Impact of lowering soil level on existing trees
ruthmwhittington
Posts: 1
hi, our garden in SE London we are trying to turn from concrete central into a family-friendly garden with lawn, flowers, veg. A huge water feature and pond my husband has almost removed and we are left with a really high bank - 2 or 3 feet above the rest of the garden closest to the house. There are some lovely and established trees planted in the higher bank - we would like to lower the level of the soil in this area so there is more room for lawn etc., but don't to lose the treEs. We think the trees are a bay, chamelia, ornamental pear and two or three others we've not identified. If anyone has any advice they can share about how to lower the soil level without damaging the trees we would be very grateful. We have 5 months before the birth of our second bab to get the garden sorted (we've been here four years and have only got so far as to sort the patio and break up some of the concrete so daren't put things off any longer)!! Advice gratefully received. Ruth
Last edited: 14 May 2016 12:56:14
Posts
Photographs would help, to show the area you want to remove. In general terms, removing soil at one side isn't advisable as it could destabilise the trees if they are large.
Tree roots go outwards as well as down so any attempt to reduce the soil below the current level will create an issue with exposing the roots which may be just below the surface (ie, one or two feet down). If you expose them you would then probably want to cut them off, and then you risk the tree no longer being anchored with the risk of it toppling over especially in a high wind or even strong breeze. On a mature tree, the roots dispersal can be as wide at the canopy, however, it will depend on the tree. As a good guide you can do a root:trunk ratio of 12:1. So for every 1 inch of trunk diameter, the roots go out by 12 inches. So if the diameter of the trunk is 20 inches, you're looking at around 240 inches or 20 foot. I don't see how you can feasibly reduce the level of the ground a tree is already planted in without doing serious damage to the tree or killing it. You either need to leave them be, or make the difficult decision to remove them, lower the ground and replant with same or something different in the newly lowered ground.
They will die if you remove the soil and then keel over ! The Bay might survive if you dig enough root ball and re plant it , The camellia might move too , but it is a bit late in the year for it to move . The Pears will not . how about building a retaining wall round them ?