea (similar in appearance but with a different metabolic pathway to bacteria), nematodes, fungi, yeasts (single celled fungi), protozoa (eg amoeba). They interact  dynamically with one another as predators, prey and parasites within the soil particulate matter, breaking down existing organic matter during their complex interactions into forms plants can use.

Recent advances in microscopy has established that microbes, particularly  bacteria also exist not only on the surface but within all parts of plants; the roots, stems, leaves, flowers. These endophytic (living inside plants) microbes are involved with what we see as the final stages of decomposing organic matter. The result being water soluble nutrients being made available in a form for plants to use for growth, flowering etc. Recent research also suggests  that it is the plants that choose and determine microbial actions rather than the other way round. Scientists think plants need to be fussy which intracellular microbes they allow into their vulnerable cell cytoplasm. The wrong microbe could cause disease and result in death of the plant. For a bit more insight on one interaction click here for Rhizophagy. 

It is also known that most plants have evolutionary associations with mycorrhizal fungi which produce a network of mycelium increasing access to otherwise unavailable nutrients. The hyphae that make up the mycelium are extracellular growing between the plants cells rather than in the plant cells. This symbiotic relationship provides the plants with with nutrients and moisture whilst the fungi obtains organic compounds including carbohydrates and lipids for the production of energy, cell production and insulation. The discovery of plant/microbe associations and is still in its infancy and scientists are just beginning to understand this extremely complex evolutionary relationship. 

Quick composting side note

Just to remind the reader this is all relevant to composting learning advice. These huge numbers of diverse microbes require a film of water to complete their life cycles from mobility, feeding to reproduction. Keeping the compost heap moist, (not soaked) increases microbial activity and in turn speed’s composting. Aerobic bacteria (requiring oxygen for respiration) are faster at decomposing organic matter than anaerobic bacteria , so turning the heap to allow air in is helpful. If the compost heap is allowed to dry out during the growing season and in the colder winter period when temperatures are lower these decomposing microbes become largely inactive, entering into a state of dormancy.

Another side note (the Geek in me)

Many scientists note that plants and microbes etc do not become fully dormant. During periods of cold to extreme cold in temperate climates they have evolved strategies to cope with the temperatures. They can produce anti freeze chemicals to make their cell membranes more flexible to freezing. Plants have been observed moving water from inside their cells to the outside and sealing off parts of their tissue like the xylem. Air bubbles can be created in conductive tissue  which eases the pressure of expanding frozen cells on the overall structures of the plant. At a microscopic level where plants structures are not seen as smooth structures as observed by the naked eye films of unfrozen water contains active microbes have been observed.

Invertebrate Biodiversity

The decomposers we are more familiar with are the invertebrates; animals that lack a backbone. They can be classified as 6 legged insects, 8 legged arachnids such as spiders.  Millipedes and centipedes which belong to the class myriapods. Springtails and bristletails to the class Collembola. Worms and leeches belong to the annelids.Woodlice are actually Crustaceans (aquatic arthropods).

A  healthy habitat from soil to the vegetation it supports contains a diverse community of invertebrates interacting similarly to the microbes. A proportion are directly involved in decomposition such as woodlice aiding microbes by feeding on and reducing decaying organic matter to carnivores such as spiders feeding on the woodlice which in turn are returned to the soil through faeces. The complexity of these associations goes deeper as all these invertebrates contain microbes within their bodies and externally just like we have microbes living on our skin and in our guts etc. Biodiversity is truly complex and possibly impossible to completely understand and work out.

The diverse invertebrate community occupies numerous complex interacting niches which is interesting to briefly consider.  Larger in size than microbes they are easier to observe and translate their interactions as similar to what is going on in the microbial world. It is also interesting to note that the invertebrate communities  and possibly microbe communities in our temperate UK gardens are not as rich as those found in tropical countries although in the UK we have biodiversity rich temperate rainforests. Only 1% of the world’s landmass is temperate rainforest so we in the UK can boast a rarer biome than tropical rainforests which sits at around 8% of the worlds landmass.

Invertebrates such as woodlice feed exclusively on decaying plant material, slugs and snails eat  both decaying and living green plant material. Others invertebrates feed on fresh juicy sap found in fresh young growth; contributing to decomposition through faeces produced. Examples include aphids, thrips, green shield bugs. Remember  all these invertebrates have decomposing bacterial associations. 

Other invertebrates extend their palette of decaying plant matter to include decaying animal matter. these invertebrates include millipedes, mites and ticks. Earwigs eat fresh green plant material but also small invertebrates. Dependent on species beetles feed on both plant and animal material.

