Sunday, June 28, 2015

Making Compost - part 1

Most food-gardeners would say that making your own compost is an important part of having a successful fruit and vegie garden.  This blog post aims to persuade those who have not made their own compost to give it a go, provide tips and hints on making good compost, and suggest solutions to those who don't have a compost heap because they fear problems with mice and rats.

Why make your own compost?
  • Making compost in your own garden from your own food scraps and garden waste is an efficient way of processing these materials ‘at source’.  It is surprising how many councils still do not collect green waste and turn it into compost. As a society we throw away too much. Your compost heap can help keep your food and garden waste out of council landfill areas.
  • Compost made by you is probably going to be of much better quality than commercially produced compost and it won’t cost you a cent.
  • Good compost is one of the key factors for a successful food garden, so why would you give away to your council the ingredients to make it.
  • There is nothing more satisfying than enriching your garden with ‘your own black gold’.
  • Rather than adding fertilisers directly to your garden where their effect might be too harsh and might damage beneficial organisms in your soil, your can use a compost heap to transform them into substances that can easily be taken up by plants and that will make your beneficial soil organisms thrive.
In order to make compost you need
  • Brown materials – stalks, twigs, dead flower heads, straw, hay. They provide carbon. Ideally this will enable fungi to help in the breaking down process.
  • Green materials – grass clippings, green leaves, weeds, vegetable and fruit waste, coffee grounds. They provide nitrogen that will attract bacteria. Grass clippings will be a great help in heating up your heap. However, do not add them as a dense clump that will be devoid of air.
  • Water – a compost heap should always be damp, but not sodden. A dry heap will simply sit there and not compost. A compost heap or composting bin that is too wet will undergo anaerobic composting, composting without air. It results in a foul-smelling soup that is not good for your soil.
  • Air – the composting method discussed here is aerobic composting, composting using air. Air will initially be trapped when a compost heap is set up. A compost heap needs to be turned from time to time to aerate it and keep the aerobic composting process going. The air needs to be warm enough. In Tasmania do not start a new compost heap in winter.
Setting up a compost heap – in theory
  • Choose a location that is not in full sun (so your heap does not dry out) and do not start a new compost heap in winter as low temperatures may make it hard for the composting process to start.
  • Cut or shred thicker or larger ingredients so they will break down more easily.
  • Do not form layers of your ingredients, but thoroughly mix them with a fork while spraying water from time to time, so the ingredients are damp.
  • You might like to sprinkle some blood and bone while mixing. It will help to get the composting process going and will add good ingredients.
  • This is also a good time to add fertilisers such as seaweed meal, diluted liquid kelp, worm castings, worm juice, seed meal, rock dust and other goodies, if you want to. They will make the result more nutritious.
  • You could also add additives such as clay slurry (see Composting with Clay on this blog) and/or bokashi (pulverized charcoal). Both will aid the composting process.
  • When the heap is ready it would be good to cover it with an old carpet to keep heat in, avoid drying out in hot weather and avoid extensive rains from waterlogging the heap.
The more brown and green materials you have when setting up a heap the better the composting process will work.

Compost for vegie gardens (where bacteria are more important than fungi) is best made with roundabout equal amounts of greens and browns. Add lime if you like your compost to be more dominated by bacteria.

Compost for fruit trees (where fungi are more important than bacteria) is best made with more browns than greens (a 6:4 ratio is good).

In Making Compost - part 2 I will discuss a simple method for determining the approximate brown/green ratio when setting up a heap.

Setting up a compost heap – in reality

With the theory covered, let’s look how in reality most compost is made.

Councils that collect green waste shred everything on arrival at their tip, then with large backhoes mix all ingredients, add water while mixing and then make enormous heaps. Organic farms and people with large properties will do something similar. These heaps heat up quickly to around 65 degrees Celsius, are turned over a number of times and the whole composting process is completed in a number of weeks. This is hot composting. For hot composting the initial heap needs to be at least one cubic metre, preferably bigger. When you open a hot-compost heap it can be so hot, that you don’t want to touch it.

People with small gardens will seldom have enough stuff at one given time to make a brand-new large-enough heap to hot-compost, but that does not mean they can’t make compost. The method used by people with small gardens is cold composting, a somewhat misleading term as a cold-compost heap in action is not cold. It should feel warm when you open it up. Cold-compost heaps don’t become as hot as hot-compost heaps.


In my own suburban garden I have two compost bays next to each other. The photo above shows the content of the right bay ready for use in the garden. New garden waste goes on the heap on the left-hand side and is then covered with old carpet.

Now let’s look at the situation where I have completely emptied the right bay, and the left bay holds so much material that I decide to start a new heap in the empty right-hand bay.

