I have a garden that is not completely flat that I am planing to level and could use some advice please.

The image below shows the layout of the garden currently. If I look out from the house at the garden, the first section is flat, but then between the end of the garage and the fence, is a drop of about 12-18 inches. This slope is just a bit too steep to be enjoyed. The brown lines are the fence.

enter image description here

My plan is to sink an additional 2 fence posts (75x75mm) between each pair of exiting fence posts (at least 4ft deep) and then use some fence boards to act as a brace to support the additional topsoil needed to raise the garden to be all level.

The image below shows a top down view of the current fence structure (in brown), where the boards are facing out of my property (so I have the 'ugly' side facing into the garden). The blue posts/boards are what I intend to do. The horizontal boards would be sunk about 4 inches below the current ground level, and would go to about 4 inches above the desired ground level.

High quality drawing is roughly to scale based on the size of a standard single garage

My question is;

Will the additional posts and wooden fence boards be strong enough to support the weight of the additional topsoil required raise the garden 12-18 inches?

Are there any other requirements that I need to consider? I assume that I will need to use some treated wood to ensure that the buried wood doesn't simply rot in the wet soil.

Any other general advice/tips are also welcome.

Thank You

Additional Information

  • At the end of the slope, on the other side of the fence is a side path and then our neighbors property.
  • To the left of the sloped grass is another neighbor, where our garden slopes down towards our northern neighbor, our left neighbors garden has a gentle slope down towards my garden.
  • The red box on the right of the garden image is the legal boundary of our property. To the right of that is the pavement. For some reason, the builders did not put the fence on the boundary line, but rather chose to put some lovely plants on my land (that I have to maintain). There is a slight slope down to the pavement (under 6 inches). Once I have permission to move the fence out to the boundary, there will need to be some further leveling that I would do using the same principal.

Final Comments

Thanks to the commenters below. I have taken the advice on board and concluded that Wood will not be sufficient. I will instead build a proper retaining wall with concrete foundations.

Thanks again

  • 1
    Will wood be strong enough to support soil? In word, no. It rots when in contact with moisture. You need to use cement interlock – kevinsky Apr 10 '18 at 18:35
  • 1
    In my experience, there has never been a way to use the fence to support soil. Nor any regulations that would allow this to take place between properties. Are you trying to cram everything up against the fence in an effort to...make a bigger lawn? No need to use a fence to hold soil up higher. Doesn't work work more than a year and then the fence needs to be completely replaced. – stormy Apr 11 '18 at 6:00
  • Magic, topography is priceless. Flat is boring and obviously you'll have drainage issues. What are the regulations about water off your property affecting your neighbor's? What are your permeable surface percentage restrictions? – stormy Apr 11 '18 at 6:03

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