Raised garden bed soil composition and ratio

[Michael-T]

I am looking for some help with preparing the soil for my raised garden bed. The garden bed directly sits on my yard and is not boxed in from the bottom.

The dimension of the raised garden bed is as follows:

Length: 2.5 meters
Width: 80 cm
Height: 60 cm

This is 1.2 cubic meters which according to soil calculators is 1.8 tonnes of soil.

I believe I need to fill the garden bed with the following:

1. Organic soil
2. Organic garden mix
3. Compost
4. Green mulch
5. Zeolite
6. Perlite
7. Vermiculite
8. Seamungus

I need to get the products in 25-30 litre bags.

By my calculation and talking to some landscaping supplies, I need around 40-50 (25 liters each bag) bags to fill the bed.

The issue I am having is figuring out the ratio of the above 8 products I need to use.

Can anyone help me out?

Thanks.

[MitchellMc]

Hi @Michael-T,

That sounds like a pretty specific mix of ingredients for a garden bed. They are not all required, though likely have their own uses. You should find this guide useful: How to fill a raised garden bed. Our expert horticulturist @Noelle suggests soil and premium vegetable and herb potting mix.

If you did want to go with the formulae you've posted, I'd suggest the first three would be equal parts. You can add a proportion of green mulch, but it's not essential and used for bulking out the fill. For the Zeolite, Perlite and Vermiculite, you might like to add one or two bags of each.

1. Organic soil - 15 bags

2. Organic garden mix - 15 bags

3. Compost - 15 bags

4. Green mulch

5. Zeolite - 2 bags

6. Perlite - 2 bags

7. Vermiculite - 2 bags

8. Seamungus - As per instructions or five heaped handfuls to the top layer.

Please let me know if you have any questions.

Mitchell

[Michael-T]

@MitchellMc 

Thank you so much.

That sounds like a pretty specific mix of ingredients for a garden bed.

Because of the high amount of fill in the bed, I am trying to get the it right the first time. So to save me time and money in the long run.

Is it necessary to use garden soil in the garden bed? Or can I use garden mix instead of the garden soil?

Do I need to fill the garden bed by specific layers? Or all the ingredients can be mixed in?

[Noelle]

Hi @Michael-T 

If you use bagged organic soil, garden mix and compost, you probably do not need to add more than half to one bag each of the zeolite, perlite and vermiculite, if that, as these mixes are quite light, well aerated and porous in their own right and don't generally need the addition of further materials to improve their aeration or porosity. Too much of these materials may leave you with a mix that drains too well and doesn't retain enough moisture to sustain your crops.

I would tend to go with the bagged mixes, green mulch and half to one bag of zeolite and not worry about the perlite or vermiculite in a bed that's only 600mm in height.

[MitchellMc]

Hi @Michael-T,

It's great to see @Noelle has added to the discussion, and I would certainly recommend following her advice.

What "garden mix" had you seen that you'd like to substitute for the soil?

The ingredients should be mixed, and any premium mix used at the top where plants will establish.

Mitchell

[Michael-T]

@Noelle 

Thank you for your reply.

more than half to one bag each of the zeolite, perlite and vermiculite

So I should add 12KG of zeolite to 25L of garden soil?

I am having a hard time sourcing green mulch in Sydney. If you are in Sydney, do you know where I could buy some?

@MitchellMc 

What "garden mix" had you seen that you'd like to substitute for the soil?

Perhaps these garden mixes?

https://anlscape.com.au/landscaping/bagged-products/general-gardening-products/greenlife-garden-mix-...

https://www.bunnings.com.au/scotts-osmocote-25l-garden-soil-premium-planting-mix_p3010198

https://www.bunnings.com.au/garden-basics-25l-garden-soil-mix_p0274300

Does bunnings sell bagged organic soil? I could not find any in the website.

[Noelle]

Hi again @Michael-T 

No more than half to one bag of zeolite for the entire 1.2 cubic metres of the soil mix for the bed, not half to one bag of zeolite per 25L bag of mix/soil.  That would be overkill!

Have a look at https://www.bunnings.com.au/scotts-25l-performance-naturals-soil-improver_p0182066

This could be used in place of garden mix.

You may find green mulch either through your local council - often the green waste collected in kerbside recycle bins is mulched and sold back to residents.  Or you could look at ANL - anlscape.com.au