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Planting above rainwater Soakaway


First post and I am pretty new to gardening so any help would be appreciated :)

We are having to have a new soakaway dug and to cut a long story short the easiest place to put one is in this circular bed in our front patio.

The current plant (I think its a castor oil or false castor oil plant?) will need to be removed. Our builder says anything with a shallow root system will be fine to plant on top…so any suggestions!?

Id like a large shrub/brush and for it to be a least 1m tall (pref around 1.5m tall) and flowering, it MUST have a shallow root system…I was thinking maybe a Hydrangea (if so suggestions on variety) but would welcome any other suggestions.

The bed is quite big…around 2.5m across and I'd like little or low maintenance if possible?

Thanks :) 


  • wild edgeswild edges The north west of south east WalesPosts: 7,556
    Are you using the Polypipe soakaway crates? Generally you have a good half metre of soil cover over those and if you raise the bed up lie you have currently then there should be plenty of depth for the roots of most plants.
    A great library has something in it to offend everybody.
  • JennyJJennyJ DoncasterPosts: 6,138
    How much of the day does it get sun for? rhododendrons have shallow root systems but don't like full sun all day (but I think the same is true of hydrangeas - prefer part shade).
  • TheVanguardTheVanguard Posts: 109
    Hi the area is north facing so is shaded by house for part of the day...

    i am not sure how deep it will be, I think he mentioned it will be covered in some kind of material....

    i wanted shallow roots roots to avoid any future problems...
  • DovefromaboveDovefromabove Central Norfolk UKPosts: 77,480
    If it’s a north facing bed have a look at the oakleaved hydrangeas. A larger plant and more elegant flowers than the more usual mopheads with the added bonus of great autumn colour from the foliage. 
    “I am not lost, for I know where I am. But however, where I am may be lost.” Winnie the Pooh

  • JennyJJennyJ DoncasterPosts: 6,138
    I think it's best to hold off on the final decision until the work is done and you know exactly how much soil depth you have.  It's not clear what your builder's definition of "shallow" is - if it turns out to be something like only 6 or 8 inches (15-20 cm) then a 1 to 1.5 m tall shrub is probably not going to work there.
  • TheVanguardTheVanguard Posts: 109
    I think he was taking a couple of meters down so I suspect there will be 50cm or so as a poster above suggested...

    I wanted shallow roots as I didn’t want to have a problem in 10/15 years time. 
  • JennyJJennyJ DoncasterPosts: 6,138
    Then you should be OK with anything that doesn't have a tap root.  I think I would still wait and see because in my experience what builders say and what they actually do don't always match up. 
  • matt_fendermatt_fender Posts: 165
    edited May 2019
    We had a soakaway put in as part of an extension build, right in the middle of the lawn. Even though the top is a good 50-75cm down, you can still see a brown outline of the shape (and connecting pipes) after a prolonged dry spell, so I guess either that ground is more prone to drying out or grass roots go surprisingly deep. I doubt any smaller plant like you describe is going to do too much damage though - these are strong plastic crates typically wrapped in a few layers of membrane - although I guess you wouldn't want to put a tree there.
    Also I wouldn't take advice on plants from any builder I have met, although you may have found an exception!!
  • AnniDAnniD Posts: 9,653
    For some reason, l'm picturing a large circular bed full of sedums and sempervivums. No idea if that would work ?

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