How to improve drainage in a raised garden bed?

[SusieM]

I have placed a 5m x 900mm x 720mm high Birdies raised garden onto my grass, lined it with weed matting, cardboard and organic matter, filled it with premium soil but it doesn’t seem to be draining water adequately. Can you suggest how I can fix this without removing the soil?

[MitchellMc]

Welcome to the Bunnings Workshop community @SusieM. It's brilliant to have you join us, and many thanks for your question about drainage in a raised garden bed.

When you say that the bed isn't draining water adequately, what exactly is happening? Typically, with each watering, you'd only be putting on around one hundred litres of water at the very most, which should easily dissipate amongst the 950 litres of garden bed soil. The water shouldn't even reach the bottom of the bed, let alone have issues draining out.
 

I've had an issue with my garden bed as I used solid builders' plastic and forgot to poke holes in it. After torrential rainfall, it started to create a pond. Do you have quite clay-ridden soil in your location? Could it be that the ground is not letting to water dissipate? Alternatively, did you pack the cardboard so tight that it restricted the water from flowing out the bottom?

You might like to pick up a steel fence post and a sledgehammer and pound the post down through the soil and past the cardboard. You will need to put a number of holes through the cardboard to create adequate drainage holes in the base.

I look forward to hearing more about the issue, and please let me know if you have any questions.

Mitchell

[SusieM]

Thanks Mitchell

i don’t think I packed the cardboard too tight but I do know that the soil is very clay y under the buffalo grass. I purchased a soil meter from Bunnings to check the moisture and I haven’t needed to water for over a week. We’ve had a lot of rain but it just doesn’t seem to dry out at all. I’ll see how it settles and I’ll take your advice about the steel post if it doesn’t improve 

[EricL]

Hello @SusieM

I totally agree with my colleague's recommendation. The only other thing that comes to mind is that the soil could have settled in too well. I suggest using a Saxon Hand Cultivator with Timber Handle to aerate the top of the garden to promote drainage. However, if the water is still not draining correctly, I propose using the steel fence post as initially suggested.

Please keep us updated with your progress, we look forward to seeing your garden up and running. 

Eric

[Noyade]

Hi @SusieM 

Could be an optical illusion. But the corrugated iron wall on the left looks to be severely bulging out with the weight of the soil?

I'm thinking Dam Busters.

[SusieM]

Thanks 

I will give that a try if all my planted seeds fail to germinate.

Thank you for this suggestion

Regards

Susie

[SusieM]

Hi Noyade

YES!! that is the other issue! I installed as per the instructions with all the lateral braces installed but it seems to me that more lateral support is needed. I contacted Birdies and asked the question "Will it be a problem going forward". They didn't answer that question so i don't know if I need to rectify it or will it be okay. What do you think? I really don't want to have to remove the soil because I have planted out the garden with my vegie seeds. Thanks for that observation!

Susie

[MitchellMc]

Hi @SusieM,

I've contacted Birdies and sent through your images. I'll let you know when I have a response regards the bowing.

Mitchell

[MitchellMc]

Hi Susie (@SusieM) 

I've spoken to the team at Birdies, and it appears that the high quality of your soil could be the issue here. The supplied bracing is designed to support the bed when it's filled with potting mix. Potting mix is typically a much lighter medium containing a large portion of bark and doesn't retain as much moisture. It's advised in the installation instructions that if heavy soil is to be used, additional bracing is required.

This bowing isn't something they've experienced before, and they are more than happy to send you out some additional bracing for the top section. I'll reach out via private message to get your details.

Mitchell

[SusieM]

Thanks Mitchell

i thought I had thoroughly read the instructions but I missed that about potting mix. 
I appreciate your help with this

Susie