How to build a raised garden bed with Besser Blocks?

[DemiJosh]

  

 

I’m wanting to build raised garden bed around the perimeter of one of our fences as per attached photos. My question is in regards to draining and ensuring that the wall will have limited to no cracks in it once rendered. 

I feel it would be best to have the base area of the raised garden bed concreted prior to constructing the beds but then I’m unsure about drainage from the soil. Would you recommend only concreting the area in which the besser blocks would be laid on or can the whole base be concreted? 

Should the Besser blocks be filled with rocks/gravel when building up or a mixture of both concrete and gravel, is rebar needed in addition or only if the garden bed is built to a certain height? 

Thanks in advance! 

[MitchellMc]

Welcome to the Bunnings Workshop community @DemiJosh. It's terrific to have you join us, and many thanks for your question about building raised garden beds from Besser blocks.

Will the garden be constructed on all sides like the first image, or have the back be constructed from treated pine sleepers like the second image? 

Adding a concrete foundation under the walls would be a good idea to ensure they don't subside and shift over time. You could add the foundation under the walls or concrete over the entire area. If you are to concrete over the whole base of the garden bed, it's essential to add adequate drainage ports to the lower wall. These can be added to areas that can't be viewed, like the back of the garden bed. It's essential to add adequate drainage, or the area will fill up with water. Another option is to use an agi-pipe around the inside of the bed to remove excess water and drain it to a suitable location.

Before filling the garden bed, I'd recommend painting the rear side of the walls with Crommelin Exterior Grade Brushable Waterproofer. This will prevent excessive moisture from entering the blocks and saturating the wall. Doing so prevents staining to your white render and avoids it being pushed off the wall due to hydrostatic pressure.

Besser Block retaining walls are mortared together. The blocks need to be core-filled with grout and reinforced with steel for engineered and load-bearing walls. It's best to check with your local council to determine whether your wall requires engineering. If your garden beds are constructed with four sides and only a few courses high, then it's likely that they don't need to be engineered as they wouldn't be classified as a load-bearing wall.

Please let me know if you have any questions.

Mitchell

[DemiJosh]

Hi Mitchell, 

I hope to use besser blocks right round just to reduce any issues later down the track, but possibly a thinner block to reduce the space used. Only plan to construct the wall to just under or around 1m. Would you recommend steel reinforcements?

Generally how is AG pipe used? I’ve seen videos where a pipe goes to the top of the garden bed but I don’t understand the purpose or how this helps with drainage?

Would using rocks at the base and overflow pipes suffice or is landscaping fabric preferred? 

do you have any recommendations on drilling through the besser to install the drainage ports? 

[EricL]

Hi @DemiJosh 

Just to add to the recommendations made, I suggest having a look at this discussion - Advice needed to lay brick raised flower bed by @Brunnie_Rich. In the discussion you'll find excellent advice regarding building a foundation for a raised garden bed.

I tend to over engineer my projects just to make sure that they are fully supported. It would not hurt to put in steel reinforcements inside the block to give it a stronger profile should any lateral load come upon it. 

In regards to the agi-pipe, I suggest having a look at this discussion - Adding drainage to fix a muddy lawn, and returfing by @Ben. This is a very good example of using agi-pipe to divert water away into the drains. Using a combination of gravel and landscaping fabric will prevent the soil from flowing into the agi-pipe.

If you are drilling into the Besser Blocks, just make sure to check that the hole saw blade is rated for use on masonry. 

Please make sure to wear personal protection such as gloves, goggles and a dust mask when working on your raised garden bed.

If you need further assistance, please let us know.

Eric