Building a garden over concrete

Discussion in 'Planting, growing, nurturing Plants' started by dev, May 7, 2008.

  1. dev

    dev Junior Member

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    Hi, I live in inner Sydney in a terrace house and my backyard is covered in concrete except for a small 20cm x 3m patch against the back wall which gets no sun. At the moment I am growing all my fruit/veges (tomato, eggplant, spinach, limes, mint, basil and chillis) in pots lined up against the side wall as this is the spot that gets the best sun. I wanted to turn the space where my pots are into a garden patch about 50cm x 4m without having to dig up the concrete and was wondering if anyone has done this before? Mostly wanted some recommendations on reinforcements to hold the soil, soil depths I would need and whether I should put something down like newspaper before the soil. Also the ground slants so potentially the water and soil may escape down the side path... Thanks.
     
  2. ppp

    ppp Junior Member

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    Re: Building a garden over concrete

    do you own or rent?

    I guess I'm asking how permanent you want it...
     
  3. dev

    dev Junior Member

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    Re: Building a garden over concrete

    I am renting off my girlfriends parents so it can be permanent, they have more or less given me free reign with the outdoor space.
     
  4. SueinWA

    SueinWA Junior Member

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    Re: Building a garden over concrete

    I saw in a magazine where someone had built some raised beds for handicapped people. The beds were about 8" (20cm) deep, with room for someone in a wheelchair to roll right underneath.

    I would think that building a frame around or on top of the concrete would be almost the same. Make it about 8-10" (20-25cm) deep. I wouldn't bother with laying newspaper down, but you might want to make a liner of that permeable landscape fabric that goes up the sides so you don't keep losing soil from the crack where the frames meet the concrete. I would fill it with high-quality soil and compost --- since your plants won't have the usual access to deeper soil with natural nutrients.

    You might want to add some dolomite, rock powders, bone meal, wood ash, etc, to make sure your food crops have a decent set of nutrients. And keep it mulched, too.

    Sue
     
  5. dev

    dev Junior Member

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    Re: Building a garden over concrete

    cool thanks for the advice sue.
     
  6. ppp

    ppp Junior Member

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    Re: Building a garden over concrete

    I would be tempted to try your hand at brick laying!
    You can buy concrete blocks for around $3-$3 each. The "half" blocks are (I think) 100mm x 400mm or the full size ones are around 200mm x 400mm. The later would obviously be more stable, and easier to also serve as a seat on the edge of the garden. What about a ~600 - 800mm high wall (3-4 blocks high) filled with soil. For a 3m x 0.5 m x 0.6m bed I estimate you would need no more that 35 blocks (~$105). You'll need to ensure you have a good stable base and mix up a cement mortar to stick them together.

    Last only time I bought soil I think we paid ~$60 per cubic metre. So for your 0.5 x 3 x 0.6m garden that would be 0.9 cubic metres (or ~$60). Just a warning that the soil you buy like that is far from fantastic. You will need to add mushroom compost ,manure, compost etc. So perhaps you would be better getting 0.5 cubic metres delivered and buy up big on the mushroom compost, manure, etc.

    You will want to prevent too much moisture moving into the house. I will leave this to other people who have more experience?? But I'm thinking a heavy black plastic will be needed. Some drainage holes on the side away from the building will also prevent moisture moving into the house by draining it before the water ponds.

    Just some thoughts....

    PPP
     
  7. dylanz

    dylanz Junior Member

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    Re: Building a garden over concrete

    I know Bill did a parking lot type garden in Melbourne somewhere, and this is (roughly from memory) what he did:

    1) Throw down tons of hay/straw, probably a good meter deep.
    2) Soak it with tons of water
    3) Get good compost, and make small compost lenses (like this text, but flipped horizontally... () ...)where you want to plant.
    4) Plant
    5) Repeat 2-3-4 as your heart desires :)

    Know he successfully had tons of potatoes, carrots, and a bunch of other good stuff.
    Eventually the hay/straw breaks down, and will result in soil (over years).

    This process saves you from having to buy tons of expensive compost, and, you get large initial yield.
    Apparently the site of the parking lot is now just a fertile garden... and the average joe would never know there is concrete underneath.

    Been meaning to try it out... but need some concrete to work with !
    Cheers !
    ==
    Dylan
     
  8. barely run

    barely run Junior Member

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    Re: Building a garden over concrete

    My raised beds are sheets of heble concrete....each piece is about 2.4m and halved one for each end. Screwed together with angle iron. Cost out here in the bush $176 should be cheaper in the city. filled it as NO Dig...3 bales straw,some grass, chook poo, and one trailer load of compost from local sheltered workshop who make it. Layered with compost on top. Is working well so far.
    Cathy
     
  9. ppp

    ppp Junior Member

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    Re: Building a garden over concrete

    barely run Hey, with buying in the city verses country, my experience is that most things like that are much more expensive in the city.
    I head out of the city to a nearby semi-rural town rather than in to bunnings to buy as much stuff as I can.
     
  10. dev

    dev Junior Member

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    Re: Building a garden over concrete

    Excellent you have all given me some great ideas and I have a heap of sugar cane mulch which I am thinking might work well if mixed with some compost and soil. Not sure if I feel confident enough to mix up a cement mortar but I was thinking if I can track down some interlocking bricks that would be ideal. I might document the process and post some photos when I start. The drainage issue is the biggest thing I will have to focus on and a black plastic sheet with drainage holes should do the trick hopefully if I lay enough mulch at the bottom that will absorb some of it and help the mulch to break down...?
     
  11. Comfrey

    Comfrey Junior Member

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    Re: Building a garden over concrete

    I've done raised beds using bessa bricks (how do you spell that? I mean the large grey concrete sort) no mortar, lined with black plastic with holes, in rented accommodation, walls two bricks high. Inexpensive and easy.
     

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