Treated wood and raised beds the RHS & WPA way
The Royal Horticultural Society (RHS) says that raised planter beds are becoming increasingly popular because they are good for:
• Improving drainage
• Increasing soil temperature
• Improving access
• Growing plants in a different soil type
Wood is by far the most popular material for raised bed and other garden landscaping construction. It is light, easy to work and install and is low cost compared with other materials. The most cost effective way to ensure that the wood remains structurally sound and free from rotting long term is to use wood that has been pressure pre-treated in an industrial wood preservation plant. Pre-treated wood is widely available from timber merchants or DIY stores and needs no further protection during its life. The wood preservatives used in pre-treatment plants are approved for use by the Health & Safety Executive and there is no restriction on the use of pre-treated wood for things like compost bins, planters and raised beds for vegetables. The RHS is very clear that treated wood is suitable for long term structures in the garden. And their web site offers the following guidance: "Modern wood pre-treatments do not contain potentially harmful heavy metals, so are safe to use." A champion of organic horticulture, the Soil Association also states that if the timber used for organic vegetable beds is preservative pre-treated then there are no issues in terms of organic status.
To maximise service life the Wood Protection Association (WPA) recommends that wood intended for direct soil contact be pressure impregnated in accordance with British Standard 8417. This standard requires a minimum service life of 15 years for timbers that are to be in permanent contact with the soil and fresh water. The WPA also says that to ensure the correct level of protection is achieved only buy treated wood from timber treaters who provide evidence that the wood is suitable for direct soil contact. A treatment certificate should be requested or buy wood that has been produced under the WPA Benchmark quality scheme for absolute reassurance that the wood will provide a long and trouble free life.
For the RHS Top Tips on building raised planters click or paste into your browser the following link.