How to reinforce a raised garden bed along a retaining wall?

[Aroon]

Hi,
I'm looking for advice on reinforcing galvanized metal garden beds, which I plan to install along the fence in my backyard. The garden bed dimensions are (4800 * 800 * 800) mm and (2400 * 800 * 800) mm. The garden beds do not have a bottom plate. The garden beds come with manufacturer provided internal metal bracings every 800 mm.

My backyard slopes 200 mm over 5.6m in one direction and 200 mm over 4m in another direction. I'm planning to excavate and fill no more than 100 mm to keep my garden bed level in both directions. I'm also planning to install an agi-pipe along the back wall of the garden bed; in line with the existing graded slope below the levelled surface. I will get a plumber's help to connect this new agi-pipe it to the existing storm water drain in front of the garden bed. The other agi-pipe from the backyard's retaining wall is connected at around 300 mm from the top of the storm water drain.

This is a 10 year old property and I do not see any visible damages on the retaining wall or fence. I would like to prevent the garden bed from collapsing on to the fence. Could you please advise:

a) The gap to be provided between the fence and the garden bed.

b) Should I install wooden fence posts around the garden bed; or other better alternatives to secure it in place.

c) What is the ideal height of the soil/garden mix/mulch fill inside the garden bed? A low profile deck is planned in the future, hence choosing a garden bed with profile height 800 mm to keep it elevated above the deck. If the garden bed's profile height is an issue for stability, I will look for other options to keep it shorter or level with the deck.

d) Is an agi-pipe required for the garden bed ? More information on this earlier in this post.

 layout

[EricL]

Hello @Aroon 

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your raised garden bed.

Please allow me to try and answer some of your questions.

• I propose a gap of 1 metre between your garden bed and the fence. This will allow you full access to all the sides of the garden bed and it will also let you to clean and mow the gap easily.
   
• If you feel that the metal bracings are not going to last long term, then adding timber support posts is the next practical next step. I propose using 200 x 50mm Sleeper H4 Sienna MicroPro 2.4m to support your garden bed.
   
• A raised garden bed height of 800mm is not overly high and is typical of most raised garden beds. In regards to filling the garden bed, I suggest having a look at these guides - How to fill a raised garden bed by @Noelle and the How to build a raised garden bed by @Adam_W. I also recommend looking at this featured discussion -  Hugelkultur raised garden bed using Colorbond fencing by @Aussie-Garden.
   
• I also suggest looking at these guides in regards to soil - How to choose the right soil for your plants by @Noelle and How to determine soil health by @Noelle.
   
• For larger beds such as yours, I suggest installing agi-pipe to properly divert the water away.

Let me call on our experienced members @Adam_W and @AlanM52 for their recommendations.

If you need further assistance, please let us know.

Eric

[AlanM52]

Hi @Aroon,

As per @EricL's suggestions and you could also do a timber in-fill with lift out sections between the back of the garden bed and fence for pot plants and/or garden ornaments and water feature in the corner.

Cheers

[Aroon]

Thank you @EricL  and @AlanM52 . Appreciate your response. I will update this thread once I've completed this minor project.