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How to fill a raised garden bed

Kind of a Big Deal

Difficulty: Beginner

A raised garden bed can help make growing your own fresh vegetables and herbs a breeze. No deep digging, bending or kneeling is required because they’re above ground and can be built to a height that suits you. They can even be placed on a paved courtyard.


Building a raised garden bed is a terrific D.I.Y. project or you can buy flat-pack kits or pre-assembled boxes. The traditional box positioned directly on the ground is the best option but if you don’t have the space, there are orchard crates and boxes with solid bases available.  Just check there are plenty of drainage holes and elevate it on bricks or similar so it will drain freely. Remember that once filled it will be too heavy to move.


Once installed, follow our step-by-step guide to how to fill your raised bed.


Step 1

You might need to do some preparation work before you start filling the raised bed. For example, it’s wise to ensure any grass underneath the bed is dead and removed before you start filling it. And you should also ensure the base is level.


Depending on the eventual height and depth of the box, you might find it easier to start filling it before it is fully assembled. Shovelling aggregate and soil over a low wall takes less effort and is safer than filling a high bed.


1. Ensure any grass is dead and removed.jpg

Step 2

Add a layer about 80-100mm deep of aggregate / blue metal, crushed brick, broken concrete, polystyrene or similar to the base of the box to help excess water drain away. This is especially important in boxes with solid bases.


Cover the drainage layer with a layer of weedmat or geofabric which will allow water through but not soil or potting mix particles. This fabric layer is optional for boxes built on soil where drainage water doesn’t need to be clean because it soaks straight into the ground beneath.


2. Add a drainage layer.jpg  2.1 Screenings.jpg  2.2 Weedmat.jpg

Step 3

Deep boxes are perfect for those who can’t garden at ground or low levels, but can be very costly to fill completely with quality potting mix. Use ordinary garden soil to fill the box to about 400mm from the top.


If your overall height or depth of the box is less than 400mm, you can proceed directly to Step 4 and use potting mix.


3. Use oil to fill about 400mm from the top.jpg

Step 4

Time to add some premium potting mix. You’ll want to a minimum depth of 300mm of potting mix. Most vegies and herbs will grow and produce well if they have around a 300mm depth of potting mix, even root crops like carrots. Allow 50-100mm space on top for mulch.

Use the best available quality potting mix formulated for vegetables and herbs in your vegie box for optimal results, not garden soil which will dry out and compact quickly. Choose from 100% natural, certified organic, premium boosted with organics or premium with controlled release fertiliser.


Potting mixes tend to come in 25L and 50L bags. To determine the number of bags needed, calculate the volume required. For example, a bed measuring 1.5m wide x 2m long x 0.3m depth of potting mix will need 0.9 cubic metres, which is 900 litres (1000 litres is 1 cubic metre).


4. Use premium potting mix.jpg

Step 5

Don’t press the potting mix down but water it thoroughly so it will settle naturally. Top up again to within 100mm of the top if required.


Now add a 100mm layer of sugarcane, pea straw or Lucerne mulch over the surface to keep it moist and cool. The mulch will also help prevent water running off the top of the garden bed.


5. Pea straw for mulch.jpg

Step 6

Plant your seeds or seedlings and enjoy your harvests in the coming months.


6. Plant your seedlings.jpg


  • Raised garden bed
  • Aggregate / blue metal screenings, broken bricks / broken concrete (20-30mm in size) or crushed polystyrene boxes
  • Weedmat
  • Soil (for boxes over 400mm high)
  • Premium vegetable and herb potting mix
  • Organic weedicide (for boxes installed on the ground)


  • Gardening gloves
  • Face mask
  • Wheelbarrow
  • Shovel or spade
  • Hose 


1. Ensure any grass is dead and removed.jpg

2. Add a drainage layer.jpg

2.1 Screenings.jpg

2.2 Weedmat.jpg

3. Use oil to fill about 400mm from the top.jpg

4. Use premium potting mix.jpg

5. Pea straw for mulch.jpg

6. Plant your seedlings.jpg

12 Replies
Making a Splash

great  tips...nice work. 

Building a Reputation


   This is a great idea other than the polystyrene boxes as base filler (unless its the new corn based diodegradable polystyrene). Polystyrene will never break down, is highly hazardous if eaten by animals and contains lots of harmful chemicals that are used to originally make it . Do you really want to put something like that near your edible plants or into your soil to leach chemicals slowly into your groundwater/nearby waterways? 

I great alternative is used cork from bottles or shreded brown cardboard.

Kind of a Big Deal

Hi @Nellstar 


Polystyrene has been used in horticulture for many decades in growing and potting media to lighten the mixes and to improve drainage. It is preferred over perlite and vermiculite.  It is also used in commercial horticulture/agriculture for the packing of crops for transport from market gardens and orchards to markets and eventually to greengrocers.  It is quite stable and does not give off "harmful chemicals" when used and handled appropriately. It is safe to use around edibles.


