Planting depth for Dahlia and Tree Roots

Discussion in 'HortForum' started by Helen Leung, Apr 26, 2006.

  1. Helen Leung

    Helen Leung Active Member 10 Years

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    I want to plant some dahlias where there used to be a douglas fir tree. The neighbour has now removed the tree and I have full sun!! Yeah! The only problem is that the tree roots are the size of my fist in some areas!

    My question is: do I have to take out as much of the roots as possible and build a raise bed on top of it? Or could I just build the raised bed w/o digging? And how much soil should I get? 4"? 6"? Any suggestions?


  2. oscar

    oscar Active Member

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    Surrey, England
    Rough guide to top soil depths (minimum for successful cultivation, if memory serves)
    Grass 6" (150mm)
    Shrubs 18" (450mm)
    Trees 24" (600mm)
    Amazing what you remember from your student days....anyway i dont think we were given a depth guide for guess would be somewhere in between grass and shrub, say 12" 300mm (Dahlias maybe even less)
  3. Ron B

    Ron B Paragon of Plants 10 Years

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    WA USA (Z8)
    If you can get topsoil you think is good for dahlias and put that down, plant in that try that approach. Influence of conifer (maybe acidification, for instance, or water-repelling waxes) on condition of soil beneath it will still be present, probably not what dahilas would like to be subjected to.

    Search www for "dahlia cultivation" etc. for depth recommendations. I don't think it matters much, unless you want them deep enough for possible overwintering without lifting. Otherwise, I think you may find you will be told to plant the bigger-growing kinds deeper.

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