Using wood in the organic garden

In an organic garden the aim is to use wood from sustainable sources, and to avoid the use of wood preservatives. Where preservatives are essential,
the least hamful products should be used. This factsheet follows Garden Organic's Organic Gardening Guidelines.
There are no 'official' standards covering the use of wood preservatives in organic situations.

Where are wood preservatives used in the garden?

Wood in contact with soil or compost - fence posts, compost boxes, bed edging etc.
Wood exposed to the elements, but not in contact with the soil - decking, fence panels etc.
Wood not exposed to the elements - inside a shed for example.

The degree of protection actually required depends on the situation. Rot is most likely to occur where the wood is in contact with both moisture and air - such as where a post enters the soil.

Doing without preservatives

Wood preservatives are long lasting, toxic products. Here are some ways of doing without them:

Choose the right wood for the job (see below).
Does it matter if the wood finally decays? Wood can last for years without any preservatives.
Tree stakes, for example, often only need to last for a few years.
Protect without preservatives : Use a metal 'shoe' such as a 'Metpost' to protect fence posts and other supporting posts where they enter the ground.
Stain, paint or oil wood not in contact with the soil. Raw linseed oil, for example, is easy to apply and can prevent cracking and drying out if applied annually. There is no reason to use preservatives on non-structural and decorative timbers.

� 1996 Forest Stewardship Council A.C.

Durability - soft or hard woods?

Hardwood may last for around twenty years in contact with the ground with no treatment. Most untreated softwood lumber may last around five years.

Hardwoods generally from broad leaved, deciduous trees such as ash, oak, beech, lime and sweet chestnut. Can be expensive to buy, but are ideal where durability is important - for example whenconstructing a bench, or anything else that you want to last. Heart wood and wood that has been well seasoned is most resistant to decay.
Softwood wood from fast growing conifers such as pine, cedar (Cedrus), fir, larch and redwood. Cheaper than hardwood but as its name suggests, not as durable. Red cedar (Toona ciliata) is actually a hardwood, commonly available in timber merchants, and not to be confused with other Cedrus softwoods.

Coppice wood products

Trellis, plant supports, bean poles, screens and hurdles and many other items can be fashioned from wood harvested from UK coppice woods, or from your own garden. This is probably the most sustainable form of wood to use in an organic garden. Treat with linseed oil for longer life.

The coppice products website, www.coppice-products.co.uk, lists UK sources of coppice wood. Bamboo may not be a traditional coppice product in the UK, but canes can be harvested from garden grown bamboo. If not sturdy enough for traditional runner bean poles, they can be used to make trellis and plant supports.

Recycled wood

Second hand or recycled wood can be scrounged - from skips for example - or purchased. It may be difficult to decide if it has been treated.

There are many wood recycling projects across the country, affiliated to the NCWRP. The waste wood comes from construction, demolition, wood products manufacturing industries, and from the domestic waste stream.

Most schemes segregate treated and non-treated timber. Always ask before you buy.
Contacts : www.communitywoodrecycling.org.uk Tel: 01273 203040
Other sources include salvage yards and municipal refuse collection sites.

Buying timber

Organically produced timber products are certified by the Soil Association's Woodmark – an international forestry and chain of custody certification scheme, which is also FSC accredited.

For a list of Woodmark/ FSC accredited timber suppliers in the UK go to www.fsc-uk.org, FSC UK, 11-13 Great Oak Street, Llanidloes, Powys SY18 6BU.

Always try to ensure that wood you buy is from a well-managed, sustainable source. Look out for a seal of approval for sustainability such as the Forest Stewardship Council (FSC) and the Programme for the Endorsement of Forest Certification (PEFC). FSC and PEFC procure wood from worldwide sources so ask before you buy as provenance is recorded. UK or European produced timber is preferable.

Most timber sold for outdoor use may already have been treated and not labelled as such (see below, 'pressure treated timber'). Always ask before you buy. Timber sold for indoor use is likely to be more expensive, but will be untreated.

Builders scaffolding boards, a good buy for bed edging, being sturdy and of a good width, are usually untreated, but always ask. Old railway sleepers were a popular choice but have now been banned for garden use as they have been steeped in creosote. New 'sleepers', with less harmful treatments, are
now available.

A local sawmill or woodyard may sell untreated timber direct to the public. If not already seasoned, it should be left to season before use.

Wood-free 'wood'

Wood alternatives, made from recycled plastics and even concrete are available. They need no preservatives. Fence posts, panels, gates and trellis, gravel boards and boards suitable for bed edging are some of the items available.

Creosote has been banned in the UK since July 2003

Wood preservatives

Creosote: Banned in the UK from July 2003. Do not use materials treated with creosote or use up old supplies. Dispose of old supplies safely, contact your local authority to arrange disposal.
Pressure treated timber: any timber that has been impregnated with chemicals under pressure to ensure full penetration into the wood. Safer alternatives to the Copper, Chrome Arsenate (CCA) treatments that used to be commonly used (now banned for products for domestic use) are now used. Tanalith E ® is a preservative made from a copper and organic biocide (triazole) formulation. Osmose naturewood is timber that has been preserved with Osmose products containing copper and an organic co-biocide.
Boron compounds: Boron compounds appear to have a low toxicity to humans and the environment. Very soluble in water, so for outdoor use boron is applied in the form of glass rods, inserted into predrilled holes in the timber. The minimum dimension of the wood to be treated is around 75x25cm.
Borax timber preservatives can also be painted on for indoor and outdoor use. Glycol borates are only licensed for professional use.
'Natural' preservatives: Plant based wood preservatives are available, that are claimed to be safer to use than the traditional chemical materials. We do not have the information to support or refute that claim. Wood pitch and other products extracted from timber have the potential to be as harmful as coal-derived creosotes.