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which wood for raised beds?

Last post 03-04-2009 4:09 PM by Andy. 6 replies.

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  • 11/02/2004 05:39 PM
    • timy
    • 02 Nov 2004
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    I am planning to put wooden raised vegetable beds in my garden. I have searched the web for details how to do it but have come across a huge debate on what types of wood to use. Some say pressure treated wood is ok and you can even use gavel (bottom of fence) boards. Others say you should'nt use treated woods as the chemicals will affect the plants. Can anybody please give me a steer or let me know what wood they have used

    tim youngman
  • 19/11/2004 10:21 PM
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    The bogweevil says: There is no evidence that wood preservatives will ooze far into surrounding soil if at all, and currently available ones are fairly harmless. Gardeners of a nervous disposition can line their timber with polythene sheets, available from DIY superstores, on the soilward side. You might be reassured that the EU has banned the sale of wood preservatives and treated timber containing chromium, copper and a highly poisonous metaloid (whose name is deleted by the RHS bulletin board software because some of its letters spell a rude word for the fleshy part of the human body on which one sits!) However, if the timber rots, so what (as long as it is cheap)? I use birch tree trunks available locally, which last for over five years before they become compost. Local sawmills, forestry offices and wildlife trusts might be able to help supply untreated timber. Boggy

    Beware the bat-eared bogweevil
  • 24/11/2004 09:13 AM
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    • Obelix
    • Belgium
    • 24 Nov 2004
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    We used railway sleepers as a 3'6" wall on one side to hold up the soil and create a level area and lined them with black plastic to keep water out of them and gunge from them out of the soil. We then used ordinary planed planks and 2" posts painted with water-based cuprinol to build the beds themselves. Old scaffolding planks are also good - if you can get them - but I would treat them to a feed of linseed oil first to make them last longer.

    Obelix - Belgium
  • 25/11/2004 09:45 PM
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    • ipt8
    • 22 Nov 2004
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    As a forester who in the past operated a Tanalith plant (tanalised timber), I can advise that such timber is fine. The suppliers of chemicals to the plant say that once the chemical, which is impregnated under pressure, has dried it is safe to use. Sleepers or creosoted timber is not advised. This is because the creosote can weep from the timber in hot weather, which is messy, and the chemical is harmful to plants. In fact the sale of sleepers to the general public has now been banned (I believe), I presume due to possible health risks. If you want a no chemical alternative that is longer lasting see if you can get oak or sweet chestnut timber which is longer lasting than non preserved softwood timber without treatment. Some softwoods such as Thuya Plicata and Larch have a naturally durable heartwood, but I doubt you could get a piece of timber with only the heartwood present. Ivor Terry

    I P Terry
  • 27/03/2009 02:34 PM
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    • russian
    • Hants
    • 25 Nov 2008
    • 27
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    Thanks everyone,especially the last answer was very informative.  I got quoted £670 for green oak as opposed to £337 for the tanalised softwood option so I feel happy now that there is nothing wrong with the softwood and it's cheaper.  The reason it needs to last a while is because of the labour cost to build it on our steep slope with hard soil!
  • 27/03/2009 06:43 PM
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    • old_iron
    • surrey
    • 27 Mar 2009
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    just built mine from two layers of 4inch sq pressure treated posts from Jewson - £120 for the two beds, 3m by 2.4m

    avoid creosote etc,although it is NOT illegal to sell sleepers, they're likely not to be very square and so can be a pain to lay solidly

  • 03/04/2009 04:09 PM
    In reply to
    • Andy
    • Frinton
    • 03 Apr 2009
    • 19
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    I created all my raised beds from 3x3 posts and 12ft gravel boards.

    The 12ft boards cut nicely to make 8ft long by 4ft wide beds, which mean you can easily reach the middle! An 8 ft post cut in four makes the corners. Some centre bracing (i used some offcuts from a 3x2 rafter) is useful downteh long sides.

    I used 6 lengths to create beds that are quite tall but as i am on solid clay it definitely needed it. The old turfs went in the bottom as they rot down and release nitrogen over time. The rest was filled with a mix of the skimmed off topsoil, homemade compost, and some good old manure. I left some space so they can fill up over time and also cut the posts higher than the  top plank so that i can easily add netting or fleece.

    I have some pictures on Flickr if it helps:

    http://www.flickr.com/photos/willie266/2978975414/in/set-72157608418258202/

    I would advise checking out the local builders merchants as the gravel boards cost me £8 each and the post was £7.

    In terms of the treated boards vs untreated, these are treated and have shown no signs of harming the crops at all. Most seriously toxic checmicals are now banned and the only real no-no is old railway sleepers which would have been tarred, which WILL leach out, especially in hot weather.

    I have even started building more and am now using a 6ft square design for fruit as a cage will fit nicely over my blueberries!

     

    I just knocked up a quick blog post to cover it with some pictures:

    http://www.wired-on-sea.com/