You've assembled your raised garden bed and found the perfect spot in the garden.
Now comes the next question:
What should you fill a raised garden bed with?
The simplest answer is to fill the entire bed with a good-quality raised garden bed mix from a reputable local landscape supplier.
But if you have a taller raised garden bed, filling the entire volume with premium soil can require a considerable amount of material.
There is another option.
By creating raised garden bed layers using suitable organic materials in the lower section and quality growing soil towards the top, you can reduce the amount of premium soil required while making use of materials you may already have around your garden.
In the video below, Michael from Birdies Garden Products demonstrates one practical way to fill a tall raised garden bed from the ground up.
The Simplest Way to Fill a Raised Garden Bed
Let's start with the easiest option.
You can simply fill your raised bed from bottom to top with a quality raised garden bed mix.
Your local landscape yard or garden supplier should be able to recommend a mix suitable for growing vegetables, herbs and flowers.
A good raised garden bed soil mix should provide a balance of:
- Good drainage
- Moisture retention
- Organic matter
- Nutrients
- A loose structure that allows roots to grow easily
For lower-profile raised beds, filling the entire bed with a quality growing mix is often the most straightforward approach.
For a tall raised garden bed, however, the volume can add up quickly. That's where layering can be useful.
Before ordering soil, use the Birdies Raised Bed Soil Calculator to estimate how much your particular bed requires.
Step 1: Consider What Is Underneath Your Raised Garden Bed
Before you start filling your raised garden bed, take a look at the surface underneath it. The best preparation depends on where the bed is being installed.
Installing a Raised Garden Bed Over Soil
If your Birdies bed is going directly onto existing soil, you may not need to do much preparation at all.
In the video, Michael's bed is positioned over an area with bark on the surface and soil underneath.
Leaving the bottom of the raised bed open allows the soil inside the bed to interact with the existing ground underneath.
Earthworms and other beneficial soil organisms may also move between the natural soil and your raised bed over time.
Step 2: Decide Whether You Need a Weed Barrier
If weeds are likely to grow through the bottom of the bed, you can create a biodegradable barrier before adding the other materials.
One of the easiest options is cardboard.
Another option in certain situations is geotextile fabric.
When Can Geotextile Fabric Be Useful?
Geotextile fabric may be useful where:
- Persistent weeds are a concern
- The bed is close to established trees
- Tree roots may grow towards the moist soil inside the bed
- The raised bed is being installed over a hard surface
- You want to reduce soil escaping from underneath the bed
Whatever material you use underneath your garden bed, make sure water can still drain freely. Good drainage is essential for healthy plant roots.
Raised Garden Bed Drainage: Why It Matters
Water needs to be able to move through and out of a raised garden bed.
Poor drainage can leave plant roots sitting in excessively wet soil, which can negatively affect plant health.
Your drainage requirements will depend partly on where the bed is installed.
A bed positioned over natural soil can generally drain down into the ground underneath.
A bed placed over concrete or another hard surface requires more consideration because water must be able to escape around the base.
Can You Put a Raised Garden Bed on Concrete?
Yes, a raised garden bed can be installed on a suitable concrete or other hard surface, but drainage becomes particularly important.
Unlike a bed sitting directly on soil, excess water cannot simply move down into the ground underneath.
Your raised bed therefore needs a clear way for water to escape.
Michael explains in the video that geotextile fabric can help prevent soil from washing out underneath a bed placed on concrete.
He also discusses using a shallow base layer of suitable coarse material when appropriate.
The important principle is to avoid creating a raised garden bed where water becomes trapped around the roots.
Step 3: Reuse Your Birdies Cardboard Packaging
One useful material may already be sitting next to your newly assembled garden bed.
The cardboard packaging.
In the video, Michael cuts up the cardboard the Birdies bed arrived in and lays it over the bottom of the bed.
Cardboard can help:
- Suppress weeds underneath the bed
- Create an initial biodegradable layer
- Add carbon-rich organic material
- Repurpose some of your garden bed packaging
Remove plastic tape, staples, labels or other non-compostable materials before putting cardboard into the garden.
The cardboard does not need to create a perfectly sealed floor.
Over time, it will become wet and naturally break down.
How to Fill a Tall Raised Garden Bed Using a Hügelkultur-Style Method
Tall raised garden beds provide several advantages, including easier access and substantial growing depth. They also hold a considerable volume.
Rather than filling every inch with premium soil, you can use a method inspired by Hügelkultur to fill part of the lower section of a tall bed.
Hügelkultur is a traditional European gardening technique based around layers of woody material and other organic matter.
For a tall raised garden bed, a simplified Hügelkultur-style approach can help occupy some of the deeper space before the upper growing layer is added.
