How to build a garden bed along the fence?

[bipul]

Hey team,

First post. I just need advice/guidance/suggestions on building a garden bed along the fence. I have very basic knowledge.

I have attached a photo and a sketch to clarify what I want to know:

• The length along the fence is 15m, and the width is 900mm.
• I plan to use 200 x 50mm Rad H4 Treated Retaining Timber sleepers and 88 x 21mm Radiata Merch Decking Griptread on top (lying flat).
• I’m considering building planters at either end of the bed (along the 15m side).

I need advice on:

• What size posts do I need? I’m considering 75 x 50mm F2 H4 Rough Sawn Treated Timber.
• How deep do the posts need to go into the ground for proper support?
• Do I need to add timber along the fence side (you should be able to see on the pictures), as there seems to be a gap between the ground and the bottom of the fence? If yes, what do you suggest?

Any suggestions would be helpful.

Thank you,
Bipul

 

[MitchellMc]

Welcome to the Bunnings Workshop community @bipul. It's sensational to have you join us, and many thanks for your question about creating a garden bed.
 

I don’t see where you mention how high the garden bed and planters will be. The height will determine what size posts you'll need. If the bed is only one sleeper high, your proposed 75 x 50mm posts should be fine. However, if you're going higher, I'd recommend using 100 x 100mm H4-treated posts for better support. Post depth, once again, depends on the height. Typically you'd create footer 300 x 300 x 450mm deep. 

You'll also need to add sleepers along the back of the bed to prevent soil from escaping and to keep it off the fence. Fence palings are typically only H3 treated, meaning they’re not designed for direct contact with soil and could decay over time.

Here's a helpful guide: How to build a raised garden bed.

Please let me know if you have any questions.

Mitchell
 

[bipul]

Thanks for the prompt reply, Mitchell.

Yes, you got it (sorry, I forgot to mention)—the height refers to just the sleeper height. The planter on either side would be two sleepers high (400 x 50mm).

Does the sleeper at the back of the bed need to be the same as the front one, or can I use a slightly thinner one? If yes, do you have any suggestions?

Is there a recommended distance for digging the posts? For example, for a 3m-long sleeper, would 3 or 4 posts (including the corner ones) be sufficient? What would the ideal number of posts for 15m be? 

Thank you for the link on how to build a raised garden bed.

I’ll keep the community posted on how it goes.

Thanks!

[EricL]

Hello @bipul 

Does the sleeper at the back of the bed need to be the same as the front one, or can I use a slightly thinner one? It has to be the same thickness all around so that the garden bed will be uniformly strong all around. You can't have sections that are weaker than the others.

In regards to the post, just keep in mind that the ends will need post, and a center post will be necessary to prevent the sleeper from bowing. For example, a 2.4m long sleeper will have a post at each end and one in the center at 1.2m. The same rules applies even if it is 3 meters long a center post must be put in the middle to prevent bowing. Keep in mind that if you are doing a garden bed15m long a post must be placed where the sleepers join together to keep structural integrity.

I propose drawing your plan on paper so that you will know exactly where your post will be needed. 

If you need further assistance, please let us know

Eric