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Raised planter under maple tree

Discussion in 'Landscape Architecture and Design' started by Woodland, Aug 14, 2006.

  1. Woodland

    Woodland LawnSite Member
    from Maine
    Messages: 207

    Looking for a little advice here. I'm going to be building a stone planter around a business sign for a client. The sign sits underneath a mature maple tree. The small bed that was around the old sign (only about 8" tall) was completely filled with roots from the tree, preventing anything from growing there. The new planter will be about 18". The planter is not right next to the tree but most of it is within the trees dripline. I am concerned about the tree roots invading the new planter as well and I'm looking for some advice about how to prevent this. Some thoughts that we've thrown around include a layer of crushed stone covered with weed fabric (Lumite Ground Cover), plywood (with drainage holes?), and nothing at all - the roots wont grow up that much as to fill the bed. Any thoughts on the success of these methods or other thoughts?
  2. mjohnson1

    mjohnson1 LawnSite Member
    Messages: 76

    if it's a silver maple you'll have those darn helicopoter seed things to deal with as well. i'm not sure if other maples do that we only have a silver maple in our yard. i'd be afraid a peice of plywood would rot even if it's pressure treated, being under dirt its gonna be constantly wet. the crushed stone idea sounds pretty good to me. is a thin (maybe 2") layer of concrete out of the question? maybe you could slope it slightly towards the sides and come up with a way to drain it, maybe leave a small gap between the stones at the bottom. you could put a peice of heavy gauge screen like hardware-cloth behind the gap to keep the soil from washing out. good luck
  3. Woodland

    Woodland LawnSite Member
    from Maine
    Messages: 207

    What, plywood rot? Amazing how the simplest things can slip your mind... It is a Norway maple. I like the idea of the hardware cloth. A couple of layers right on the ground to make the holes really small then covered with a thin layer of stone for drainage then weed cloth just might do the trick.
  4. Grn Mtn

    Grn Mtn LawnSite Senior Member
    Messages: 863

    your either going to kill the tree by smothering the roots with 18" of material, or the roots will continue to heave what is laid on top of them.

    not sure if this would work in your situation but if you must put something under the tree put it up above the ground like a deck of sorts, than put potted shade loving plants plants on the "deck". this way you'll only have to dig some post holes and the deck would allow water and air to still feed the root zone.
  5. sheshovel

    sheshovel LawnSite Fanatic
    Messages: 5,112

    I agree with Grn Mtn . I do not recommend adding soil over tree roots at all it can kill the tree. They do have a product called RootGuard that you can lay down to keep the roots from coming up , but like I said add ing soil over a tree's roots can and will eventually kill the tree.
  6. AGLA

    AGLA LawnSite Bronze Member
    Messages: 1,774

    A new method for keeping roots from going where they are unwanted is an air gap. You may have seen this in some nurseries where they heal in plants for long periods of time. They have almost a pot within a pot that keeps an air space between the inner pot and the material that they heal them into. You can use the same technique by having an air void between your planter and the ground below. You could scrounge some kind of steel grate and put a silt cloth over it, or some other material.
  7. Grn Mtn

    Grn Mtn LawnSite Senior Member
    Messages: 863

    I read this a little more carefully this time and see that your not doing something around the whole tree just around the sign. What is the size of this planter box? 2'x2', 3'x3', or 4'x4'? or is the sign not a pole but one spread between two posts?

    A local nursery here makes "trees" out of Petunias and a wire rack that holds like 30 pots, its really kind of cool. Maybe you could do something similar and than just mulch the ground underneath.
  8. Woodland

    Woodland LawnSite Member
    from Maine
    Messages: 207

    The sign is between two post approximately 7' apart. The planter is 7' wide along the axis of the posts and about 6' wide the opposite way. The closest that the planter is to the tree trunk is about 5'.

    I understand the concern about putting soil over the tree roots. Two points about that, one, the actual area under the tree that will be covered won't be that significant and two, it is a Norway maple that has plenty of roots in other places to support the tree! So, the trees health aside, the major concern is keeping the roots from invading the planter. Since the project is completed, here is what we did.

    We dug a trench about 4" - 6" deep as a foundation for the stones and laid 1/4" galv. hardware cloth in it then filled it with crushed stone. We then constructed the wall. Once it was up, we covered the inside of the planter bottom with several layers of the hardware cloth and then several inches of crushed stone. Over that we put a layer of weed fabric (mostly to keep the soil above from filtering into the stone layer) and then our soil mix.

    This seems to be an adequate solution. I am still somewhat concerned about heaving from root growth as someone mentioned but that can be dealt with down the line if necessary. I'm also intrigued about this root guard product, any other info? Also, have heard about the use of copper in repelling roots. When I heard about it, it was being used inside pots to prevent roots from reaching the edge of a pot and then circling. Not sure how well it would have worked in a situation like this, but I'm willing to bet that it would have been cost prohibitive anyway.
  9. Grn Mtn

    Grn Mtn LawnSite Senior Member
    Messages: 863

    I saw the copper impregnated landscape fabric at Lesco last year, not sure if they have it now.
  10. mdvaden

    mdvaden LawnSite Bronze Member
    Messages: 1,946

    If the 5' distance is accurate, then it's not as devastating to the tree as your first post might have connoted.

    Although not devastating, it's not beneficial to add soil over roots under a dripline.

    But, if you have to have the bed, and if it's mimimal for size, you may be able to add soil without killing the tree.

    You need to counteract what would do the damage. That includes trapping of carbon dioxide gas, since roots work backwards from leaves. Root use oxygen and release carbon dioxide.

    If you can lay some perforated pipe in a net work on top of the existing grade, and under the fill, add fine gravel over the perforated pipe, and vent it out in several places to allow wind and gases to pass in and out.

    Then you can lay that root gaurd or a root barrier fabric over the porous layer, and place your planting soil on top.

    That is similar to what's done for preservation of some large trees when a commercial building is developed.

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