Composting: How it works and why you need to make it?

I hate taking instructions with no explanation. 2×2 is 4? But why. Add in baking powder to make your cake rise…how does that work? Mix cardboard and grass cuttings in this ratio and get compost – but why that ratio, what’s breaking them down? How can I make it go quicker?

I find that if I can understand how – then I am more likely to remember to do a thing. But, if you just give me a list of requirements or ingredients I am less likely to remember.

But, if you tell me that my compost bacteria need grass to reproduce and cardboard to eat along with lashings of oxygen, then I’m more likely to remember to put in a mix of materials and aerate my compost pile.

I can visualize the process and the process becomes second nature.

I confess, I am not the world’s expert of compost. My first successful batch of cold compost was done with no real knowledge, and just a slight chop and cram into a council supplied bin. 1 year later (mainly because I’d forgotten about it), I was overjoyed to discover it had turned into rich, DARK, compost.

It was one of the most exciting things I have ever seen. Over the next few days, I kept on going back to the pile to run my fingers through it. I was desperate to tell everyone about it – but who else would be excited about black compost. My brother loves to garden, but he was pretty ‘meh’ about it. My husband, who prefers hobbies with batteries or a plug, looked bemused.

But inside, every time I thought about it, my heart skipped a beat. Is that mad!!!! How can decomposed black fluff make one so happy. I think it was a combination of joy that it had worked, amazement that nature is so clever, and wonder in how on earth it had happened. Oh and the ‘free’ element of it added a layer of sparkle too.

What is composting?

Composting is the biodegradation of organic matter and carbon material, by microorganisms. Carbon, nitrogen are broken down using oxygen and water to create compost.

Compost has been used to support soil food web organisms long before anyone knew they existed. It is a proven, effective growing medium. Compost can inoculate an area with microbes to support a soil food web

Jeff Lowenfels and Wayne Lewis: “Teaming with Microbes,” p124

How is all this material broken down?

Macro-organisms like ants, beetles, centipedes, worms, flies, millipedes, slugs, snails, spiders and woodlice are all munching through your compost.

Then you have smaller organisms like nematods, mites and protozoa that eat some of the organic waste and the bacteria growing on it.

Below them are the teeny tiny microorganisms. These are actinomycetes, bacteria and fungi. What species of bacteria and fungi you have in your compost bin will depend on the temperature and the type of organic matter you have added. In 1 teaspoon of compost, you may have 1 billion bacteria.

Why does my compost get hot?

All those micro-organisms doing their thing makes it hot. Converting all that organic matter and carbon takes energy and that creates heat.

As the temperature rises, different types of bacteria and fungi come to dominate. It’s like a micro-game of thrones.

If things are cold, say <15°C, then most of your microorganisms are going to be sleeping. You’ll get a few psyochophiles in there though. These are organisms that like things cold. You can find them in bottom of the sea or in the Siberian permafrost. They are also know as extremophiles. The extreme junkies of the the micro world.

Once things start getting hotter to >20°C, then another set of bacteria are taking over. These are the mesophiles. They like a nice ‘summer’ heat up to 32°C. They can break up your easy to digest organics. If you are using a cold compost, then you are likely to have these little buddies as permanent residents.

Once things get ‘heat-wavy’ and more ‘oveny,’ then the thermophiles take over. These are the super-decomposers, tearing up cellulose, proteins, fats and turning it into humus. They will keep things hot for a few days until they run out of things to eat. Turning the heap can help bring the cooler organic matter from the edges into the middle and give them a boost. At 60°C all those weed seeds, and yucky pathogens and parasites will be obliterated.

As the temperature drops the mesophiles wake up to cure the material make things look a bit more composty. Fungi will help break down the harder woody materials (lignin) and tough shiny leaves. Fungi operate at cooler temperatures, so if your bin gets above 50°C you are not likely to have that many fungi left. A cold compost would be better if you want a fungal compost for your perennials, shurbs and trees. Basidiomyces sp fungi are the ones responsible for decomposing tough woody things. Aspergillus fumigatus will be able to survive a hot composter.

In this stage the bacteria and fungi are releasing nutrients into the compost and your bigger organisms like worms and woodlice are also helping now.

What container do I need to keep my compost in?

You don’t actually need anything. You can just make a lovely big heap of carbon and nitrogen materials.

You can buy one of those fancy compost makers, but people tend to pile stuff in them and ignore it. Six months later, when they’re planting vegetabls and want some nice fresh compost, they find the contents are either dry or wet and stinky. Bins make it unlikely you’ll ever turn your compost. Compost needs love, not a container.

Stephanie Rose, Garden Alchemy, p113

But it make it easier to turn if you have some sides, but these can be made with a pallet. Alternatively, you could buy a plastic or wooden compost bin, that has an open bottom. This enables those macroorganisms to come in and out.

What ingredients do I need to make compost?

You need nitrogen, carbon, oxygen and water.

Nitrogen is also referred to as – greens – because its mainly the green stuff that will have all the nitrogen in it. So these are materials like grass clippings, garden clippings, animal manure, hair, seaweed, green leaves, egg shells, feathers, coffee grounds, vegetable and fruit peels.

Carbon is found in ‘brown’ materials, like shredded paper, cardboard, dried leaves, hay, sawdust, wood chips, newspaper, egg cartons, toilet paper rolls, and wood ash.

If you are using a special hot bin compost, then its special insullation will help your bin heat up to over 40°C. This will ‘cook’ any cooked food waste, bones, fish and even meat.

