Skip to content
Metal raised garden beds are fantastic to both organize plot space and provide easy access for your yards or gardens. To determine the dimensions of a raised garden bed is so crucial that it can significantly impact the productivity and longevity of your plants. Unproper size of garden bed can either limit the number of plants you grow or make it difficult to maintain and harvest your plants, wasting soil, water, and fertilizer.
What is the optimum size of a metal raised garden bed? Width, height and length are all important considerations, as is spacing if you're planning to have more than one raised bed in your yard. After considering factors such as available space, purpose, and personal preference, you can determine the ideal width, length, and height for your metal raised garden bed. Remember that a well-designed garden bed is the guarantee of a bountiful harvest and many years of enjoyment.
Ideal Width Determination
One major goal of metal raised beds is to alleviate the need for gardeners to step into them. The maximum width of a garden bed is a matter of human ergonomics, it’s the distance an average adult person can reach across a garden bed from both sides to easily access all parts of it.
Ideally a garden bed should be no more than 4 feet wide if it is accessed from both sides, as this width allows an adult to reach just past the center from any side, giving optimum accessibility to the gardening area. If garden beds are to be accessed from one side only, the optimum garden bed width is 2 feet, which is half of the width of a bed that can be accessed from both sides.
A bed wider than 4 feet may require you to step into the bed, which can compact the soil and damage your plants. On the other hand narrow beds use almost as much materials as wider beds to construct, since most of the materials in a garden bed are used in the length of the sides of the bed. Making the ends a bit wider only uses slightly more materials, at a slight increase in cost. The downside is that narrow beds offer far less usable gardening space. The optimum size for a garden bed is therefore one with the largest usable garden bed width which can be easily accessed and used most efficiently at the preferred garden bed length, whatever that may be.
Ideal Height Determination
Metal raised garden beds are typically between 12 and 24 inches tall, although they can be higher or lower depending on your preferences.
The depth of a raised garden bed is determined by what will be grown in it, how often it needs to be watered, the surface it will be placed on, and height requirements for disability situations.
Most vegetables are fairly shallow-rooted, and have 80% of their roots in the first 30cm of soil, so they can be grown in a raised garden bed that contains 40cm. Culinary herbs such as thyme, oregano, marjoram, and mint also have quite shallow roots.
Deeper garden beds will hold more soil, which can get very expensive to fill, but the advantage is that they can hold much more water in the greater volume of soil, and need less watering in summer. They’re also better suited to root crops, such as carrots, or tall plants which can tip over and uproot in strong winds, such as sweetcorn.
If a garden bed will be placed over soil, then depth doesn’t really matter, as plants can root into the ground beneath if they require more depth, but on a hard, sealed surface such as concrete, pavers or asphalt, that’s not possible.
For gardeners with limited mobility, who have difficulty bending down, metal raised garden beds are used to make access easier. These garden beds are usually are waist high. The garden bed itself doesn’t need to go all the way to the ground though, it’s the height of the top that matters in such instances.
Ideal Length Determination
The length of a raised garden bed is not as critical as the width. It can vary depending on the available space and the number of plants you plan to grow, but remember that very long metal raised garden beds can be a hassle to walk and work around.
What most often happens with long beds is that people will walk through them rather than around them if they are low enough, which causes soil compaction, ruins soil structure, prevents water absorption, and makes it harder for plant roots to move through the soil! This is something any gardener would best avoid. If metal raised garden beds are too high to walk through and too long to walk around, gardening becomes a burdensome chore!
If garden beds are required to span long areas, it’s best to build multiple shorter beds. This method will use more materials and therefore be slightly more expensive, but the shorter garden beds will be structurally stronger as the end sections will only have to support shorter lengths of sides, making the structure more rigid. The use of shorter beds will also save a lot of effort and energy getting across the line of garden beds, which will make the experience of gardening much more enjoyable in the long run.