Carnaun School Organic Diary April 2005

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Compost is ‘Not all a load of Rubbish’ Cáit Curran, Editor ‘Organic Matters’, Organic Vegetable Grower and Consultant, tells the Carnaun school children

Suddenly everyone is talking compost and in the past week alone I’ve had four queries from customers and neighbours, all asking the same question: “How do l re-cycle my organic waste?” The recent introduction of pay-by-weight refuse charges is causing most households to seriously review what they send to landfill.

Composting has always been a central principle of organic gardening but even many experienced gardeners will admit they make poor compost. Doing it right takes a little effort but it’s not difficult and the good news is everything breaks down eventually no matter how badly you do it.

Good compost is gold dust in your garden. It promotes a rich and diverse microbial world in your soil that will ensure healthy and productive plant growth. Compost becomes humus in the soil and this magic substance has the ability to retain moisture and improve soil structure.

Compost can be made in different ways. The average sized garden or household produces a limited amount of waste material regularly and this can simply be added to a pile on an ongoing basis and it will break down slowly over a period of time. However, during the summer months a lot of garden waste should be available and this is the ideal time to build a compost heap in a single operation.

Good balance

The most important factor in how well your compost breaks down is a thing called the carbon to nitrogen ratio. This is simply the balance of dry, fibrous materials with wetter, softer growth. A good way to visualise this is to imagine a heap of freshly mown grass clippings sitting beside a bale of straw. The grass is soft growth, full of nitrogen and will begin to rot down immediately and will turn into a slimy heap in a few days in warm weather. The dry and fibrous straw, on the other hand, will just sit there for a few years before it begins to slowly break down. Getting the balance of these ingredients right in a compost heap is the key to success.

The general rule is, the tougher the material you put in the compost heap, the longer it will take to break down. Shredding woody plants and prunings will greatly speed up the process. Sufficient micro-organisms and bacteria need to be present in the heap to break down the material. Visible organisms such as eelworms, ants, beetles and particularly earthworms also play a major role. They need air and moisture to do their work.

Big is good

To construct a heap, you need to assemble as much of the materials listed as you can get. The bigger the heap the better it will heat up and break down. Begin with a layer of the tougher material on the bottom that will carry the weight of the heap and allow air to circulate. Follow that with a softer layer such as grass clippings. Alternate the layers and sprinkle with water if the material is dry. An activator which speeds up the de-composition process can be added at intervals. This could be a thin layer of seaweed or poultry manure. Cover the heap when it’s finished to insulate it and keep out the rain.

What goes on the heap:

Garden vegetable waste such as harvested brassica stalks, corn plants, pea and bean plants etc

Weeds, particularly soft weeds pulled before flowering

Shredded newspaper, preferably soaked in water


Soft prunings and small branches that have not become woody

Wood ash in moderation

Tea leaves and coffee grounds add nitrogen

Manure, lime or seaweed in moderation as an activator

Comfrey leaves add potassium

Leaves in small quantities

Don’t use:

Kitchen scraps should go in the worm bin

Coal or peat ash

Coloured paper

Dog and cat faeces

Diseased plants

Weeds that have gone to seed

Persistent weeds like couch grass and nettles

Disposable nappies

Prunings with thorns

Tough green leaves

How you know you’ve done it right

Steam will rise from the heap within a few days as the temperature hots up. The centre of the heap can get as hot as 60 degrees. Check the temperature by pushing your hand into the heap of have a stick in it that you can remove. When the heap cools down it will shrink rapidly to about a third of its original size. More organisms will move in to continue the de-composting process. After a fews the heap can be turned so that the material on the outside is put in the centre to continue the breakdown.

When the compost is ready to use it is dark brown and crumbly.


Compost containers

Larger heaps can be made free standing but in small gardens a bin of some sort to contain the compost is neater. The choice is up to the individual but a bin should be a cubic metre in size for the compost to heat effectively. Bales of straw make excellent containers for compost if built in a box shape. The straw will eventually become part of the compost.

Worm bins

Putting household scraps and food waste on the compost heap is an invitation to vermin to move in so these items should go into the worm bin. There are a number of companies selling expensive bins but a plain black dustbin will do the job just as well.

Worm bins are most useful close to the house where they can be replenished regularly so it’s vital that they don’t smell or attract flies. First drill a set of holes around the perimeter at the bottom of the bin. They will be used for drainage. Then add a few shovels of gravel to cover just above the level of the holes. A divider of some sorts   between the gravel and compost will ensure good drainage and prevent the holes from becoming blocked. I use a circular wooden board.

When this is in place over the gravel simply add a few shovels or organic compost or material from the compost heap. A good population of breeding worms to munch through your compost is the key to success in a bin. You can buy these or pester someone, you know, who has a manure heap to give you a bucket of compost with lots of worms crawling around in it. These little guys are called brandlings and look like a smaller, redder version of earthworms. Left to their own devices and given the right conditions they will continue to demolish all your household leftovers turning them into wonderful brown compost. Put them in the bin and begin adding household peelings and scraps.

Be sensible about what you put in the bin and use the list above as a guide. Worms gone digest bones so give them to the dog. If the bin gets smelly and too wet it means that too many acid foods like orange peelings are being put in and drainage is bad. Fluff up the contents occasionally and add a few handfuls of lime or calcified seaweed to keep it sweet smelling. Don’t leave a black dustbin sitting in full sun in summer or your worms will cook. Runoff from the bin can be collected if you place it on blocks and put a container underneath. Use this as a liquid plant feed.

The average household will fill one bin with compost in the course of a year. When it begins to fill to the top remove the top undigested layer and begin a new bin. This compost is extremely rich and is ideal for potting on plants mixed with bough-in compost.


More Articles –  Carnaun School Organic Garden 2001 – 2007

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About this record

Written by Cáit Curran

Published here 20 Feb 2024 and originally published April 2005

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