This is how I do my cold-composting:
  • Over 2 or 3 weeks I collect browns and greens in that bay. Every time I have some garden waste I determine whether it will go on the compost heap or into the Clarence Council green waste bin. Why? Because, using the cold compost method, very aggressive weeds (in my garden twitch grass for instance) and very aggressive seeds (in my garden oxalis seeds for instance), thick woody branches, and very diseased garden waste (tomato plants with mildew for instance) may not be 100% composted. Green waste that is fine for my heap I shred or cut into small bits if stringy or bulky, and then for the time being just put them on a pile in the empty composting bay.
  • In the mean time kitchen scraps accumulate in a large outside bin, where they go through the first stage of being broken down.
  • When I feel I have enough stuff to start a small new heap (this is not in mid-winter when it is too cold to start a compost heap) I buy 3 or 4 bags of sheep manure.
  • I now mow the grass area around our hill hoist. This only bit of grass in our garden is there especially so I can add grass clippings to my compost heaps. Grass clippings are full of nitrogen and ideal of starting off the composting process.
  • I add the sheep manure to what will become the new heap. I add the grass clippings, making sure they are dispersed and will not become a dense clump. I add the bin with kitchen scraps. I sprinkle this with a generous helping of blood and bone because this too is ideal for starting off the composting process. Now I mix all ingredients, adding water from time to time, so everything is nice and wet, but not sodden. I finish by putting a strip of old carpet (from the tip shop) over the top to keep warmth and moisture in and sun out and to make sure excessive rain does not drown the heap.
  • In coming weeks I will have more garden waste, that once again I cut or shred if needed. Initially I simply put it on top of the new small heap, just under the piece of carpet.

  • After a few weeks I once again add the content of the kitchen scrap bin and mix all the new ingredients in with what was already there. I might also once again add some blood and bone or complete organic fertiliser (COF – see Complete Organic Fertiliser on this blog) and sprinkle water if the mix is too dry. It may sound funny, but while doing this ‘smell your heap’. If the smell is foul this may indicate inadequate aeration, too much moisture or excessive nitrogen.  By now my trusted workers (worms) will have miraculously found their way from the adjacent compost bay to the new heap, and will be hard at work processing all the yummy ingredients.

  • I simply repeat this process until my heap fills most of this compost bay. Time from starting a new heap to taking away the resulting compost may be four months.
  • When the bay is almost full, and the adjacent bay, that has been sitting there for a number of months, is ready for use in the garden, I empty that bay and repeat the whole process.
There are many variations on this theme. People with chooks may use chicken manure, which is much higher in nitrogen than sheep poo and better at starting the composting process, unless you add too much.

Hot composting compared to cold composting

Hot composting produces 'cleaner' compost than cold composting because the higher temperatures kill seeds and garden pests that may survive in the lower temperatures of a cold-compost heap.

On the other hand, those using the cold-compost method, may add fertilisers and trace elements to their heap that those who have much bigger heaps don’t have time for or don’t want to spend the money on. Worms and other soil organisms will be much more present in cold-compost than in hot-compost, which is a clear advantage. Cold composting takes a lot longer, but the result can be equally or more enriching to your garden. You just need to accept that cold-compost may contain the odd seed and some remnants of twigs and stalks.

If you don’t look too closely, all composts look roughly the same. However, compare compost made from mainly saw dust and pruning clippings to one made from mainly food garden waste and kitchen scraps, and you will see major differences. What comes out depends on what goes in. Commercially produced compost is often fine for general purpose garden beds, but not nutritious enough for vegie-gardens.

Do not add the following things to a cold-compost heap
  • Salt, meat, fish, dairy, fat and cooking oil. Having said this, a Cygnet farmer once told me that there is nothing better than starting a compost heap with a dead possum.
  • Farm manures are fine, but not if the animals have just been wormed. If you buy manures in most cases you won't know.  I have never had problems with sheep poo, maybe because it is more exposed to the weather.  Cat, dog or other pet droppings should also not be added.
  • Clearly diseased garden waste, eg. rose clippings with black spot or tomato leaves with mildew.
  • Any material that you know has been treated with a herbicide or pesticide or weed killer or chemical fertiliser because they may kill the beneficial organisms in your heap.
  • Newspaper and cardboard often contain ink and glue.  Both can be poisonous.
  • Pine needles, pine bark, brown tree leaves, sawdust and woodchips often don’t break down well and are too acid to make compost for vegie gardens.

How to avoid mice, rats and native wildlife

Some areas of Hobart have a rat problem, much more than other suburbs. To me making compost is such an integral part of having a food garden that, if I feared that my compost heap would attract rats,  mice or native wildlife, I would definitely still have a compost heap, but consider the following measures:
  • Construct a compost bay or bays that rodents and others can’t get into by not leaving any gaps between timber planks and using fine mesh to cover your bay(s) completely. Give the compost bay a lid covered with mesh and consider having a floor of mesh as well.  There will be photos of compost bays in part 2 of this series on compost.
  • Do more frequently what you need to do with a compost heap anyway: turn it over and make sure it is damp. This will create an uninviting environment.
  • Don’t put vegetable scraps directly in the compost heap, but store them in an inaccessible outside bin until they have broken down somewhat. Make sure that, once on the compost heap, these scraps are always well-buried.
  • If you live in the suburbs consider getting a cat! Our cat keeps an eye on everything that is going on in my garden and anything that moves at ground level is discouraged from coming back or killed.

Composting is a hot subject

While preparing for the writing of this blog post, I compared the advice by a number of experts on the subject, and guess what? They don’t always agree, and I bet, that if they met, you would have a heated discussion.  If you like to comment on this blog post, please do, because there is always more to learn.

Part 2 of this series on compost will discuss the variety of compost bays and bins people use, and what equipment and gadgets some of our members find useful in the composting process.

Happy composting


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