– By Michael Mobbs  –

Use this table to estimate how much compost mulch you will need for your food plants.

The table will help you choose your composting options. For example, if you want to grow say, 10 citrus trees, you will need about 300 to 800 litres of compost capacity to meet the needs of the trees. A 60 litre capacity worm farm will partly meet the needs of a single young citrus but you’ll still need other fertilisers and mulches to support the young tree.

Each fruit tree needs a lot of nutrients and it’s best to apply fertilizer of some kind four times a year if you do nothing in between. Mulching with compost can help reduce or avoid importing fertilisers like blood and bone and seaweed extract. So composting saves you money and means you import less “stuff” to make your garden grow.

The estimates in the table show the amount of food waste, the number of households and amount of compost and soil created by different composting options. The table shows that to grow food we need many households for each tree and for most households it’s only when they top up their food waste from a café that there will be enough composted soil and mulch to feed your citrus trees. (These are estimates because “households” vary in number and in the type of waste they create; the average Australian household – about 2.2 people – produces over 400 kg a year of food waste.)

Estimates of food waste needed to make soil for gardens

Compost size

Number of households

Amount of food waste day / year

Amount of soil / mulch made in two months

Amount of liquid fertilizer in two months

Number of citrus trees mulched

60 litre worm farm


Less than 1 kg day, 360 kg year

Will not compost citrus, onions

2 – 3 milk crates, less than 60 kgs

About 30 litres

About one every two months

300 litre bin

3 to 4

Less than 2 milk crates a week

About 100 kgs

About 40 litres

About 3 every two months

400 litre bine

6 to 8

3000 kgs a year, or over 2kgs a day or over 3 milk crates a week

1 tonne year, over 85 kgs a month, over 160 kgs in two months or 16 milk crates

About 60 litres

About five to six every two months

Compost tip

Ask the café where you get your food waste to include all its table napkins in the waste; the napkins provide valuable carbon and help to balance the waste and improve the speed and smell of the composting process.

Finally, why compost?

When you compost you make soil. When you make soil you take carbon out of the air. And you stop your waste making pollution such as highly polluting methane from rubbish tips.

In Sydney City, for example, about half the waste goes down a mineshaft near Goulburn and spews up methane and carbon dioxide. Your old couch, computers and stuff left out on the street goes there.

Do you want to be part of that polluting system plus pay rates for the privilege?

Composting, once you’ve got your bins, is free. And it cuts down the fertiliser and “stuff” you would otherwise import for your garden.

Next step is to get whole suburbs composting where they live and work; that’s happening now as gardening is growing hugely and folks are planting food plants which need compost; see the video display above or here for the next batch of  handy lessons and demonstrations in Sydney.

Go on let your squeamishness have a field day – give it a try.

More gardening tips: https://www.youtube.com/watch?v=D7sguN_WLgY

See Michael Mobbs’ web page at  www.sustainablehouse.com.au. His best-selling book Sustainable House, published by Choice, is in its 12th edition: https://profile.choice.com.au/shop/Membership-and-Sales/Books/Sustainable-House.aspx
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