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Australian Guide to Building a Raised Garden Bed

Raised garden beds have become increasingly popular over the last few years as a way to grow your own produce without having to deal with the soil in your garden.

Raised garden beds also make tending your crop easier because you don’t have to bend down or do any heavy digging.

Why build a raised garden bed?

There are many reasons why you would want to build a raised garden bed.

Firstly, you have total control over the type of soil that your vegetables are growing in. This means that you won’t have to spend hours tilling the ground in your garden and adding amendments to the soil to make it suitable for growing your produce.

Raised garden beds are also great if you don’t have a large garden or you live in a unit with a small courtyard.

Some raised garden beds are also portable. So, if you’re a renter, you can easily take it with you when you move.

Lastly, raised garden beds are ideal for older gardeners or those with mobility issues because you can raise the bed to waist height which eliminates the need to bend down. This makes looking after your garden so much easier.

Types of raised garden beds 

Raised garden beds come in all shapes and sizes. You can build one from scratch using recycled timber, sleepers, corrugated iron, bricks, or even Besser blocks.

Raised garden bed 6 | Plant care

In addition, there are numerous kits available made from a variety of different materials. These can be made from plastic, metal, or timber. I’ve even seen large wooden crates for sale like the ones you see at produce stores that are ideal for use as a raised garden bed.

Then, there are some very sophisticated kits available that include their own irrigation system, wicking beds, and even covers to keep the insects at bay.

While these can cost more, they can be a great way to start your own veggie garden if you’re not too handy with the tools.

How to build a raised garden bed

Raised garden bed | Plant care

The easiest way to build your own garden bed is to use recycled timber.

You want to ensure that the timber has not been treated with CCA as the nasty chemicals used for this can leach into the soil. CCA stands for copper and chrome arsenate.

Here’s a simple guide to building a raised bed that is 2.5 metres long and 1.25 metres wide, adapted from this guide by Gardening Australia.

Materials needed:

  • 4 sturdy timber posts that are 70 cm high
  • 2 solid timber planks that measure 20 cm x 5 cm x 1.25 metres for the short sides
  • 2 solid timber planks that measure 20 cm x 5 cm x 2.5 metres for the longer sides
  • Landscaping fabric to line your bed if you want to use it
  • Screws for securing the timber and tacks for securing the landscaping fabric

Tools needed:

  • A drill for predrilling the holes for the screws
  • A screwdriver for securing the screws
  • Large clamp for holding the timber planks to the posts while securing them
  • A spade or other digging tool to dig the holes for the posts

Instructions for building the raised garden bed:

Prepare the area by removing weeds and grass. Remember to choose a sunny spot for your veggie garden. 

Sink the posts, around 10 cm deep into the ground. You don’t have to concrete them in because the soil will hold them in place.

Start on one corner and attach one of the shorter planks to the post with screws. You should predrill the holes to make it easier and use the clamp to hold the plank in place to make sure that it gets secured nice and tight.

Secure this plank to the post on the other end and then add the second plank on top of the first one to create the height and secure it.

Do the same with the other short side by securing the planks to the posts.

Next, you want to add the planks for the long sides. Start with one side and secure the lower plank and then add the second plank above it. Repeat this with the second long side.

Your raised garden bed is now complete and you can start to fill it.

The best wood for a raised garden bed 

One of the best timbers that you can use to build a raised garden bed is recycled hardwood. This includes sleepers.

You can also use treated pine but make sure that it is H4 treated and ideally not treated with CCA.

While CSIRO has said that the risk from using CCA treated timber for vegetable gardens is within tolerable limits, for growing vegetables, many people prefer to not use treated timber.

H4 treatment can be conducted using a non-arsenic-based preservative that is termite resistant and suitable for outdoor use. Bunnings have a range called H4 Treated Pine Sienna MicroPro that could be a good option.

Should you line your raised garden bed?

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In Australia, it’s not an absolute necessity to line your raised garden bed since we don’t have digging garden pests such as moles and gophers. 

However, there are a couple of reasons why you might want to. Firstly, if the ground that you’re placing the garden bed on was heavily infested with weeds, lining it will provide a good barrier.

Secondly, it will stop the soil from moving out of the bed as you constantly water it.

Finally, if you’re placing your raised bed onto concrete or another hard surface, you definitely want to line it to stop the soil from staining the surface below.

To line your raised garden bed, only use good-quality landscape fabric, geotextile fabric, or weed matting that will allow water to flow through freely.

Never use plastic as this will retain the water at the root level and you’ll end up with root rot problems.

How to fill your raised garden bed 

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Filling your raised garden bed is easy when you use the layering method.

Here’s what you need to do.

Materials for filling the raised bed:

Instructions for filling the raised garden bed:

To cut down the cost if you’re buying compost for your raised bed, fill the bottom half of the bed with garden soil.

Use the landscape fabric to line the base and the sides of the bed. Use tacks to hold this in place. This effectively creates a barrier for the roots of the plants but will still allow the water to drain through. This part of the process is optional, however.

Next, you want to layer the remainder of the bed with animal manure and compost. Start with a layer of animal manure and then add a layer of compost.

Add some more manure and another layer of compost and top the bed with a layer of straw or sugar cane mulch.

Other tips for starting a raised garden

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Once you have your raised garden bed all set up, you should consider installing some type of irrigation system so that you don’t have to hand water on a daily basis.

Raised garden beds have excellent drainage, so on hot summer days, your bed will require more water than if you were growing in the ground.

However, if you use a drip irrigation system and connect this to a timer on your tap, this task is made much easier.

Another thing to remember is that the soil and compost will need replenishing from time to time, especially if you don’t use a liner.

This is actually a good thing because you can add compost to your bed in between plantings and replenish the nutrients at the same time.

FAQ

What do you put in the bottom of a raised garden bed?

If you’re raised garden bed is placed on soil, place a few layers of newspaper and cardboard in the bottom to suppress the weeds. You can also line your bed with good-quality weed matting or geotextile fabric that will allow water to drain freely.

How deep does a raised garden need to be?

The minimum depth of a raised garden bed should be at least 30 cm. However, if you build the bed a little higher, it will make it easier to tend the crops without having to bend down as much.

What are the disadvantages of raised garden beds?

The two main disadvantages of raised garden beds are that they’re more expensive to set up in the beginning and that they will require more frequent watering as the drainage is so good. However, if you install an irrigation system and have this on a timer, it won’t take up a lot of your time.

Photo of author

Annette Hird

Annette Hird is a gardening expert with many years of experience in a range of gardening related positions. She has an Associate Diploma of Applied Science in Horticulture and has worked in a variety of production nurseries, primarily as a propagator. She has also been responsible for a large homestead garden that included lawn care, fruit trees, roses and many other ornamental plants. More recently, Annette has concentrated on improving the garden landscape of the homes that she has lived in and focused a lot of energy on growing edible plants as well. She now enjoys sharing her experience and knowledge with others by writing articles about all facets of gardening and growing plants.

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