We have ten metal raised garden beds in our yard, and two of them always seem to underperform in production and quality.
It took some time to work out the problem with these garden beds, and it ended up that these two beds were too narrow to grow vegetables reliably.
As our website name used to imply (update-we used to be selfsufficienthomelife), we are self-sufficient in several food items, but this is only possible when all things fall into place. This includes getting the design right on the garden beds.
How wide should a metal raised garden bed be?
We have found that the optimum width of a metal raised garden bed is 3ft. There are several reasons, as we explain below, and your geographic location will present you with different opportunities and challenges related to the causes we mention.
Metal raised garden beds are part of what we consider mainframe design. They can present challenges not openly discussed in some parts of the internet. Below are a few problems we have faced regarding metal raised garden beds.
Is there a minimum width for a raised garden bed?
In our situation, the minimum width for a garden bed “in our location and climate” is 32inches (820mm) or thereabouts. Your location and climate will likely change the dimensions, as you will see below.
We live in a tropical climate in Northeast Australia. The sun angles significantly affect our growing conditions, particularly in metal raised garden beds. Still, we didn’t know how much the sun affected the garden beds.
So, we ran a test where we took a series of temperatures in the soil at stepped measurements from the edge of the garden bed while the sun was striking the side wall.
The results can be found in “Does the soil in metal raised garden beds get hot?” We were very shocked at the variation in readings. We strongly recommend reading this.
The discovery in the above-linked post set us on a path of redesigning two of our garden beds. They were too narrow for growing vegetables with any degree of confidence of a worthwhile return in the harvest.
These garden beds are the modular Birdies type. They can be rebuilt into a far better shape without any cost or loss of materials. Presently, they are 23 inches (590mm) wide in the narrow form we unknowingly constructed them in. This is far too narrow when the information gathered in the linked post above is considered.
The sun is close to being directly overhead for several weeks of the year where we live, so this has the sun at its nearest point to earth, right where we are. During the hours on either side of midday, we have the most buildup of heat in the soil at the garden bed wall.
The direct overhead sun’s effects can be compensated for with mulch on the garden bed surface. Still, the sun that hits the side walls of the garden beds is where the heat buildup happens.
Your location will be different, with the sun’s intensity sure to change. However, suppose you use metal raised garden beds. In that case, there is a high probability that you will have a similar temperature effect at the soil edge as we did, but the variation may be less.
We recommend sun mapping your yard to help you gather information on how the sun angles will interact with your garden beds. The information in that post can help guide you. With some good design work, you can avoid some of the hot soil issues we are now working to fix.
So getting back to the question about minimum width. The measurement we have supplied is only based on the next smallest sized garden bed we have, and one where we have success growing our vegetables.
What is the maximum width for a garden bed?
The maximum width of a raised garden bed should be based on the reach of the gardener’s arm to the middle of the bed. We have found that the best garden beds are 44 inches(1120mm) wide. This allows plenty of room for plants; we can still get in amongst the vegetables to tend them as they grow and pick what is required for the table.
If the garden beds were any wider, they would become uncomfortable to work with and could be the reason for a sore lower back. Isn’t this one of the main reasons why people get raised garden beds in the first place?
This image shows the narrow bed on the left. The rolled metal garden bed on the right is the minimum size we will accept.
Does the type of garden bed matter with width?
The material that the garden bed is constructed from should be a major consideration for the width of the garden bed. If the material is known to transfer heat, we recommend the minimum size mentioned above.
Just remember that we stand outside the bed as we do our gardening, so reaching to the middle is vital. If the material you make the garden bed is thick, like concrete blocks or similar, you will lose some of the growing area because of the side wall thickness.
This is where the thin-walled metal raised garden beds shine, but they can have their downsides with heat issues.
The heat is not so prevalent in garden beds constructed with other materials. To help you decide what material you want, “what is the safest material for organic raised bed gardening?” looks at possibilities.
What is the best size for a raised garden bed?
The best size for a raised garden bed is related to your backyard and how you can design the area to maximize your growth potential. We have a post that details what direction is best to have raised garden beds facing, and it can give you some ideas on how to look at your yard with sun and slope in mind.
Then with that information in hand, look at access around the garden beds where you think they would be a good fit. We find that we have a few garden beds too close to each other, and we sometimes have trouble getting wheelbarrows around them.
So, with sun angles and access around the garden beds sorted, particularly at the ends of the beds, you can work out the optimum size for your garden.
Every garden has different sun aspects and space limitations that will impact the ease of movement in and around your garden beds. We recommend doing the design work before even buying a single garden bed.
Choosing the correct sized garden bed for your situation is often skipped in a rush to get started with growing your vegetables.
Knowing why some beds fail while others grow well can be the difference between being self-sufficient in something or buying it because you don’t have a “green thumb.” We hope this post, and this whole website, can save you some cash, time, and mistakes.
Article by Tim Blanch for TheTropicalHomestead.com. He is a qualified Permaculture designer.