Growing Vegetables in Raised Beds
Part Three of the Vegetable Patch from Scratch Series
Part 1 and Part 2 in the series looked at where to locate your vegetable patch. This week, I am discussing options for growing vegetables in raised garden beds.
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Raised garden beds can be great for those with mobility issues. They can help define a space, restrict access to pets and look very aesthetic. Raised beds seem to be the default option for those wanting to grow vegetables. However, in many instances gardeners are better off saving their money and growing directly in the ground instead. If you are keen to explore raised garden bed options anyway, then here’s a few considerations for you.
Material choices
There are plenty of material choices available for raised garden bed construction. Ultimately it will come down to whether you prioritise environmental concerns, durability, aesthetics or cost.
Treated pine
I believe that treated pine (including ACQ and “ecowood”) are not suitable for raised vegetable garden beds and have a much larger environmental impact than cypress. Radiata pine is usually grown in large monocultural plantations. This contributes to soil erosion, as well as loss of habitat and biodiversity. Once harvested, the timber requires large amounts of transport fuel, and energy and chemicals in treatment plants. As pine is not naturally long-lasting, treating it involves drowning the timber in chemicals to kill termites and fungi. The pesticide and fungicide protect only the surface of the timber, so if you cut it, it needs further treatment. The timber is also heat-treated to reduce warping and shrinkage, which uses a lot of energy. The only benefit of treated pine is that it is very cheap and easy to obtain.
Cypress
Cypress, Cupressus macrocarpa, is native to North America but has been planted widely across Australia. Used as wind breaks across farms, the now over-sized trees are being logged to provide a sustainable timber option. Properties across Victoria are providing the timber, and a few sawmills are producing sleepers from it. Because it is harvested locally, the carbon emissions associated with its transport are relatively low. Cypress sleepers are naturally resistant to termites and decay, although they are perhaps not as long lasting as some may have you believe. The better the quality of your soil, the faster it will rot the timber. Very good quality soil will reduce the life-span of a vegetable bed made from cypress sleepers to around five years. Ten years of use would be a great outcome for cypress timber beds.
Red gum
Red gum and other hardwoods all come from slow-growing trees. To my knowledge there are no red gum plantations actively being harvested, and therefore all red gum sleepers have come from old-growth forests. The advantage of red gum sleepers is that they will last a lot longer than cypress ones.
Reclaimed railway sleepers
Reclaimed railway sleepers are also made from red gum. Garden beds constructed from these will last decades. Railway sleepers are incredibly heavy and can be difficult to work with. They’re also very expensive. My main concern with using them in the vegetable patch is that they have probably been exposed to high levels of contaminants during their previous useful life on the railways. Frequent herbicide application, asbestos from train brakes, oil and other chemicals are likely to be present on these sleepers.
Corrugated iron
Timber has the advantage of insulating the soil within the raised bed. In contrast, corrugated iron is likely to influence the soil conditions right at the edge of the bed but unlikely to have much influence beyond a few centimetres. Corrugated iron beds are relatively cheap to buy but I recommend looking for beds constructed out of Australian-made steel. Cheaper versions may be made from steel that is refined in countries such as China and shipped to Australia, generating a large ecological footprint. Even worse is that often that steel is refined from iron ore dug out of Australian soil in the first place.
Brick
I like brick as a garden bed option. It doesn’t rot like timber options will, and as long as it is set up correctly then a raised bed made from bricks should last centuries. Obviously, you’ll want to make sure your vegetable patch is in the correct position if using bricks! Bricks are thick, and that means that you’ll need a garden bed with larger external dimensions to hold the same amount of soil as say a corrugated iron bed. Bricks require a lot of energy to be fired, so new bricks are not a very sustainable choice. It might also end up quite costly to buy the bricks and have a bricklayer build the beds for you. I’ll be using recycled bricks for the next iteration of our kitchen garden.
Best choice for environmental and safety concerns: Cypress or recycled bricks
Best choice for durability: Bricks or red gum sleepers
Best budget choice: Treated pine or corrugated iron
Best choice for aesthetics: That’s a personal choice!
Size considerations for raised beds
Kitchen bench tops are mostly the same size to accommodate our arm span. If they were any bigger you couldn’t reach the centre!
The same principle applies to designing garden beds. Raised garden beds should be no wider than you can comfortably reach across to pick your produce. I recommend that the beds are no more than 1200 mm wide, if you have access from both sides of the bed, or 600 mm to 700 mm wide if they are sited against a wall. I regularly conduct site consultations for clients with huge raised garden beds 4 or 5 metres wide and long. It is impossible to tend or collect produce from these gardens without walking all over them and compacting the soil. Long and narrow beds are far better.
If you are tall and you are the only person who will use the garden beds, then these can be slightly larger. If young children are going to be using the garden beds, then consider reducing these dimensions.
Similarly, bigger is not always better when it comes to the height of your raised garden bed. Often my clients will ask for a raised garden bed 80 or even 100 centimetres high. In most instances this is because they have limited physical capacity – they can’t easily bend over. That height is okay for growing small crops such as lettuces. However, if you want to grow tomatoes the story is very different. Sure, it is easy enough to plant your tomato seedling at 1 metre height, but as the plant grows, it will soon get to 1.5 to 2 metres tall, measured from the top of the bed. Far better to bend over once to plant (or get someone to do it for you) and then not need the ladder all summer to harvest produce.
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This post is one of many in my gardening series Vegetable Patch from Scratch. See the series index for a list of other topics in the series.
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We have recycled tomato/potato/ grape crates bought from a local winery. We have made them into wicking beds and have greatly reduced our watering and worry. A win also on the rabbit count - too high to get in.
I’m constructing our raised vegetable beds out of cypress. Have you had any experience with applying Ecowood treatment to extend the life of the cypress? I’ve bought some from Canada and I’m planning to give it a go. It seems very highly rated online and the organic designation really appeals. Any thoughts?