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Is it wise to add sawdust, bark chip or wood shavings to a home composting unit?

Wood and wood waste do rot down, but can take a long time and this is the reason we should be cautious about adding them to a home compost bin.
Different types of wood rot at different rates, so while prunings from fruit trees or sawdust from birch will rot completely within 2 or 3 years, oak, elm and resiny soft woods will take much longer, often 5 to 7 years. This means that everything else in your compost bin will have decomposed and be ready to use long before the wood waste has broken down.
If you regularly have quantities of sawdust, shavings or bark to dispose of it is best to devote a special composting unit to them. This can be a plastic bin or a large New Zealand Box depending upon the volume you have to deal with.
Even if sawdust or shavings have been used as bedding for animals like poultry or horses, the woody element will still take several years to decompose so this, too, is best treated separately.

If you have commercial quantities of wood waste these require special handling. The advice here is for domestic quantities only.

Always ensure that a compost bin for wood waste sits on the soil. In order to break down all the different elements in wood, especially the tough cellulose and lignin, a succession of different bacteria and fungi are needed. These will probably be present in your soil so give them easy access to your compost bin.
As the wood waste breaks down different substances can leach out of it. Some of these can cause problems in streams and rivers so keep any composting wood waste well away from watercourses and make sure that any run off does not get in to drains.

Once your wood waste has completely broken down and looks, smells and feels like soil you can use it in the garden. It will not be high in nutrients but will make a good soil conditioner.

It is possible to use sawdust, wood shavings and bark as a pathing material or as a mulch. It is important that fresh wood waste does not get mixed in to the soil as it can change the chemical composition of the soil and cause problems for plant growth. So it is best to lay a permeable membrane on the surface of the soil and to put the mulch of wood waste on top of this. The mulch will gradually break down over the years, weeds will grow in it and, after 3 or 4 years, it can safely be added to your regular home compost bin.

Treated correctly, sawdust, wood shavings and bark can be an asset to the garden.

Useful links:
Scottish Borders Council: Reduce Reuse Recycle

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