Raised garden beds are a great addition to any backyard, and I’ve discussed the benefits in the past. They can be built for practical reasons like fixing poor soil or to help save your back bending when harvesting crops, or they can be built and used with design intent in mind, like as a retaining wall, or to highlight flowering plants.
Whatever reasons you have for wanting them, here is our guide to building raised garden beds in your backyard.
Different Types of Raised Garden Beds
Raised garden beds, as the name would suggest, are beds that are raised above the original level of the ground in your garden. This can be as little as a 30cm mound, or as big as a metre or two.
If it’s simply a raised mound, then it’s most likely just good soil built up to a height, rounded on the sides with an edge dug in. This is pretty common for planting flowering annual beds, and can easily be turned and worked each time you want to replant it.
Using these style of raised beds lets you add contours to a landscape, and help direct a visitor around it, by making obvious walking routes. You can also add a lot of height variations to your designs by using these small raised garden beds.
They also work really well in run off water and erosion control. These raised mounds generally don’t need anything surrounding them to act as an edge, but you could always encircle a mound with some plastic edging, just to help secure some of that loose soil.
Bigger raised garden beds are generally built structures that sit above the ground, and are filled with a planting medium, and planted with flowers or crops. These are often at least 30cm deep (about the minimum soil depth you want for a veggie garden) and have a solid, straight structure on the side to hold in the large amount of soil within.
Most people use these for harvest crops. The reason for this is that you can control and monitor everything that goes into your garden and into your plants. Creating a soil profile above the ground means that only the good stuff you throw in gets used by the plant.
This is great if you’ve got hard, rocky or saline soil, or soil with nutrient or pH issues. Getting your garden up above these problems can be a great way to utilise your space without spending a fortune fixing the ground.
You can pick up a bunch of these types of structures in all different sizes and shapes from most warehouse garden stores and nurseries, or you can whip your own up with some timber, bricks, or galvanised steel.
How to Build a Raised Garden Bed
So you’ve decided you want a raised garden bed, and want to get stuck into it yourself. Great! Luckily for you, it’s actually a really simple process, and with just a little bit of work, you can have a great raised garden bed that suits your needs.
Step 1. Mark the area
Pick the spot you want your raised garden to go. You need to consider what the garden is going to be used for, and what you’re planning on planting here. If you’re planning sun loving plants, then obviously it needs to be in a sunny spot.
If you’re planning on planting crops, then consider things like access to water, or how hard it will be for you to carry back your bounty. You also need to consider how big you want your garden to bed. Is 1m x 1m really going to be enough room to plant up your own little tulip floral display? Or is a bed the size of a swimming pool really that practical?
Stopping and having a good think is the best advice here. Common sense should point you in the right direction. A good tip is to break up beds and do a couple dotted around the place, to make use of different conditions throughout your backyard.
Once you’ve picked your spot, grab some spray paint and mark the area as best you can. If you’re using an out of the box contained you’ve purchased, then make sure the area matches it.
Step 2. Prepare the ground
Now depending on what you’re putting your raised garden bed on top of, and how high you’re planning on raising, this step can be either quick and simple, or a little involved. If there’s any ground vegetation like turf, you want to dig this out completely.
Using a shovel, cut around the outside of your marking, then strip the top layer of soil containing all the roots of the grass with it. This will mean that you wont have any unwanted grass or weeds shooting up through your raised bed, and makes it way easier to get the site level.
If you’re planting onto a hard surface like compacted rocky dirt, or concrete, then just give it a good sweep and make sure there’s no small weeds in cracks that could cause the same problem.
Once we have our site cleared, it’s time to level it out. Dig out or rake around your soil to do this. You don’t need to get out your spirit level for this one, but you want it to be pretty much level. This will help when you set up any structure that you’re building, and will ensure even water movement as it moves through the soil into the ground.
The final step for preparing your ground is an optional one, but one I would really suggest following. It involves laying some geo-tech fabric or silt fencing on the ground. Basically this stuff is woven material that catches and holds sediment, whilst allowing moisture to pass through.
The reason I suggest putting this layer in is that firstly, it’ll stop any of your soil falling out the bottom if you’re planting onto a hard surface, but secondly because it will help hold in and preserve any organic matter and organisms you get or add (like worms), and keep out a few of the nastys that you’re trying to leave behind in your old soil.
A lot of people are happy for their raised beds to connect with their ground soil to act as a soil conditioner and improver for the gardens around them, and this can be true, so it’s very much an optional step.
Step 3. Building the structure
If you’re planning a simple little mounded soil garden, you can skip forward to Step 4, but for everyone planning a larger raised bed with a structure, here’s your time to shine.
This is time you get to put together your out of the box kit, or get out the measuring tape and hammer to build your own.
The options are endless as to what you can use as a raised bed container. The most common you will see are made of hardy material like galvanised steel, or timber sleepers. But you can also use bricks, rocks, or get crazy and use things like old steel drums or washing machines!
Whatever you use, make sure it’s not going to rust; can support the weight of all the soil behind it, and can provide a nice level and even container for your soil.
When you’re set up with the structure, grab some more geo-tech fabric, and line the sides with it. This will help stop any soil escaping through joins or holes, and helps create enough separation between your structure and the soil to allow air and moisture to pass through, meaning healthier soil.
If you’ve got a sizable raised garden bed, it’s definitely worth installing some ag line in as well. Ag line/pipe is a flexible plastic tube with holes all along it. This is covered with a geo-tech sock, which keeps the soil from getting into the holes and blocking the tube.
Installing this will help get air flowing through the bed, right down into the deepest layers. This will help keep the soil from getting water logged, and all the aerobic microorganisms in your soil will be doing their hard work all the way through your bed.
It gives the added bonus as well of being able to stick your hose down and watering directly to the root zones of plants during sunny hot days. Lay the ag line about ¾ way along the bottom of the bed, then up to the top corner to just above where you expect soil level to be. Cover it with a little cap to stop anything finding its way down.
Step 4. Add your soil
This step is the real bones of your raised garden bed, and is the most important one to get right. Regardless how large your raised garden is, you need to have good quality soil full of good organic matter for your plants to grow in to.
For most gardens in Australia, I would suggest a 50/50 blend of good quality garden or top soil from your local landscape supplies store and organic compost. A tip I like to use is to mix up my types of compost, to have a variety of sources that your organic matter is coming from.
This is a good way to make sure you’re getting a good spread of microorganisms and nutrients for your plants to grow. Things like composted chicken or cow manure, and mushroom compost are pretty good bets, or your own if you have it!
Once you’ve got your soil mixed, its time to fill your beds. If you’re filling a large structure, be sure not to compact it down when you’re filling. Allow for about a 10% drop in height once the soil has settled after a couple of days as well.
For smaller beds, you want to make a flat -topped mound in the middle of the area, and smooth the edges off. Get it to the height you want, and gently, but firmly pat it down to hold it in place. Don’t be too worried though, once you plant it up, the roots will hold most of it together.
Step 5. Plant that garden up!
Once you’ve got your raised garden bed built and full of soil, it’s time to go nuts with planting! Whether it’s showy flowers and shrubs, or your own little produce garden, your new raised garden bed should be perfect for everything you need. Enjoy!
In the past I’ve installed my own raised garden beds from Bunnings, which you can read about here – but as you can see, it’s not too much work to build up your own garden beds, and can be a great project with the rest of the family. So what are you waiting for? Get in there and give it a crack!