The important distinction is that the organic material underneath does not replace your quality growing soil.
Your plants still need a generous upper layer of suitable raised garden bed mix.
Hügelkultur is particularly useful in drier parts of the country where the larger logs act like a sponge, retaining moisture and releasing this slowly as required.
Step 4: Start With Larger Woody Material
Begin the lower section of the bed with some of the largest clean organic material you have available.
Suitable materials may include:
- Untreated logs
- Larger branches
- Woody garden prunings
- Old untreated timber
- Other clean woody garden material
In the video, Michael uses pieces of old wood that were already available around the garden.
These larger materials occupy some of the deep volume in the bed and gradually break down over time.
What Wood Should You Avoid?
Avoid:
- Chemically treated timber
- Painted timber
- Stained or coated wood
- Diseased plant material
- Contaminated wood
- Synthetic materials
- Plastic
- Construction waste of unknown origin
Use clean organic materials that you are comfortable placing inside a food-producing garden.
Step 5: Add Smaller Branches and Woody Material
After adding the larger woody material, start filling the spaces with progressively smaller pieces.
Michael uses dry bamboo stakes as the next layer in the video.
Other suitable materials might include:
- Small branches
- Twigs
- Woody prunings
- Dry garden cuttings
- Bamboo
Think of the process as moving gradually from larger material at the bottom to finer material as you move upwards.
Step 6: Add Green Garden Waste
The next raised garden bed layer can include suitable green organic material.
In the video, Michael uses materials already available around the garden, including:
- Grass clippings
- Pulled garden plants
- Weeds
- Green garden waste
Other compostable garden materials may also be suitable.
Be selective about what goes into the bed.
Avoid diseased plants and persistent invasive weeds, particularly weeds carrying mature seeds.
It is also better to mix materials rather than creating one very thick, compacted layer of fresh grass clippings or other wet green material.
Step 7: Add Quality Raised Garden Bed Soil
Once the lower section has been filled with your organic layers, it is time to create the growing zone.
This is the most important section for your plants.
Michael finishes the bed with a quality raised garden bed mix purchased from his local landscape yard.
The upper layer should provide enough quality growing medium for your vegetables, herbs or flowers to establish healthy root systems.
Michael explains in the video that many common vegetables can grow successfully with around 12 inches of quality soil, although root depth varies depending on what you are growing.
The deeper organic layers help occupy space in a tall bed. They should not replace an adequate layer of quality growing soil.
What Are the Best Raised Garden Bed Layers?
If you're wondering how to layer a raised garden bed, there isn't one rigid formula every gardener must follow.
For a tall bed using the method demonstrated in the Birdies video, the layers might look something like this:
Quality raised garden bed soil
Green garden waste
Smaller branches, bamboo and dry woody material
Larger untreated logs and branches
Cardboard
Existing soil or prepared base
BOTTOMYou do not need to use every material shown here.
The right approach depends on:
- The height of your raised garden bed
- What you plan to grow
- The surface underneath the bed
- Your local climate
- Materials available around your garden
What Should You Put in the Bottom of a Raised Garden Bed?
For a raised bed positioned directly over soil, you may need very little at the bottom.
A layer of plain cardboard can help suppress weeds while breaking down naturally over time.
For a tall raised garden bed, larger untreated woody materials can then form part of the lower filling layers.
If the bed is installed over concrete or another hard surface, preparation may be different because maintaining drainage becomes particularly important.
There is no need to fill every raised garden bed with logs or organic waste.
For shorter beds, quality raised garden bed soil from bottom to top is usually the simpler option.
What Raised Garden Bed Soil Should You Use?
Your upper growing layer should contain a quality soil mix designed for raised garden beds or vegetable gardening.
Rather than simply using ordinary garden dirt, look for a balanced growing medium containing a combination of soil components and organic matter.
The exact formulation varies between suppliers and regions.
A reputable local landscape yard should be able to recommend an appropriate raised garden bed mix for your area.
Good raised garden bed soil should:
- Drain excess water effectively
- Hold enough moisture for plant roots
- Contain organic matter
- Remain loose enough for root development
- Provide an appropriate growing environment for vegetables and herbs
Avoid filling the entire bed with compost alone.
Compost can be useful as part of a balanced growing medium and for periodically enriching your soil, but it is generally not intended to function as the entire soil profile.
Raised Bed Soil vs Lower Filling Material
Think about a tall garden bed as having two different zones.
Lower Filling Zone
This may contain suitable:
- Logs
- Branches
- Cardboard
- Green waste
- Clean organic material
Upper Growing Zone
This should contain quality:
- Raised garden bed mix
- Vegetable garden soil
- Appropriate soil and organic matter
Your plants primarily depend on the growing zone.
