Corrugated metal raised garden beds are a great way to quickly get a garden up and going. They’re strong enough to be self-supporting and can last a long time. Some are stylish, suit the most discerning gardener, and are available in several heights.
We chose them because they can last in a tropical climate, and this is where we come in.
About 6-7 years ago, we took a Permaculture Design Certificate (PDC) course to help us become more resilient in our lives and food supply.
For many years, we had planted the odd garden with vegetables with varying success, mainly because of a fundamental lack of knowledge and understanding of the many things that could have made a considerable difference.
It was through the PDC that we came to understand soil, and for the two years after the PDC, we slowly put into place the required infrastructure and designs that have allowed us to now be self-sufficient in almost all vegetables, spices, and fruit.
The last critical item on our list was working out the raised garden beds, what type to use, and where to put them.
Our location was the deciding factor in all decisions. We live in the wet tropics of northeast Australia, where the wet season can quickly turn wooden raised garden beds into spongy mush.
While rotting wood is a fantastic way to build excellent soil, it can be murder on raised garden beds.
The expected lifespan of a wood-framed garden bed in this location is short, so just like any sane person, we looked at all sorts of viable alternatives.
The raised garden beds we needed had to last for at least a decade, potentially double this. The beds needed to be quick to make, and they had to look good.
The price was important and played a large part, but the cost over time was hard to calculate when the life of the beds was largely unknown.
We settled on the corrugated metal raised garden beds and ended up with two versions of them that are both good, but one rises above the other in aesthetics—more on this below.
The final choice was corrugated steel raised garden beds, and this post is about the questions we asked ourselves as we researched the topic. We hope the following can help you explore with information from actual self-sufficient organic growers.
Is corrugated metal good for raised bed gardening?
Corrugated steel garden beds are great because they are light, easy to put in place, can be whatever height you need, and can be color matched to suit your garden.
They come in many different sizes and a couple of styles that limit the sharp corners that can be painful if you walk into them. You should be aware of the disadvantages of these beds, and we discuss these in “Organic raised bed gardening, what are the disadvantages? “
The corrugated metal garden beds have a soft form that is nice to look at, and this can significantly help if you are looking for a stylish garden bed that still functions as a raised garden bed should.
The soft curves of the metal garden beds look great from our perspective, and we expect them to stay this way for years. It is easy and pleasant gardening.
A word of warning. These beds, while very good, can have an issue with soil temperatures near the metal sides in certain conditions. It is covered entirely in “Does soil in metal raised garden beds get hot?” We recommend you read it before buying this type of garden bed.
How long can corrugated metal raised beds last?
The consensus lifespan of a galvanized metal garden bed is at least 30 years. Some metal garden beds are not galvanized but have an aluzinc coating that protects the metal from corrosion. Their lifespan is unknown to us.
Factors outside the metal garden bed maker’s control determine the lifespan; the primary one is the soil pH because acidic soils are more corrosive than neutral soils.
There are other factors to consider with these beds because they all use fasteners to hold them together. These fasteners can sometimes rust before the sheet metal shows any deterioration.
There are reasons why this premature breakdown of the fasteners happens, and often it is to do with the different metals that are in contact with each other. It is a galvanic corrosive reaction caused by an electrochemical process in which one metal corrodes preferentially over another. This galvanic process can be accelerated in the presence of moisture.
Garden beds get watered, so we can unwittingly speed this behavior up. Where stainless steel fasteners are used and the corrugated metal is zinc-coated, there should be only a little-to-no galvanic reaction, even in acidic soils.
What type of corrugated metal garden bed is best?
We have two styles, as we mentioned at the start of this article, and they are both made from the same material. One is manufactured locally by a roofing plumber from spare roofing sheets that they roll into the oval shape shown here.
The next raised garden bed and our preferred type is a kit form raised garden bed that is Australian made but is available in the USA and several other countries.
The fasteners are stainless steel, and the garden beds come with safety edge capping that is UV stabilized and is said to last many years. It can also survive minus 20C (-4F).
If you are looking for fast and easy methods to cover the edges of the metal raised garden beds, “Can edges on corrugated steel garden beds be made safe?” is worth reading. We had this issue.
