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  1. #1
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    Nov 2007
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    Default Top Soil How deep.???

    Happy New Year all the best for 2008 to all!!!

    I just finished my retaining wall project and I'm now ready to fill it with some small plants. The Garden bed measures 16.2 x .4 meters, How deep should I go with the top soil????. The fill currently is a clay soil, and I was going to use that mushroom compost topsoil.

    Also The retaining wall is bricked and i was going to seal it with bitimun paint before i but the soil in, Do I have to seal it?? and if I do will the paint be enough??

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  3. #2
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    Jan 2004
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    I think around 300mm would be deep enough for plants, perhaps even first digging in a layer of gypsum to break down the clay to assist with drainage.

    From my experience with mushroom compost I find it gradually breaks down and disapates having to be replaced after a couple of years so I think you would be better filling the area with sandy loam and topping the last 100mm with mushroom compost (if you really want) or even a thinner layer of mulch.

    Other far more learned members will assist you with the wall.
    Jack

  4. #3
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    Mar 2007
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    Jacksin's on the money with digging in gypsum. If you don't break up the clay base you might run into drainage problems. Also your plants may struggle if/when their roots hit the clay subsoil.

    When I did my retaining wall I incorporated gypsum, backfilled with an organic loam then put a layer of mulch on top. The plants are thriving.

    Sandy loam in garden beds can be a bit too free draining unless the plants require a loose mix (e.g. succulents, cacti, lawn etc.).

    One word of warning with mushroom compost - it can be very alkaline. If you're thinking of putting in any acid loving plants in the bed (e.g. camelias, azaleas, gardenias) I would advise against using it as a mulch or soil improver. A good organic compost would be a better option.

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