Soil depth

[emmagleb]

Hi, what would the minimum soil depth be for a small tree? Trying to add a roof terreace to a design project at uni and can't find the info anywhere. Alternativly, a massive pot can be used as a feature with the tree in it, but I'd prefer the tree to be planted properly. The structure designs have been reinforced to allow for the extra soil and groundwater weight, so all I need now is a depth.... Thanks :-)

[lafrancaise]

It all depends on the tree you want to plant. Some trees form roots on the surface, others go further down. Most trees will adapt to the situation they're in and their roots will grow to get as much water and food as possible. Citrus trees grow in little soil hence why we can plant them in pots.

Not much help with what you're looking for but somebody else might have an idea

[alan30]

There is a RHS book which may be of help?

Gardens in the Sky
Michele Osborne - ISBN 1903141206

I think you need to define small tree and what future management will be. If the tree is to be kept small then maybe 450mm will be OK; many trees confine the fibrous roots (water and feeding) to the top 600mm of soil but in many cases 600mm is not available and trees grow in virtually nothing over rock or scree. You need to consider soil volume; shalllower soil needs wider area for roots. You will need to consider how the tree is to be stabilised; overhead guying detracts from aesthetics, underground guying on roof garden may require you to increase depth of soil to accomodate guy system. You say weight including water has been calculated; where will the water drain as you do not want a waterlogged tree? Sure you have considered these issues but just typing as I think. I have seen trees planted in 300mm topsoil over compacted clay sub soil on reclamation sites and as the trees grew they just slid or peeled off the compacted clay; no stability as roots unable to penetrate clay.