Don’t compost pet poo, diseased plant material, coal ash, dairy, and any organic material treated with chemicals.

Water is very important. You want all your materials to be moise – a bit link a damp sponge.

What quantity of browns and greens do I need in my compost?

This is where it get’s tricky. If you can get the right balance of carbon, nitrogen, water an oxygen you will have a lovely hot compost that finishes very quickly.

If not, you will still get compost, but it will take longer and might smell if there is too much nitrogen, or do nothing if there is too much carbon.

You want to aim for 25% nitrogen sources and 75% carbon.

Unfortunately not all carbon and nitrogen is made equal. A bucket of grass cuttings

Why is oxygen and turning my compost important?

To survive, the bacteria need carbon (from your brown materials) and nitrogen (from the greens). You want aerobic bacteria – ones that use oxygen, and not stinky anerobic bacteria. Aerobic bacteria produce masses of heat as they ‘eat’ the carbon. The nitrogen helps the bacteria to multiply.

Without oxygen all this lovely bacterial frenzy will slow down. It’s the reason why you should aerate and ‘turn’ your compost heaps or bins, to ensure there is enough oxygen for those bateria to do their thing.

How do I make fungally dominated compost?

Perennials, shrubs and trees – any plants that are in the ground for a long time, prefer soil that is fungally dominated. You can also make fungally dominated compost by adding more brown materials like dry leaves, twigs and cardboard. These all contain cellulose, lignin and tannin that the fungi can digest. You will need a cooler compost for this too.

Chemical fertilizers provide plants with nitrogen, but most do so in the form of nitrates (NO3)…plants that prefer fungally dominated soils ultimately won’t flourish on a diet of nitrates.

Teaming with Microbes, p25
Graphic showing ratios needed for fungally dominated compost

Jeff Lowenfels’ recipe for a fungally dominated compost is:

  • 5-10% alfalfa meal (You can either buy pure alfalfa or a meal that is usually fed to horses, and is alfalfa mixed with molasses. Alfalfa is packed full of carbs and proteins which is great for soil microbes)
  • 45-50% grass cuttings
  • 40-50% brown leaves or wood chips

How do I make bacterially dominated compost?

 Graphic showing ratios needed for bacterially dominated compost

Annuals and grasses prefer a bacterially dominated soil. To make a bacterially dominated compost, however, you just add more nitrogen.

Jeff Lowenfels‘ recipe for a bacterially dominated compost is:

  • 25% alfalfa meal
  • 50% grass cuttings
  • 25% brown leaves or wood chips

You could amend the ingredients slightly as long as you keep to those ratios. You could swap out alfalfa meal for other accelerators and a bit of garden soil.

I’ve been looking for a perfect compost recipe…but even though I try to stick to them, realistically, whatever gets pruned goes in the compost. I just try and make sure that once I have a bucket of green filled – I balance it with the right amount of brown. I used to stress about it, but now after a few years of composting, even if things go wrong, at least I now know how to fix it. Too dry, add water. Too stinky, add browns, not enough heat, add greens.

How long does composting take?

With a compost bin or heap where you just pile material on and do nothing with it, then it will take up to a year to turn into lovely black and crumbly compost.

If you have a hot bin, then it can take as little as a month.

How do I speed up my compost?

  • Chop up your ingredients into small pieces. If you want things to be fast you need to increase the heat. To do this you need all your compost ingredients to be small. This increases the surface area for the microbes to attach to and do their work. Aim for pieces no bigger than 2 inches. Anything smaller than 1 inch will clump together and make your compost pile sludgy.
  • Give it air. You also need to ensure oxygen gets into your compost pile. That means getting a big garden fork and turning your compost pile every day.
  • Add a compost accelerator. You can actually buy bacteria and fungi that you can add to your compost, but you can also add your own compost accelerating plants. Maye E. Bruce discovered these acclerating plants to create ‘Quick Return’ (QR) compost in 1935. In her compost recipe, she used Chamomile, Dandelion (Taraxacum oficinale), Oak Bark, Yarrow, Valerian and Stinging Nettle (Urtica dioica). She dried all her herbs and then added the powder and honey to a watering can before adding it to the compost pile. According to Stephanie Rose in her book Garden Alchemy, you can also use Black Elderberry (Sambucus nigra), Calendula ( Calendula oficinalis). Also tap root accumulating plants like, Comfrey (Symphytum officinale), Hollyhock (Althea rosea) . If you don’t have time to dry, then just chop them up and add to the pile. I regularly add borage, nettles and comfrey to my compost mis.
  • Add soil. If you add some garden or woodland soil in, then you will be adding in some extra bacteria and fungi too.
  • Get things super-hot. If you are using a hot composter then your bin will probably reach up to 60°C. As long as you ensure there is plenty of air flowering and enough brown materials to keep the temperature up, then you could have compost within a few months.
  • Turn, turn and turn again. By turning you are going to keep the heat up and add more oxygen. This is a good chance to check if the pile is too wet or too dry as wll.

How do I know when it’s ready?

It will smell earthy. Feel crumbly. And be dark and rich in colour. You should be able to discern any recognisable elements, except small twigs.

Why is it smelly?

If it starts to smell that’s because your compost pile is too wet and doesn’t have enough air. So the anerobic bacteria have taken over and they are producing the putrid smells.

Add some more brown materials, and keep turning daily until you get back to a nice harmonious balance.

If all else fails….leave your pile for a year, and you will still be rewarded with the black stuff!!!

If you get it right – I promise, you’ll be dancing on your compost heap – just like Bob (I love Bob). Check out this happy place song.

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