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Raised Bed Liners



  • Goose2k7Goose2k7 Posts: 14
    You got me there dancing with herbs it certainly seems to be getting wetter! Mind you I was at Fort William in June for the downhill mountain biking and there was a surprising amount of snow still on the peaks!
  • DovefromaboveDovefromabove Posts: 87,878

    I did lots of research and took lots of advice and in the end my thinking was along the same lines as Busybee - keep the damp away from the inside and let it dry out from the outside.  

    I didn't use plastic on the base - I used a thin permeable membrane so drainage wasn't affected - what it did do was prevent the topsoil washing out of the bottom of the beds - something I'd seen happen before - and the beds drain well.

    I filled the beds with an approx 50:50 mix of organic manure and good topsoil, and there's certainly no shortage of worms in there.  image

    Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.

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  • Busy Bee2Busy Bee2 Posts: 1,005

    I don't know how to explain this, but my liners go down the inner side of the raised bed, under the scaffold board, across to the next bed and up the inside of the board opposite, then gravel is put over the plastic to form a path between the beds.  This prevents the soil from washing out the bottom of the bed because it can't escape, although the prime reason was that all the gravel paths here have to have plastic beneath, because the weeds are so virulent. 

  • I can't understand how the soil escapes when the whole bed is on the ground.  Maybe in the very beginning but then you could always make a bit of extra effort tramping down the soil near the edges to compact a bit.  It will also depend on the type of soil you are working with I suppose. Surely within a few months the soil in the bed and the soil in the ground underneath have knitted together by roots and worms.  As Busy bee says, if your place is very very windy and dry then polythene inside the boards would help hold in moisture. I must admit that the soil near the boards is always dryer than in the middle, so the wood does suck up some moisture. Like Busy Bee2 I also have horticultural fabric between the beds with gravel on top to make tidy paths.  My main difficulty was with sourcing untreated or environmentally friendly wood for the raised beds. As the treatments used in wood preservers are very toxic.  Not really what you want in an Organic garden.

    About liners: I would not like to cut off the the soil in the bed from the earth underneath with a liner as I think the soil would loose its vitality much quicker and die and dead soil is not healthy soil and will not give you healthy crops.  Landscapers all primarily thinking about the "look" and not usually about the health of the crops.

  • BoaterBoater Posts: 241

    For veggies it is probably best to use untreated wood, so it will rot eventually.

    My solution was to use old joists, which may or may not have been treated but unlikely to have any residue to leach out now. Untreated 6x2 joists should take a few years to rot out!

    If you have some kind of reasonable soil underneath (it can be quite thin under a lawn - I get about 1.5 spade depths before I hit rocks and clay) I would mark out the footprint of the bed, dig it 2 spades deep (if possible, less if the soil is not so good), temporary lift out the soil to a couple of inches deep and level the shallow pit, then position the bed so that when you refill it, it will be sunk a couple of inches below the turf level. No liner required.

    Soil cannot escape underneath, worms can get in, long roots can get out, excess water will seep out between planks, the sun will warm the bed quicker than the ground and you can work you patch at a comfy height.

    Every few years you may have to replace or repair a bed, but you might be surprised, where the soil sits tight against the timber lack of air may just prevent rot from living there and attacking the timber - my beds are too young to say from experience!

    If you are going to fit a plastic liner in a raised bed, you might as well use growbags and fit skirting boards around them for appearance image Now there's an idea - I had a spare bag of compost I decided to cut the side off and sow some carrots in (for baby carrots, hopefully there is enough depth for that, they certainly won't grow full size!), it looks a bit ugly, maybe I could clad it to improve the appearance....

  • Goose2k7Goose2k7 Posts: 14
    Thanks for all the advice guys some good ideas and thoughts to take away there!
  • I know this an old thread, but with some 8 years of raised vegetable beds, about 30 inches high, I am increasingly of the view I should line.

    despite a decent loam, they do drain/ dry out quickly.  I thought of pond liner with a drainage/ worm slot about 3 inches wide in the base?

    Suggestions/ experience welcome.


  • BobTheGardenerBobTheGardener Posts: 11,384

    I use compost bags (of which I always have plenty!) turned inside out so they appear black.  I overlap them, stapling them in place on the inside of raised planters using galvanised staples.  Some of my planters made from pressure treated timber are well over 10 years old and the wood is still in good shape.

    A trowel in the hand is worth a thousand lost under a bush.
  • Thanks for the fast Comment Bob. / that's helpful and yes I too have some sack (and one tonne grab bags that might work)

    my challenge is moisture retention rather rather than protection as the beds are made of sleepers , are still weathering well ( + no contamination as far as I'm aware).

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