Earthworms eat soil, digesting it’s organic material and releasing excreted matter, seen as worm casts. Other worms and leeches feed on decaying leaf matter.

Carnivorous invertebrates contribute indirectly by their faeces. Spiders, centipedes, damselflies (adult & larvae) dragon flies all feed on the invertebrates. Dragonflies have been recorded feeding on small fish and tadpoles.

Different stages of an invertebrates life cycle can  feed on different foods,  lace wing larvae feeding on nectar, pollen and honeydew whilst in adult form feeds on aphids.

The minute wingless springtails and bristletails ancestors of todays winged insects feed on decaying plant and fungi. 

Ants will feed on plant material as well as other insects invertebrates

The caterpillars of butterflies feed on decaying but mainly living plant material much to the annoyance of gardeners, however the attractive adults contribute to plant pollination when feeding on nectar. Moth caterpillars feed on plant material from leaves stems flowers and roots. Many adult forms have no mouths but some species can drink nectar and other plant sap.

Adult wasps feed on nectar,  ripe fruit and other insects, larval forms feed on aphids and other invertebrates. Bees feed on nectar and are main valued pollinator. 

As can be seen from the brief summary of the complex interactions occurring in the invertebrate world the invisible (to our eyes) microbe world is equally if not more complex. Todays complex diversity has evolved over billions of years as part of a stable ecosystem able to sustain life.  During their living interactions and ultimately in death all invertebrates and microbes themselves contribute to decomposition and in turn recycling and the circle of life.

By understanding and respecting the importance of the unseen and unnoticed micro world going on around and beneath us we realise the importance of a lighter physical approach to gardening , using less, often unnecessary bought in synthetic products such as fertilisers and weed killers and the value of supporting recycling. To be truly eco-friendly in our garden practices composting is essential, practices and space must be allocated for this to happen . What lives, grows and dies in the garden stays in the garden. 

Another composting side note

The addition of fertilisers, weedkillers and other products to the soil can unbalance and drastically reduce the numbers of microbes which through their intact numbers and interactions result in a poor soil with weakened plant growth. There are billions of microbes in every handful of soil and compost, if left to their own devices will provide sufficient nutrients for healthy plant growth. Individual microbes through time die and decompose themselves contributing to plant growth 

Composting Practices & Space

We now have an understanding and appreciation of the presence and value of microbes and invertebrates in decomposition and in turn their importance in composting. An area allocated to composting in our gardens should have the same importance as allocating a space in our homes for cooking or sleeping. The space should be an integral component of our garden design rather than a tucked away necessity in a corner.  

The space should ideally have some contact with the soil and good easy access for removal of compost. Handy access to a nearby outside tap and hose for ease of keeping heaps from drying out is also preferable. Depending on the size of your garden compost heaps can comprise the common round green compost bin style, wooden structures , loose heaps or a mixture of all. In my garden I have built large wooden area, split into three sections with completely removable fronts for ease of access. One section I use as a holding section for large volumes of newly cut material.. The other two sections use as my main composting heaps. Layering green and browns and every few weeks aerating the heap by transferring the entire pile into the adjacent section. This also gives me an opportunity to moisten dry bits with my hose.

Successful speedy composting relies on a good mix of green and brown waste.What is this? Scientists have identified that the best ratio for decomposition is around 30% carbon to 1% nitrogen. Carbon (browns) and nitrogen (greens) are the two most important elements for microbial decomposition to occur. Carbon supplies the energy to make the building blocks of 50% of the mass of microbial cells, whilst nitrogen is the most important component of proteins, nucleic and amino acids and enzymes for microbial cell growth and function. A lower ratio of carbon results in an excess of nitrogen released as foul smelling ammonia gas, where as,  too much carbon results in decreased microbial populations.which in turn results in cool, slow decomposition.

It is important to note that scientists measure this ratio as dry weight and not bulk weight so a small amount of damp green grass clippings is sufficient to speed the decomposition of a large drier mass of material high in carbon such as brown leaves or shredded stems. Green (high nitrogen) matter is considered as grass clippings, green plant cuttings, fruit, vegetable scraps and coffee grounds. Whereas brown (high carbon) matter is described as brown leaves, wood chip, cardboard etc. 

In reality a lot of garden waste material comprises decent quantities of both carbon and nitrogen such as woody evergreen prunings Other elements such as phosphorous, potassium, iron, calcium etc are considered to be present in sufficient quantities in all garden derived materials. Although there are scientific published tables on the internet on C/N ratios in the garden setting a rough calculation is sufficient and keeping the 30:1 ratio in mind together with regular turning and ensuring the heap does not dry out learned experience will develop quickly.

