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Planting on Hardcore

LoxleyLoxley Posts: 5,224
edited March 2019 in Plants
Hi all, I was wondering if anyone has had any luck growing stuff over a base of hardcore. A site I'm working on has about a 3m depth of 'Type 2' road stone. Our plan was to remove about 1.2m of the stuff, and replace with 900mm depth of imported subsoil and 300 of topsoil.

Unsurprisingly the contractor is spitting his dummy out about it, and I was wondering if we could get away with less... potentially much less. 

The planting is mainly perennials and ornamental grasses, with yew hedges and specimen Amelanchier. I am wondering if we went to 300mm of subsoil and 300mm of topsoil, it would be adequate for the perennials, grasses and yew? I am tempted to change the Amelanchier for something which is suitable for dry chalky soil - which is effectively what the hardcore is. Judas tree perhaps?


  • MarlorenaMarlorena Posts: 7,833
    300mm of topsoil alone, above hardcore, would be a luxury for some of my plants... I've planted a mixed border over hardcore with much less.... however I would have to do without the Yew hedges and tree... sticking with grasses and perennials is the way to go...   if you want height use Stipa gigantea.. as a centrepiece...
    East Anglia, England
  • MarlorenaMarlorena Posts: 7,833
    ..part of a 50 foot long mixed border over hardcore, rubble and builders sand, as that was all I had... it took me half an hour to plant a simple Aubrietia in this.. every plant involved removing some hardcore and adding some compost.. over several years it's become more fertile so I even have roses now... but the time and effort I've put into this border ..well, few people would have bothered if I'm honest... if you knew what was underneath... so don't give up on that one... but no trees !... no hedges !... no soil for those...

    East Anglia, England
  • LoxleyLoxley Posts: 5,224
    Thanks Marlorena, that border looks terrific!
  • raisingirlraisingirl Posts: 6,638
    Not quite the same, but there's a part of my garden which has maybe 300mm good soil with the remains of a very old farm trackway under it - i.e. cobble stones and hard core and all sort of old rubbish the farmer chucked down when it got muddy. I have holly, elder and buddleia all growing in it quite happily. There's also lonicera nitida absolutely thriving in there and lots of perennials, like geranium, Hesperantha coccinea and assorted ornamental grasses
    “Light thinks it travels faster than anything but it is wrong. No matter how fast light travels, it finds the darkness has always got there first” 
  • MarlorenaMarlorena Posts: 7,833
    @WillDB   thank you.. like raisingirl says, amazing what you can grow in it... I really enjoy my dry border now because it has the most perfect drainage imaginable.. doesn't matter how much it rains, and this means I can grow stuff in that border that demands perfect winter drainage, that wouldn't survive in normal conditions...  so it does have a lot going for it, over time.. 
    East Anglia, England
  • nutcutletnutcutlet Posts: 27,145
    My garden was a local tip for years before we came here. Plants do OK on hardcore, less well on carpet and plastic fertiliser sacks

    In the sticks near Peterborough
  • LoxleyLoxley Posts: 5,224
    Great, I feel a bit more confident in reducing the topsoil/subsoil layer. As luck would have it we have to lay 600mm of fresh soil in any case due to lead levels in the hardcore.
  • MarlorenaMarlorena Posts: 7,833
    House bricks and breeze blocks are not a lot of use either... I've dug up enough to build a new home..
    East Anglia, England
  • edhelkaedhelka Posts: 2,307
    I have sandy and stony soil, I only have approx. spade deep of good soil and then it's this stuff. It compacts almost like hardcore and the deeper I dig, the harder it is and the bigger stones are. To dig a hole for a rose or a small tree takes a good hour with a pickaxe.
    It still works well. Most plants don't need more than 30cm of usable soil. For plants that need it, you can always dig deeper, it will be hard work but possible.
  • LoxleyLoxley Posts: 5,224
    In the end the subsoil layer was reduced to 300mm, deepening to 600mm where trees were planted. The subsoil used was sandy clay (against my protestations - I was overruled).  300mm of good quality topsoil was laid over the top. 

    All looks good now, but some areas aren't draining well in wet weather. I should have put my foot down and insisted on more free draining subsoil. Concerned about those yews.

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