You don't need to fill the whole bed with premium garden soil
Deep raised garden beds can take a surprising amount of soil. A layered approach can reduce the amount of heavy soil you need, make use of organic garden materials and create a healthy growing environment for your plants.
Before You Start
Place your garden bed on firm, level ground and make sure it is completely assembled before filling.
If your garden bed includes braces, support bars or other structural fittings and always install them as directed before adding any material.
Fill the bed gradually and evenly, working around the bed rather than filling one end completely before the other.
A Simple Layering Method
1. Bottom Layer — Bulky Organic Material
For a deep garden bed, start with a layer of suitable bulky organic material such as:
- Small logs or sections of untreated timber
- Branches and twigs
- Dry leaves
- Plant trimmings
- Straw
This takes up some of the deeper space that would otherwise need to be filled with soil.
Important: Use untreated, natural timber
only. Avoid painted, treated or manufactured timber products.
2. Middle Layer — Organic Garden Material
Add a mixture of softer organic materials over the larger pieces.
Suitable materials can include:
- Leaves
- Grass clippings in thin layers
- Straw
- Aged plant material
- Partly broken-down compost
- Small amounts of aged manure
Water the layers lightly as you build them to help everything settle.
3. Growing Layer — Quality Soil & Compost
Finish with a generous layer of good-quality soil suitable for the plants you intend to grow.
A mixture of garden soil/topsoil and plant-based compost works well for many raised garden beds.
Aim to keep approximately 30–40 cm of quality growing medium at the top where most vegetable and herb roots will grow.
Don't Pack It Down Too Hard
There is no need to heavily compact each layer.
Place materials evenly, gently settle them and add your growing mix on top. Over time, organic materials naturally break down and the level of the bed may drop.
Simply top it up with additional soil or compost when required.
What About the Weight?
A deep garden bed filled entirely with dense, wet soil can become extremely heavy and apply pressure to the sides of the garden bed.
Using appropriate organic material in the lower section not only reduces the quantity of soil required, but also better manages the weight of the contents, ensuring your garden bed maintains it's structural integrity and will serve you for many years to come. However, your garden bed must still be correctly assembled and filled according to its intended design.
The contents of a raised bed also create outward pressure on the side panels, particularly after watering or heavy rain, so don't overfill the bed or ignore any braces or supports supplied with it.
Avoid Filling the Base With
- Large quantities of rocks or gravel simply to take up space
- Concrete or building rubble
- Treated or painted timber
- MDF, particleboard or plywood
- Plastics or household rubbish
- Diseased plant material
- Meat, dairy or pet waste
Rocks and gravel can actually add considerable weight rather than reducing it.
After Filling
Water the bed thoroughly and allow the contents to settle.
You may find the level drops during the first few weeks or months as air spaces disappear and organic material begins to break down. This is normal.
Top up with more quality soil or compost as required — then you're ready to plant.
Garden Co Tip
Save the best soil for the top of the bed. Your vegetables and herbs need good growing medium around their roots; they don't need expensive premium soil all the way to the bottom of a deep raised bed.