Having this balance of material in the compost heap will aid and in turn speed decomposition because the microbial community will be sufficiently diverse with bacteria breaking down green matter and fungi the cellulose and lignin of brown matter. Most microbes prefer aerobic conditions so turning the compost heap will add oxygen and in turn speed decomposition. Keeping material to be composted as small as possible helps speed decomposition and an easy to work medium.

Composting in my Garden

Winter standing vegetation being cut back

In my own garden I allow vegetation to stand over the winter providing aesthetic winter structure but more vitally a habitat for over wintering stages of insect species, ground level basal crown protection of plants during periods of frozen ground as well as in situ decomposition of organic matter. I do not cut back the skeletal remains of herbaceous plants or prune shrubs till spring bulbs start showing the first signs of emerging from the soil, normally coinciding with increasing day light hours and some soil warming. 

Domestic garden shredders although comparatively cheap have narrow input hoppers making the shredding process slow and are limited in what they can chop up successfully.  There are heavier duty domestic and professional chippers/mulchers available but they can be expensive and although excellent at chopping woody material are not very efficient at shredding herbaceous material. 

I cut down my own herbaceous perennials quite close to ground level during a dry spell allowing me to pass significant quantities of woodier straight (ish) material through a domestic (not great) garden shredder. I will also use secateurs and loppers to chop up pieces into bits ideally no more than 3 three inches (8cm) long. The smaller you can cut your material the faster it will decompose and the easier turning and working the compost will be.

Vegetation cut back awaiting partially decomposed mulch from compost area

Because I have a lot of herbaceous perennials throughout my mixed borders  I cut down vegetation close to ground level bringing my secateurs and hedge cutter  into play. I place the long cuttings into small bundles. These I chop up into small pieces using my hedge cutter in a back and forth motion along the length of the small bundles.

Hedges and some shrubs allow me to use the  hedge cutter passing the reciprocating blade forward and back wards motion over the stems in a gradual decline resulting in lots of small pieces. I call this "the Disney cut’’ because on visits to Disney World, Florida with my children I  noticed that no matter what time of year you visit  their hedges and shrubs always look neatly trimmed for the park visitors. They use a little but often method of pruning shrubs allowing much of the clippings to remain on the ground acting as a feed as well as weed suppressant mulch. In the same vein some of the clipped material can be left in situ whilst the easy to remove bits can be bagged with the rest of the prunings. 

In my garden I place the material into a large wooden holding frame. One ton bulk bags also work for this. Garden tend to have an excess of green, (high nitrogen) matter especially leaves during the growing season. As winter approaches and daylight and temperatures reduce  leaves stop making food and their chlorophyll, is broken down. Resulting in normally muted pigments including oranges and reds becoming more prominent until leaf fall and bare standing woody stem. The brown leaves and woodier stems decompose slower because of the remaining cellulose and lignin. This type of decaying organic matter tends to be dominant in the garden in winter and can take longer to decompose.

Bulk bags holding winter prunings. This predominantly high carbon material will gradually be layered as 30:1 dry weight with grass clippings in spring/early summer to main composting section.

As grass begins to grow in spring,  the high nitrogen clippings from grass areas that I keep short such as paths and play areas every two weeks or so are  layered into my main compost heap and cover with a layer of high carbon brown material from earlier pruning operations and now residing in  my holding bay.  Remember the 3:1 ratio  dry weight. 

Every four to six weeks or when the mood takes me I turn all the material into the free adjacent bay and if dry damp the material down with my hose. This helps aerate the compost and speeds decomposition. Because the material is small it is relatively easy and quick to transfer from one bay to another. It is actually quite fun to see how decomposition is going. This allows the centre of the heap to heat up through aerobic microbial action and speeds decomposition. Noticeable also is that invertebrates do not occupy the hot centre of heaps but are found nearer the cooler  surface and edges of the heap. 

Remember mixing green and browns together with sufficient existing moisture and aeration maximises the  diversity and quantity of the microbial community and in turn speed decomposition into a wonderful soil conditioning medium which when applied to the surface of the soil provides a healthy soil for our plants. Our plants will repay us visually with vibrant displays.

The following spring when the main cutting season starts again the cycle is repeated and once again I temporarily transfer my chopped prunings to my bulk bag(s) and holding bay. Most of the compost in the other bay is ready to apply as a 1-2 inch mulch over  mixed border beds around the ephemeral emerging bulbs and herbaceous perennials starting to show signs of growth. The compost does not have to be a fully decomposed sweet smelling material as suggests in much literature. It is partially decomposed and will continue to decompose further in situ providing valuable microbes for plants, enhancing soil structure, suppressing some weed growth etc. The compost lowers down is often fine enough to use as potting compost.

