Rehabilitation of asphalt to garden

Discussion in 'HortForum' started by mhillbilly, Feb 13, 2021.

  1. mhillbilly

    mhillbilly New Member

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    I am trying to rehabilitate an area of my property, approximately 1,200 square feet that was paved with asphalt. I have had the asphalt removed and left the 3” or so of gravel because it’s only a little better than the rocky orangey clay soil that’s underneath it. I have started by laying cardboard then logs, branches, sticks and now am piling wood chips on top. The log/stick layer is about 12-18". I think the finished height of the bed should be another 12" or more as the logs etc will eventually decompose and everything will shrink down. The soil on the rest of my property is only about 10” deep before the shovel meets with the rocky orangey stuff underneath which is why I’m trying to build it up with more than just the chips. (I think maybe that when it was logged in the early 20th century that some of the foresty loam may have washed down the hill.) So my question is, should I add more layers of things like manure and cardboard, (compost would be helpful but I don’t have much) or just use wood chips? Should I make more and thinner layers? I would like to plant some native shrubs, rhodos, perennials.
    Thanks!
     
  2. vitog

    vitog Rising Contributor 10 Years

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    The logs, branches, and sticks will take years to break down completely; so, you have plenty of time to build up the soil. I would add something inorganic to promote drainage, such as coarse sand or crushed pumice, to the organic material above the gravel layer. Any available compost or topsoil will help, of course. As soon as possible, you should plant a leguminous perennial cover crop and keep it healthy until you have enough soil for the final planting.
     
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  3. Sulev

    Sulev Active Member

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    Many shrubs, and rhodos should cope with gravel pretty well, so I would plant these right this spring. If you plan to rise the soil, then just make small heaps, and plant on top of these.
    For perennials the same tactics should work, but maybe for some species some local soil amendments (manure, compost, peat etc) should be done before planting.
     
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  4. Acerholic

    Acerholic Paragon of Plants Forums Moderator VCBF Cherry Scout Maple Society

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    @mhillbilly good morning, I think if it were me I would like to help the soil before planting up a garden and as you say you don't have any compost, so how about sowing green manure.
    I could go onto explain, but the RHS does it far better, so here is the link.
    Green manures
    A good garden and happy plants is all about preparation so don't rush the project. The green manure can look very pretty before digging in, so no need to worry about a bland looking patch.
     
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  5. Margot

    Margot Generous Contributor 10 Years

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    Well @mhillbilly - first, welcome to these forums! There are a few variables to consider before you continue on your quest to rehabilitate the section of your garden that was previously covered with asphalt. I can understand why you have embarked on remediation efforts using branches etc. to, in effect, sequester potential asphalt toxins still in the soil from the new growing medium you want to create above ground. There are a couple of other considerations I would suggest depending on a. the size of your garden and b. your age. If the 1200 sq. feet you are wanting to rehabilitate is only a small part of your total square footage and if you still have a decade or more to wait, I think you're on the right course. If, however, this is a big part of your garden and time is of the essence, I'd bring in as much top-quality topsoil as I could afford and create the garden of your dreams now, this year.
     
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  6. mhillbilly

    mhillbilly New Member

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    First of all, thank you so much for your great ideas. My original plan was to try to mimic nature, but hoping to speed things up a little, employing kind of a hugelkultur and lasagna type system of layering but not in high heaps like in hugelkultur. Unfortunately I have already started to spread some of the wood chips around but I am thinking that I will now add some coarse sand and manure to the mix.
    From the suggestions from Sulev I am going to plant some of my rhodos and shrub row plants this spring into the small heaps idea to get them started. And since time is ticking by, I might go the top quality topsoil route for parts of it and plant directly into that and fill in the areas beside them with the wood chips. I also like the green manure idea. So I will also give that a go in the rest of the garden to try to limit the buttercup spread!
    Thank you so much!
     
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  7. Ron B

    Ron B Paragon of Plants 10 Years

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    My original plan was to try to mimic nature

    The normal circumstance in nature is soil with organic debris falling on top, being integrated at the soil and debris interface - clear away what you have put down so far and fill most of the space with topsoil, plant in that. Then put organic debris on top, to function as mulch. And do not disturb the soil below the asphalt level because particularly if the paving occurred before 1980 the mixture used had a likelihood of being absolutely loaded with asbestos.
     
    Last edited: Feb 15, 2021

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