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How to make sure compost heap built into slope can breath?

iamjowilsoniamjowilson Posts: 67
in The potting shed
My garden is quite small, and slopes away from the house. The only (and logical) place to put my new compost area is in the slope at the end of the garden. The sub soil is heavy clay (you could literally use it for pottery).

I’m making a 3 bin system, which will be 75cm tall, and the bottom 50cm will be against the slope, as well as triangles on each side going from 50cm at the back down to 0 at the front. The ‘above ground’ parts will be made from horizontal wood decking, with largish gaps between and lined with chicken wire - so that air can circulate without (hopefully) compost escaping. 

For the ‘below ground’ parts I have three options:
1) wood - same as above ground,?with weed proof membrane between soil and bins. I’m worried the wood will rot very fast though without air flow.
2) same as 1 but using composite decking boards which are a mix of wood and recycled plastic. Not too sure of longevity when in constant contact with soil and compost, with no air flow.
3) concrete paving slabs laid on end. Which is obv best from longevity of structure POV, but is it ok for the actual compost? Will it go anaerobic? 

I really have no where else in the garden to put this, and so unless it’s going to be dire I’d like to stick with the built into the slope plan.

can anyone advise me?
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  • Lizzie27Lizzie27 Posts: 12,494
    The dalek plastic compost bins get no air unless you empty them out occasionally so whatever method you use, I wouldn't worry too much about it. As for longevity, how long is a piece of string? I'd go with whatever materials you can afford and can get hold off. If you're building into the slope, you could just have three sides (unless I've misunderstood your setup).
    North East Somerset - Clay soil over limestone
  • Nanny BeachNanny Beach Posts: 8,719
    you dont want weed proof membrane under compost bins, it is advised you build them on soil, mine are now down the bottom in veg plot, they were halfway down the garden, the green plastic ones, so we have no air circulating, I have to water inside them, or leave the tops off ,around the raised beds is shingle, they are on slabs but full of worms.  What about making them from palletts, (you can find that on utube) I cant explain but that would work on a slope.  Hubby did that a couple of gardens ago.  If you are having them open like this you need to make sure you have a good mix of brown stuff (drier) otherwise it will be a sludgy mess. Both types work perfectly well.I couldnt visulaise it eith Lizzie, we need a picture
  • Hampshire_HogHampshire_Hog Posts: 1,089
    edited June 2019
    Why use anything unless the ground is particularly unstable  I would just excavate into the bank and start putting the stuff in the space, you might want to put something at the front (Old Pallet) but again I would probably just leave it open. 🐗

    "You don't stop gardening because you get old, you get old because you stop gardening." - The Hampshire Hog
  • iamjowilsoniamjowilson Posts: 67
    I am using a structure a) because I don’t want the bank to slide away in the winter, and b) because I want a 3 bin system rather than just one heap :-)

    It will be on earth, but I was going to line the back (so the vertical plane) with membrane to stop weeds creeping in, and also make sure no soil falls in, again in winter when the clay becomes slidey. 

    Rather bad diagram attached! 
  • iamjowilsoniamjowilson Posts: 67
    Oh dear - am out and about and can’t upload pic at the mo 
  • NollieNollie Posts: 7,529
    I would think you would be fine using sturdy wood like scaffolding boards to hold the soil back on the vertical plane, with a breathable weed membrane behind, with the interim dividing supports between the three bays stiffening and supporting it, those attached to posts at each end. I hear the plastic boards warp easily and think they may be a bit thin. 

    Getting air into the compost heap is more a matter of regular turning and a good mix of woody and green stuff, the rougher woody stuff naturally forms air pockets, so I wouldn’t worry about that.
    Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
  • Nanny BeachNanny Beach Posts: 8,719
    weeds dont creep in, if they did they would be composted
  • iamjowilsoniamjowilson Posts: 67
    Ok thanks for all advice 👍
    How about tree roots - will they creep in? There are some tree round about but there’s really nowhere else to site it, at least this year. 
  • TopbirdTopbird Posts: 8,355
    Just to throw my 2 penn'orth in....

    Wood will rot if it's in contact with damp ground.

    Tree roots will probably make their way into the compost bins if there's nice rich, moist compost in there and the trees are close by. The trees may then suck a lot of the moisture and goodness from the compost before you've had time to use it.

    Rodents will often burrow into a nice warm compost heap if they're looking to set up home for the winter.

    For all those reasons I would suggest that (finances allowing) you use concrete slabs (you only need to use the big really cheap ones) to slab the floor of the whole composting area plus the back wall of the bay.

    I have large compost bins on concrete and have never had a problem with vermin. I thought there might be a problem because worms and other critters wouldn't be able to get in and help with composting process. Wrong! - my bins are full of worms and other (good) creatures all doing their stuff (I assume that eggs etc are introduced with soil attached to weeds and other plants). My bins produce usable compost within 6 months.

    The bins are heavy duty plastic which open up completely to allow me to drag the compost out and turn it from one bin into another. That's much easier to do onto concrete slabs. The level slabs also make it easy to get a wheel barrow to the bins, to scrape up compost and to sweep up stray bits and generally keep the area fairly tidy.


    Heaven is ... sitting in the garden with a G&T and a cat while watching the sun go down
  • FireFire Posts: 19,096
    I too would also go for concrete and wouldn't worry about air or critters getting in. I use only plastic sealed rubbish bins with no air vents and they are heaving with every kind of life, worms galore. Concrete, as Topbird says, would slow tree roots and be long lasting. The stuff you create the bins from will not determine whether your compost is anaerobic. That's more down to you. If you are adding lots of chunky garden material then there should be lots of air in the structure, at least initially. A three bin system is good for turning the compost as it cooks, and the turning airs the material. The more you turn it, the faster it will decompose, but that's your call.

    If you want a faster cooking cycle, add in horse manure,  compost you have previously made and/or garden soil. I always mix in the remnants from the cooked and ready-to-use bins to new bin material so to add worms, microrobes and fungi.

    Give a thought to drainage; Bins generate a lot of liquid. Also to rain coming off the slope. Is land slipping an issue?
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