Mixed border cut back in spring with snowdrops emerging towards back of bed which is now covered with microbe dense mulch
Vegetable plots: apply about 1 inch layer in autumn protects soil from winter rains, feeds and protects soil organisms and the ground ready for planting in the spring.

Professional growers of plants and farmers understandably like the quick and easy application of synthetic fertilisers to maximise crop production year upon year. Research now shows that the consequence of synthetic fertiliser application has a negative impact on soil health, reducing inherent soil fertility and structure necessitating the need to re-apply synthetic fertilisers to maintain production levels.  A healthy soil has the microbial life which maintains the structure ( aeration/ drainage / ability to retain nutrients) 

The science behind this long term negative impact on soil health to achieve the desired growth surge of crops in agriculture and ornamental plants in the garden setting is that there is less rhizophagy development  which in turn reduces soil fertility. What is rhizophagy?  

Rhizophagy: Rhizo ("root")  + phagy (" to feed on"). 

It is known that plant roots help anchor and stabilise a plant in the soil and together with root hairs  absorb water and nutrients up through the roots to other parts of the plant structure (stems, leaves, flowers) for growth etc. Root hairs and the mycelial networks of fungal associations are known to increase a plants ability to absorb water and  water soluble nutrients through a more intimate contact with soil particles which would otherwise be unavailable to plant roots.

Water soluble nutrients can be absorbed more effectively with relationships plants  have built up with free living symbiotic microbes in the soil, most commonly bacteria and fungi but also protists. These microbes in this free living phase acquire their nutrients from the soil. 

The root tips of plants are now known to exude a concoction of carbohydrates (a bi-product of photosynthesis) which attracts these free living soil microbes such as bacteria around the root tip  zone. The microbes enter through the root tip and move into the actively growing meristematic cells immediately behind the root tip. These meristematic cells will elongate to form different parts of the plant depending on the needs of the plant in the next part of the root the elongation zone.  

The plant extracts  nutrients from the now termed endophytic ("living inside’’) bacteria by breaking down their cell wall. Exposed nutrients are absorbed and moved  up through the plant for growth.  Although this is fatal to many of the endophytic microbes,  others are cloned, multiply  and released through the plants  root hairs for the cyclic process to continue. The area where the root hairs develop is termed the differentiation zone and is also the point where the initial meristematic cells now have their future roles assigned to them and a}e developing into different parts of the plant stems, leaves etc. Scientist now believe that root hairs evolved to return endophytic bacteria back into the soil as a free living phase for the cycle to continue. Root hairs are single celled extensions forming like a tube for the cell wall.

Garden soil contains enough nutrients for healthy plant growth and by adding organic matter from the garden containing native microbial bacteria and fungi which reproduce  exponentially maximises plant growth. During my 40+ year garden career I have "tidied" many gardens and removed from site large quantities of  dead leaves,  spent vegetation, prunings etc. Many of these gardens have not had any applications of synthetic fertilisers and yet every year there is another surge of growth from enough soil available nutrients. Imagine the luxurious growth potential of a garden healthy soil containing maximum potential biodiversity achieved by making the ‘green bin" largely obsolete.

The native microbes contained within our garden organic matter are already adapted to the micro-climate and soil of our garden maximising decomposition and providing organic compounds  leading to strong, healthy plant growth in a well drained soil. As opposed  to  nutrients from synthetic fertilisers these nutrients are water insoluble and not easily drained away.

This improved soil structure is created by a protein glue called glomalin  which is found in the cell walls of mycorrhizal fungi (its purpose  being to add rigidity and be involved in the transport of water). Any mycorrhizal fungi which die as part of the cycle of life, results in the release of glomalin which binds soil particles together improving soil structure by creating more air spaces for the movement of air and water and in turn root growth. 

This has re-educated me into acknowledging and believing in the benefits and feasibility of the no-dig approach. By keeping digging or forking over the ground to a minimum reduces the disturbance of micro and macro organisms going about their business of ensuring good soil structure is maintained. The recycling of otherwise removed ‘garden waste’ in the form of partially or fully decomposed compost spread over surface of vegetable plots and ornamental beds, mimics natures natural process of returning nutrients to the soil for microbes to texture to the plants for growth. The added benefit being it plays a part in weed suppression.
Perennial weeds can be added to centre of heap to die off in dark and heat, Heat generated quickly and temporarily by fast metabolism of bacteria. Bacteria are also able to break down contaminated material such as herbicides applied to weeds but not lawn weed killers containing. Bacteria used to clean up oil spillls