Garden soil or Potting mix for large planter boxes?

[NamedUser]

Hello,

I have 2 planter boxes which are each 3m long, 75cm wide and 45cm deep. 

Would it be better to use garden soil or potting mix to in the boxes? I will planting heliconias and cascade palms. I will have 5cm of drainage stone on the bottom, followed by a layer of geofabric, and then the soil / potting mix. 

I read heliconias can run of risk of getting root rot, so would potting mix be the better option?

Thanks

[MitchellMc]

Hi @NamedUser,

For planter boxes like yours, potting mix is generally the better choice over garden soil. Potting mix is designed to be lighter, looser, and better draining, which helps prevent the roots of heliconias and cascade palms from sitting in water and developing root rot. Garden soil, on the other hand, tends to compact when placed in a container, which can restrict airflow around the roots and hold too much moisture. 

Filling such large boxes entirely with premium potting mix can be costly, so a practical approach is to layer the soil. You could use a more affordable garden soil or compost blend in the lower two-thirds of the box, then top it with a good-quality potting mix for the upper third where most of the roots will grow. This way, you balance cost-effectiveness with good drainage and plant health. Make sure your planter boxes have plenty of drainage holes and avoid letting water sit in the base, and consider adding a slow-release fertiliser to keep your plants thriving. 

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

Please let me know if you have any questions.

Mitchell

[NamedUser]

Thanks @MitchellMc 

Really appreciate all your help so far!

[NamedUser]

Hey @MitchellMc 

If I were to use https://www.bunnings.com.au/seasol-25l-advanced-potting-mix_p0274160 as the potting mix, would I still need to add a slow release fertiliser when planting, or would the Seasol potting mix already contain enough food? 

Thanks

[MitchellMc]

That mix contains slow-release nutrients designed to feed for up to six months @NamedUser. So, no need to feed in the immediate future.

Mitchell

[NamedUser]

Thanks @MitchellMc 

A bit late, but just sharing how the planter boxs are currently looking. Now just hoping the heliconias grow nice and big and start over taking the cascade palms. I have started to give them some Powerfeed every 7 days - will stop that in Autumn

 

[EricL]

Hi @NamedUser 

The plants look fantastic! Thank you very much for the update.

Eric