When choosing wood to use in your garden, be it for decking, trellises, fences, furniture or a shed, there are some key issues to be aware of.
The first is the kind of wood being used and how it has been produced. Garden furniture in particular has been made using wood from some of the most vulnerable forests in the world, the tropical rainforests; wood from poorly managed western red cedar forests in Canada is also commonly found in garden products. So it is important to find out if the wood has come from a sustainable source.
Just asking your retailer or manufacturer may not be the answer. A recent survey by Friends of the Earth and Global Witness showed that most retailers and suppliers do not know where the hardwood garden furniture they sell comes from – and still fewer know about the social and environmental impact of these products. The most reliable way of checking out the wood you buy is to look for products that carry the Forest Stewardship Council (FSC) mark. This is an independent guarantee that the forest or woodland of origin is managed according to agreed social and environmental principles and criteria. These include the concept that forest management 'shall conserve biological diversity and its associated values, water resources, soils, and unique and fragile ecosystems and landscapes, and, by so doing, maintain the ecological functions and the integrity of the forest'.
Plenty of retailers make green claims for their wood furniture but the FSC scheme is the only credible certification for wood products.
The second major issue of concern when it comes to wood in your garden is the use of wood preservatives, such as creosote. Used to prevent rot and decay by bacterial and fungal agents, preservatives are commonly used on fence posts, compost boxes, bed edging, fence panels and sheds.
The most dangerous preservative for the environment is creosote, which leaches into the soil, gives off vapours for seven years and is harmful to people and animals. CCA-treated timber - sometimes called 'tanalized' timber or 'pressure-treated' timber - can also pose a risk to the environment since it uses incredibly toxic chemicals such as copper arsenate. These chemicals are meant to stay in the wood once dry but American researchers have found traces of arsenic in the soil and on the hands of children who have been playing on equipment made from this timber. There may be a danger to you if you fail to use gloves when handling the wood and a mask when sawing it, and certainly this wood should never be burned.
There are other preservatives available, such as those based on boron and acetypetacs zinc and copper, which are all said to have a low toxicity to plants, humans and animals. There are also an increasing number of plant-based preservatives on the market, although these will not necessarily have been endorsed by organic gardening groups. But even these preservatives should be used only if essential. It is better for you and the environment if you avoid the need for any preservatives by taking the following steps:
• Set posts in concrete or use metal 'shoes' for fence posts as the main area of decay is likely to be where the wood meets the soil and air.
• Oil wood that is in contact with the soil -linseed oil is easy to apply and allows the wood to breathe, avoiding trapped moisture.
• Choose the right wood for the job - without preservatives, oak, sweet chestnut and western red cedar will last 20 years in contact with the soil, and untreated pine and larch will last five and ten years respectively. Heart wood and well-seasoned wood is more resistant to decay.
• Consider whether you need to use preservatives at all - most wood will not decay for years anyway and does it matter if wood used on bed edges and compost boxes eventually decays?
• Most wood sold for outdoor use in garden centres and large do-it-yourself stores will have already been treated so if you want to avoid them opt for wood sold for indoor use or visit your local sawmill and ask for untreated wood.
• If you want a green easy life, avoid wood altogether and choose 'wood alternative' instead. Made from recycled plastics, this synthetic wood is now used to make fence posts, panels, trellises, bed-edging boards and boards used in garden benches. With no need for preservatives, stains or paints, this option could be the easiest and greenest going and should be available from a large do-it-yourself store or garden centre.