The beginner’s guide to compost

Why compost?

An average Auckland refuse bin contains 40 per cent food waste and 10 per cent garden waste. With more councils charging, or planning to charge, for rubbish removal, the simple act of composting can save you half of your rubbish removal costs. Compost is great for soil and reduces the need for chemical fertilisers. It also keeps organic waste out of landfills, which is a pressing issue: waste that rots in landfills generally breaks down anaerobically (without oxygen), creating the potent greenhouse gas methane.

Bokashi

This is a system that takes up very little space, doesn’t smell, is quick to produce compost and is cheap and easy to set up and maintain. Bokashi was developed in Japan where most of the population live in small apartments.

Benefits

• Quick, cheap and easy 
• Needs very little space 
• Odour-free
• The liquid that drains from the food waste is a great fertiliser (when diluted) and can also be poured down drains to clean them

Considerations

• If you have a large household with a lot of food waste you may need more than one two-bucket system, or use bokashi in conjunction with other composting systems. Industrial-sized systems are available for businesses and schools
• Dogs can be attracted to the compost for up to a week after it’s buried but you can fix this by placing a cover or wire netting over the area

How does it work?

Bokashi is a two-bucket system of microbial composting. Each bucket is a set of two – one smaller bucket with holes drilled in the bottom sits inside the other, which is then sealed. Food scraps are added with regular amounts of sawdust that contains micro-organisms that ferment or ‘pickle’ the waste. When the bucket is full it takes about three weeks to produce a nutrient-rich compost that is perfect fertiliser for all types of plants and gardens. Meanwhile, you use your second bucket to continue collecting food scraps.

What do you need?

Purchase a bokashi system – bucket and composting sawdust – from www.zingbokashi.co.nz from $55. One bag of sawdust, which costs around $10, will last an average four-person family eight to 10 weeks.

Some councils also sell bokashi systems at subsidised prices. Otherwise make your own bucket system for around $30 by sourcing a food-grade bucket with a strong seal and putting another bucket inside it, with holes drilled into the bottom. Food-grade buckets start at around $9 at www.plastic.co.nz or you could ask your local café or restaurant for any empties they no longer need. You can even make your own sawdust mixture (using sawdust, bran, molasses, water and those handy micro-organisms), but it may be cheaper and easier to buy it ready-made unless you are making large quantities.

Getting started

Sprinkle one tablespoon of sawdust in the base of your bucket. Add a layer of food – remember to break it down into small pieces. Once you have a layer about 3cm deep, add another tablespoon of sawdust. Squash food down gently to remove any air (a potato masher is ideal). Close the lid tightly, and try to only open it twice each day.

What can you put into bokashi?

• Most types of food waste, including meat and cheese

What can’t you put in?

• Milk, too much liquid and large chunks of vegetable matter (chop it up first)
• Paper, large bones (small are okay), oils, citrus, seafood shells

How do you keep it going?

Keep your bucket in a warm place but out of direct sunlight, for instance in a hot water cupboard or the laundry. Drain any liquid that forms in the bottom of the bucket every 2-3 days. When the bucket is full, close the lid airtight and keep in a warm place for seven to 10 days in summer months and 10-14 days in winter.

How do you know when it’s ready?

When it smells like pickles or sweet vinegar, it is ready to be buried 30cm deep in the garden.

2. Worm farming

Worm farms provide a home for a colony of worms – usually tiger or red varieties – that eat your food scraps, turning them into a very rich soil. The worms also excrete ‘worm tea’, which is an excellent fertiliser.

Benefits

• Although worm farms vary in size they generally take up little space
• Constant supply of fertiliser

Considerations

• Worms need moisture and regular feeding so can’t be left unattended for more than a few weeks
• The farms can be expensive
• Worms will breed although it’s easy to either increase your worm farm or give away the excess worms
• Worms can’t take large amounts of food at once, which means if you overfeed them the extra food may rot and create odour
• Worms don’t like very cold or hot temperatures (10-30°C)
• Sometimes it’s difficult to get the balance of food, temperature, moisture and acidity right
• If your worm farm gets too wet it could turn anaerobic and start to smell

How does it work?

A worm farm is essentially a system of trays stacked on top of each other – usually about three to five. There is a tap or draining facility on the bottom tray for the worm tea, and ventilation holes in the top tray. Once a tray fills up with vermicasts, it is removed, emptied and the other trays are rotated to encourage the worms to migrate to the next level. The worms need a sheltered dark spot away from sun, wind and rain with good air flow: a carport or sheltered deck area is ideal.

What do you need?

Building your own worm farm is by far the cheapest and most eco-friendly option as you can use recycled materials.Simple instructions for building a tyre worm farm can be found here. For this kind of farm you’ll need:

• Old carpet or sacking
• Phone books or bricks to keep it raised
• 60cm square piece of corrugated iron for the bottom
• 3 car tyres (same size)
• Lid – old wood is fine
• Lots of newspapers – at least 30
• Old pot or bucket
• Small piece of polythene wrap
• Worms – a 250g box is around $30 – try www.wormsrus.co.nz

Otherwise a ready-made worm farm for an average household costs around $160 from www.earthlydelight.co.nz.

What can you put in?

• Most fruit and vegetable waste including coffee grounds, teabags and crushed eggshells
• Paper, vacuum cleaner dust, hair

What can’t you put in?

• Meat and dairy products
• Spicy food, chilli, citrus
• Flour and flour products
• Woody garden waste
• Shiny paper

How do you keep it going?

Feed your worms the food scraps they love – you can start with around 250g per day and gradually increase the amount as the worms breed and need more food.

How do you know when it’s ready?

Once your bottom tray has all turned to rich black soil, tip it into your garden and rotate the trays by putting the empty one on top. Collect any liquid that drains out in a bucket and dilute about 1/10 with water before using on the garden

3. Traditional composting

In this system food and garden waste is broken down either in a heap or a bin. The compost is often covered with old carpet or a tarpaulin. The layers should be turned regularly to help speed decomposition.

Benefits

• Great if you have a large garden or a lot of food waste

Considerations

• Can be complicated getting balance of materials, moisture and temperature right
• Needs a lot of different materials
• Can attract rodents
• May smell
• Requires a reasonable amount of outdoor space (one to five cubic metres)
• Needs regular turning

How does it work?

The waste decomposes in thin layers of green vegetable matter (rich in nitrogen) and brown vegetable matter (rich in carbon).

What do you need?

Bins are an easy and tidy option. Consider your budget – bins range from $40 to $500 – how much space you have and what waste you want to compost. For a household of two to four people, a bin of 240 litres might be a good size.

If you have the DIY skills, building your own compost bin is a great way to recycle materials such as wood, bricks or chicken wire. For more ideas on how to build your own compost bin or to start a compost heap, visit www.createyourowneden.org.nz.

What can you put in?

• Most garden waste – cut up or mulched for speedier results
• Paper and cardboard
• Ash and sawdust
• Seaweed

What can’t you put in?

• Meat, fish, bones, oil
• Invasive weeds and their seeds, or diseased plants
• Bamboo and large quantities of gum leaves and pine needles

Composting hints

Contact your local council – many offer free composting courses and free or subsidised composting kits.

Some councils have already made the move to collecting food waste from kerbsides, such as Christchurch City Council. Auckland City Council will have a similar programme in place by 2015. But don't wait –  compost your own!