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new raised bed

I have just made some raised beds and have clay soil under them. As a novice gardener, do I need to line them with membrane and plastic at the sides , before filling them? I have treated timber which is 48mm thick.?


  • ThankthecatThankthecat Posts: 421
    I'm no expert, but I would say no you wouldn't want to line the beds, just perhaps break up the clay and incorporate as much organic matter into it as you can and then fill the beds with compost / topsoil. 
  • ErashaErasha Posts: 52
    @jan62 153 I have just done the same, for what's it worth I opted to give a few licks of wood paint onto the treated wood then did exactly as thankthecat said
  • BobTheGardenerBobTheGardener Posts: 11,391
    Speaking from personal experiance, I'd say yes, line the sides (only, not the bottom) with plastic which will prevent the direct soil-to-wood contact which makes even treated wood rot quickly.  I use overlapping, inside-out, compost bags stapled to the inside walls using galvanized staples.  The first raised beds I made without doing this only lasted about 3 years.  The lined ones I've built since are now 7yo and still going strong.
    Definitely break up the soil in the base before filling as TTC says though as this will improve drainage. :)
    A trowel in the hand is worth a thousand lost under a bush.
  • Blue OnionBlue Onion Posts: 2,942
    Depends on how much work you want to do.  Being more of a lazy sort, I would line the board with plastic, as Bob described, then cover the bottom with cardboard and newspaper, etc.  Then fill with whatever you have planned.  The worms will do the hard work for you.  I did that on my raised beds.. and last year I dug deep to plant some potatoes, and you could see all the lines from the worm trails as it was a different color from the original base soil.  If you're worried about it, do a nice double dig.. but as a raised bed, the drainage shouldn't be an issue, so I would go for the easy option.. I did. : ) 
    Utah, USA.
  • PosyPosy Posts: 3,601
    I can confirm that your wood will rot, but sections are easy to replace. My daughter's garden has a raised border with sides lined with quality plastic liner. Over the years the liner has been caught with garden tools, pierced by roots and sharp stones and damaged by age. It has shredded into pieces which become mixed with the soil and can now never be effectively removed unless the whole bed is emptied and sieved. I don't believe this is environmentally friendly and it is certainly a real nuisance. Having seen it, I wouldn't line the sides at all.
  • NollieNollie Posts: 6,779
    I had 38mm unlined treated timber raised beds in my old allotment that lasted well over 5 years, so unless you are in a really wet part of the country I reckon your 48mm should last longer without plastic lining. I didn’t bother lining the bottom of my raised beds on clay either, just broke it up by mixing in loads of manure and compost and then topped up with more compost. Clay is hard work, but it is full of nutrients that your veggies will love. The only thing I have never successfully grown is carrots, except the round Paris types. For my raised flower borders I dug in loads of grit too.
    Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
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