What footing size for brick planter box?

[jtaylor]

Hello. I want to build a raised garden bed along the entire length of my back fence out of left over bricks from my build. The garden bed will be half 400 high and half 500 high from FFL. I'm looking for advice about the footing required and drainage. My block is in Perth so it is all sand.

A - in regards to drainage is it acceptable to leave the centre of the garden bed 'hollow' so water can naturally drain away or so I need to put a layer of crushed rock or a plastic drainage product in the bottom of the garden bed?

B - I have seen videos of small non load bearing footing constructions built by laying a row of bricks perpendicular to the brick wall with 1 inch or so spacing between them. Concrete is then poured around and in between the bricks, trench mesh laid ontop  and pushed into the concrete forming a footing. Is this acceptable or do I need to pour the entire footing out of concrete with mesh?

[JacobZ]

Hi @jtaylor,

Thank you for your question and welcome to the Bunnings Workshop community, it is fantastic to have you with us.

Just to clarify, are you talking about clay bricks like these?

At the height of your garden beds, there aren't exactly stringent rules for footings. Some bricklayers will simply lay on top of compacted road base, with a bed of mortar on top, followed by the bricks; however, I think your plan to have a concrete footing is much better long term.

I'd suggest you start by digging out a trench around 300mm wide and adding a layer of road base, 50-100mm thick and compacting it with a tamper.

On top of this, if you are looking to reduce concrete costs, you could lay your bricks, then form around them with concrete, adding Jack 1800 x 200mm Light Duty Reinforcing Trench Mesh to strengthen the concrete. Ultimately, a full concrete footing would be stronger, but it will cost more in terms of materials.

You could then lay your bricks on top of your concrete footing.

There is no need to make any alterations to the base of the garden bed. Having natural soil will be ideal because it will allow for drainage as well as allowing the roots to grow deeper into the ground.

Let me know what you think and if you have any further questions, please don't hesitate to ask.

Jacob