Should You Fill a Raised Garden Bed Right to the Top?
Yes.
When setting up your Birdies raised garden bed, fill it to the intended soil level rather than deliberately leaving a large empty section at the top.
Materials inside a newly filled bed will settle over time.
This happens because:
- Soil settles after watering
- Air pockets disappear
- Organic material begins decomposing
- Woody material slowly breaks down
A garden bed that appears completely full when first filled may therefore sit lower after several months.
This is normal.
Simply top it up with additional quality soil or compost as required.
How Much Soil Do You Need for a Raised Garden Bed?
The amount required depends on the dimensions and configuration of your particular bed.
Factors include:
- Length
- Width
- Height
- Shape
- Configuration
- How much of the lower section is filled with organic material
Rather than estimating manually, use the Birdies Raised Bed Soil Calculator.
How to Fill a Raised Garden Bed Cheaply
One of the main benefits of the layering method shown in the video is that it can reduce the amount of purchased soil required for a tall garden bed.
Rather than paying for premium growing mix to occupy space far below the main root zone, you may be able to use suitable materials already available around your property.
These could include:
- Cardboard
- Untreated logs
- Pruned branches
- Bamboo
- Grass clippings
- Suitable garden waste
You still need to invest in a quality growing layer at the top.
The goal isn't to replace good soil with waste material. It's to use the deep volume of a tall raised garden bed more efficiently.
What About Shorter Raised Garden Beds?
The Hügelkultur-style method is most useful when you have substantial depth to work with.
For lower-profile raised beds, there is less benefit in filling valuable root space with large woody material.
Birdies 15-inch raised garden beds already provide a useful growing depth for many vegetables, herbs and flowers.
For these beds, filling the bed with a quality raised garden bed mix is generally the simpler approach.
Explore Birdies 15-Inch Raised Garden Beds
For gardeners who prefer additional height and growing volume: Explore Birdies 29-Inch Raised Garden Beds
Raised Garden Bed Filling FAQs
What Do You Fill a Raised Garden Bed With?
The simplest option is a quality raised garden bed mix from a reputable landscape or garden supplier.
For taller raised beds, you can also use suitable organic materials through part of the lower section before adding a generous upper layer of quality growing soil.
What Should You Put in the Bottom of a Raised Garden Bed?
If the bed is installed over soil, plain cardboard can help suppress weeds and break down naturally.
In taller beds, clean untreated logs, branches and other organic material can form part of the lower layers.
Can You Put Cardboard Under a Raised Garden Bed?
Yes.
Plain cardboard can be used as a biodegradable layer underneath a raised garden bed. Remove tape, staples, labels and other synthetic materials first.
Can You Fill the Bottom of a Raised Garden Bed With Logs?
Clean untreated logs can be used as part of a Hügelkultur-style filling method in taller raised garden beds.
Avoid treated, painted, coated or contaminated timber.
Can You Put Grass Clippings in a Raised Garden Bed?
Grass clippings can form part of the organic filling layers in a tall raised garden bed.
Mix them with other materials rather than creating one thick, compacted layer.
Avoid clippings from lawns recently treated with products you would not want inside a vegetable garden.
How Deep Should Soil Be in a Raised Garden Bed?
The ideal depth depends on the plants you want to grow.
Michael explains in the video that many vegetables can grow successfully in around 12 inches of good-quality growing medium.
Some plants have deeper root systems, so consider the crops you intend to grow.
Can You Put a Raised Garden Bed on Concrete?
Yes, provided the bed has adequate drainage.
Water needs to be able to leave the garden bed rather than becoming trapped around plant roots.
Geotextile fabric may also help prevent soil from escaping underneath the bed onto the surrounding concrete.
Does Raised Garden Bed Soil Settle?
Yes.
Freshly filled garden beds naturally settle as they are watered and organic material begins breaking down.
Check the soil level periodically and top the bed up with quality soil or compost when necessary.
Can You Fill a Raised Garden Bed With Compost Only?
It is generally better to use a balanced growing medium rather than filling the entire bed with compost.
Compost can be an excellent component of raised bed soil, but plants benefit from a balanced soil structure that supports drainage, moisture retention and healthy root development.
Ready to Fill Your Birdies Raised Garden Bed?
There are two straightforward ways to fill your Birdies raised garden bed.
You can fill the entire bed with a quality raised garden bed mix.
Or, for a taller raised bed, use suitable clean organic materials through the lower portion before finishing with a generous growing layer of quality soil.
Whichever method you choose, the next step is working out exactly how much material your garden bed needs.