After all of our research, we have concluded that the kit-form garden beds made by Birdies are the best for our situation. The reasons are many.
The main one is the kit allows for several different shapes and sizes to be made from one kit, so there should be a shape and size that will fit your space. The fasteners are suitable, the corrugated metal sheets are color coded on the outside, and the color is your choice from a reasonable selection.
The beds are reasonably easy to put together and require nothing more than a spanner and a screwdriver, but a battery drill with a socket is far quicker.
Should corrugated metal garden beds be lined?
There should be no reason to line a corrugated raised bed if you purchase one from a reputable manufacturer.
The only time it may make sense is if, for some reason, your soil is highly acidic, but then if this is the case, there is little chance of growing a decent crop in that soil.
If the soil is acidic and the fasteners are just carbon steel screws or bolts, the risk of galvanic corrosion can be higher, so lining the inside of the bed might be worth considering. Stainless steel fasteners eliminate this need, though.
There are other reasons why lining a bed makes sense, but this is for animal intrusion control from below the bed, and a fine stainless mesh placed at the bottom of the bed can stop this straight up.
Do metal raised garden beds get hot?
The side facing the sun during the day does get hot, affecting the moisture content of the soil on that side of the garden bed.
There are a few potential methods to counter this heat buildup, and we are personally looking at the alternatives.
The first is to hang a temporary curtain of shade cloth material on that side of the raised garden bed, and as this is not a permanent fixture, it stays in place with clothes pegs or similar.
The following method is more permanent and is a heat reflective ceramic paint coating that will help keep the metal cooler. This type of paint is often used in the marine industry to help keep the cabins and wheelhouses cool. It is a more costly method but is more permanent.
The final method we are considering is to grow plants that hang outside the garden bed and may be able to shade the steel face trapping the heat. We are leaning towards the shade cloth to start with and will see how that goes first.
The heat can dry out your soil and cause it to be less fertile for the next season, so it is worth mentioning this article on “How to maintain organic soil in raised garden beds. ” It is how we approach soil conditioning.
Does metal rust affect plants?
Rust from a raised garden bed is probably not going to be a concern; however, the structural integrity of the garden bed is of concern if rust is present.
One thing to be aware of is that the edge of the garden bed is the only place that can rust, and watering will wash any minerals and elements away from your plant’s roots.
Some plants may have roots near the edge of the bed, but for the most part, the plants will be ok.
In bad cases, there can be an issue with the iron buildup in the soil where rust is heavy and the soil is very acidic. As stated above, strongly acidic soil is not a healthy medium to grow vegetables and is likely to cause plant problems, not rust.
Rust is simply a form of iron oxide, and plants can benefit from this in some cases if the surrounding soil is a bit light-on for plant available iron.
Is galvanized steel toxic for vegetable gardens?
Galvanized steel is safe for garden beds, and the only way galvanizing can harm plants is through highly acidic soils like acid sulfate soils.
These types of soils can dissolve hot-dipped galvanized coatings in a short time and will be the end of your garden bed. It is rare for these types of soils to make their way into the garden, but it has happened before, so we have mentioned it.
We prefer to use soil that we have made ourselves, as described in this article “Making organic soil for raised garden beds. “
Are galvanized steel raised garden beds ok for organic food growing?
Galvanized steel garden beds are adequate for organic food growing. There is no need to apply chemicals or special treatments to the steel garden beds, and the soil should not interact with the metal in any way that can be dangerous.
Suppose the garden beds are from a reputable manufacturer who uses quality materials to make them. In that case, there is little to zero risk to the soil or the plants, so they are outstanding for growing organic vegetables in raised beds.
We would use galvanized steel garden beds if they were available to us. We consider ourselves organic gardeners and use natural fertilizer as described in this article: “Improve your garden soil with rock dust and chickens.” we have no doubts the garden beds are safe to grow food.
And that concludes why we recommend using corrugated metal raised garden beds.
We have no regrets about the metal raised beds we have here. We have a total of 10 raised beds so far, and we intend to get several more when the next phase of our permaculture design takes shape.
We love them and suspect you will as well once you start growing from them. If you are interested, we have another article on “using raised garden beds” for more information.
Article by Tim Blanch for TheTropicalHomestead.com. He is a qualified Permaculture designer.