Deep raised garden beds 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. Fortunately, experienced member Noelle has shared a comprehensive step-by-step guide showing how to fill a raised garden bed.
If you plan on growing vegetables in raised beds, there is also a step-by-step guide to growing vegetables on the Bunnings website, which includes information about preparing your soil and the importance of mulch.
Also check out the how to grow vegetables video below. - Jason
Type of soil depends on what you plan to grow & the size of the beds. How easy the area is to access is also a consideration.
Measure the bed up to work out the volume you need, length x width x depth will give you cubic metres. So, for example, 1m x 2m x .3m = .6 of a cubic metre.
In a cubic metre there are 1,000L. This is important to know because potting mix & bagged soil mixes are sold in bags measured in litres. Personally if the volume was over about 250L I’d be using soil from a landscape supplier instead as it can get quite expensive but if access is difficult you may still need to buy bags.
You will find some good blends in 50L bags at Bunnings so that can make it more economical. If you do order from a landscape supplier then you’ll need to express the order in cubic metres. So half a cubic metre for example.
The type of mix you use will depend on what you plan to grow, veggies, flowers, shrubs etc. but whatever you grow make sure the mix is suitable for use in a raised bed or large planter box.
And don't ever, ever scrimp on the quality of soil or mix to go into raised beds or planters or pots. It's a false economy to try & save some money by selecting a cheap mix. - Adam_W
I have built quite a few raised garden beds. I usually get a delivery of dirt from the local hardware shop, which is usually a mix of soil and pig manure. Then I buy a few bags of mushroom compost, cow manure, and add dynamic lifter, and mix it all together and fill the garden beds. - kel
If ordering bulk soil you need to tell them that it's for a raised garden bed, the blend is slightly different and generally contains more sand to reduce shrinkage and improve drainage.
Gravel or finely broken rock can be put in the bottom if drainage is a possible problem but under most circumstances it's not needed. Sometimes material like that is used to bulk out the bed. Using waste rock is cheaper than filling the entire bed with soil as most veggies, etc. only need & use the first 20 to 30cm of soil depth.
If you do put any sort of drainage or bulking material in as a bottom layer make sure that you then cover this with drainage fabric before adding the soil. - Adam_W
First up, place some gravel, rocks, flattened old cardboard boxes, newspaper and pea straw in the bottom, this will keep weeds at bay and invite the worms to come and visit. You may also like to place a composting worm farm in the corner of your garden. Then get some good top soil or potting mix, I used Organic Potting mix, sprinkle a slow release fertiliser pellet. Then decide what you are going to grow and go for it.
For your information zucchini, snow peas and cucumber may be grown in raised beds with the assistance of veggie trellis, ease of harvesting. - Maursie
Placing black plastic on the inside of a steel garden bed helps with regulating the temperature of the soil. Since the soil in a raised bed is elevated above the ground, it will gain or lose heat faster than soil in the ground. I recommend putting the plastic on as it provides a benefit to your garden bed. I suggest using the GRUNT 2m x 5m Black 100um Builder's Film Handy Roll. - EricL
One year ago, I had left over Colorbond from when our house was built and decided to make a raised garden bed with that and scrap wood. One problem I had with a very low budget project, was how the heck do I fill a large bed with that much soil on a low budget? I couldn't dig it from the yard as we are on an inland island and it's all sand here and I only had a little bit of compost from the previous house.
One night online, I discovered Hugelkultur, which if I understand correctly, is an old German method of building up raised beds with logs, branches and organic matter and growing your produce in the soil above that. Then, as time goes by, the wood and stuff underneath will eventually rot down and become nice organic matter for your garden bed.
I back onto a forest, so I used debris along my fence line, which ranged from very thick branches, down to twigs and leaves.
It's almost one year later now , so next month I will remove the strawberries and broccoli I have in it now and will dig down to above the branches and give it one big turnover. That will be the first time all those upper layers have been mixed, so I'm keen to see what it all looks like after a year of watering, rain and having small crops growing on top.
I really did jump hard on the bottom forest debris layer and gave it a good soak, so maybe it was compacted enough to hold its shape as I'd imagine that thick stuff will take a long time to rot and break down.
I made a second similar looking bed and instead of the Hugelkultur method I built a base with drainage half way up on that one and filled with compost, Bunnings soil and old horse poo. That one has sunk a little more and does not seem to hold the moisture as well as the first one.
I turned over the soil deeply for the first time the other day and pretty much everything other than the big logs and branches at the bottom have broken down.
Smaller twigs pretty much crumbled in my hands. Any leaves or cardboard in the upper layers are unrecognisable.
Very happy with how it has turned out and I would imagine that it would be a few years at least, before those big logs and branches broke down at the bottom. - rattle