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Has anyone used decking boards for make raised borders? I have started to use them, but have read on this web site http://www.allotment.org.uk/articles2/How_To_Build_a_Compost_Bin.php, "Do not use pressure-treated wood, as it has poisonous levels of copper and chromium, and there is evidence that arsenic can leach into your compost." The boards I am using are "pressure treated with a copper-based wood preservative". Could I use them if I line the inside edge with polythene, so that it isn't in direct contact with the soil? Sorry if it seems I have answered my own question, but just wondered if anyone had used them with no ill-effects to plants/soil. If they are bad for the garden can anyone suggest a cost effective alternative. Thanks
Hi Lorraine, That is an old article. You can no longer buy pressure-treated wood containing arsenic and chromium as they have been banned for such use. It doesn't help that authors of articles on the web rarely put a date on them! Here's a more up to date one:
Just about everyone (including me) uses pressure-treated softwood timber for building raised beds and planters as untreated wood will rot in very short order, unless it is one of the more rot-resistant hardwoods, such as oak, cedar or redwood etc. Those are all prohibitively expensive for many of us though.
Your idea of lining it with polythene is a good one. I would also recommend painting it with a water-based wood treatment such as fence paint. Look for a waterproof one as that will help seal it against any possible leaching of the miniscule amounts of copper which are used in the pressure treatment.
I've also read that if you paint the outside with black bituminous paint, slugs and snails won't cross it into your bed. Rather than line with polythene, I'd use weed membrane, that will let water through, otherwise you'll need to make some holes in your polyethene to let water out, should we have another 'summer' like last year (heaven forbid!), then your beds won't be waterlogged.
I lined the sides of my raised bed with polythene, but the bottom with weed membrane to let water out without washing the compost out of the bottom of the bed.
Surely if you lined the sides of the bed with weed membrane you wouldn't be keeping the wooden sides dry
Thanks your advice everyone - its a releif to know my time and week long aches haven't been for nothing .
Bob - yes it is irritating that websites don't update info. Good thing you and other 'wise owls' are there and keep us informed. Thanks for the link.