In a raised vegie garden, where it is buried beneath the top 45 - 60cm of growing media, polystyrene is used as filler in the base of a deep box to improve drainage and to occupy space, to cut down on the overall volume of growing media required to fill the box.  It sits below the root zone.


It is cheap - greengrocers are often more than happy to give boxes to you to cut down the expense of disposal.  It isn't exposed to animals or wildlife so there's no danger of them eating it, and it doesn't break down to leach chemicals in underground water. It will compact over time but that's OK because fresh growing mix should be added to the top of the box every few years to maintain the depth.


So overall polystyrene is safe and practical to use in raised vegetable and herb beds and will not leach chemicals into the subsoil or groundwater.


Ordinary garden soil as filler compacts and doesn't drain well

Building a Reputation

@Noelle  Thanks for the feedback, ill do some more research into it. Its hard to distinquish between real or fake facts on websites nowadays.

Just Starting Out

I have four raised garden beds. These were difficult and costly to fill with soil/potting mix. So I opted for what waste I had on hand Eg. Bits of styrene, cardboard, scrunched up news paper and old potting mix. These were placed right at the very bottom and also acted as good drainage. Then I topped them up with garden soil, Cheaper type potting mix and cow manure all mixed in together. This seemed to work well as I have been growing herbs, plus home seeded tiny toms, (Tiny yellow egg toms from punnet)  lettuce and bock Choy.  These should do better now it’s warmer. Tried snow peas in planter pots these were too shallow, started off well but died (weather became too cold). Will now plant more seedlings with warmer weather. 

Bunnings Team Member
Bunnings Team Member

Welcome to the Bunnings Workshop community @MaryEvans. It's great to have you join us and many thanks for contributing to the discussion.


It's fantastic to hear about what has worked with your garden and how you managed to fill a large bed for a minimal cost. I'm a fan of bulking out my garden beds with Richgro 25L All Purpose Garden Soil Mix and Richgro 25L All Purpose Organic Compost. I'll then mix some Fine Farms 25L Blended Cow Manure through them to add a bit more organic material. I'll finish the bed off with the last 25cm of fill being a premium variety mix like Scotts Osmocote 25L Garden Soil Premium Planting Mix. The last bed I filled took close to 35 bags of 25-litre mix, so I certainly couldn't afford to do that all with a premium variety.


We look forward to hearing more about the projects you have going on around your house and garden and would encourage you to let us know if you ever need assistance or would like to share them with the community. I trust you'll find loads of inspiration within the community as our creative members are contributing their ideas here all the time.




Growing in Experience

Thank you all for the tips on filling raised garden beds, especially the tip about aggregate for drainage,  economical potting mixes and compost additives.


Have taken note for the planter boxes I plan to build.  😎👍

Bunnings Team Member
Bunnings Team Member

Welcome to the Bunnings Workshop community @Ange71. It's fabulous to have you join us and many thanks for jumping into the conversation.


It would be terrific to hear more about your own raised garden bed project. We'd encourage you to let us know if you need any help along the way or if you'd like to share your results with us. I trust you'll find loads of inspiration within the community as our creative members are contributing their projects here all the time.


You might also like to check out our Top 10 most popular raised garden bed projects for some more great ideas.




Finding My Feet

I've built a small raised bed using a low Birdies bed. I'm not very handy with wood, but okay with screwing nuts and bolts. As for filling, I took advice from Self Sufficient Me (Youtuber from QLD who has lots of these and grows heaps), but scaled down to my small garden:

Small raised bed, on old soaked cardboard (kill the grass and weeds). 

75% filled with dead branches and leaves (it sinks down). 

Stack (8x 25L) of ordinary garden soil (there are some good quality organic ones in packs at the hardware store)

Organic compost (3-4x 25L); Half a packet of cow manure and quarter packet fowl manure - these are all mixed up on top of the ordinary soil. This should come to the top of the small bed I built, but it sinks down. 

Good scattering of blood and bone, hosed in. Sugar cane mulch to above the rim. Wet down. Let the bed rest for a week before planting. 


Bunnings Team Member
Bunnings Team Member

That sounds like a fantastic method of filling a raised garden bed @NatalieM. Do you have any pictures of what you are currently growing in it? I'm sure our members would love to see your progress.




Just Starting Out

I am very new to raised garden beds for vegetables can you use rocks for the first layer instead of the other suggestions.


Bunnings Team Member
Bunnings Team Member

Hello @tezzat 


Welcome to the Bunnings Workshop community. It's fantastic to have you join us.


As mentioned in the guide, gravel is actually used at the bottom of the garden bed. However, you need to take into consideration the height of your raised garden bed. If it is low, I don't recommend using rocks as this will take away valuable space for root growth. But if you have a high garden bed then using rocks will be ok. 


If you need further assistance, please let us know.




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