What materials can I use to build my raised garden bed?
The design and construction of a raised garden bed is in itself a really simple thing, after all, all we are really building is a retainer for your garden bed. Many vegetable gardeners who use more traditional methods build up their soil into humps or mounds to assist drainage and a raised garden bed simply takes this a step further by creating a retaining wall around the garden soil to prevent its loss.
This retaining wall can be constructed from any number of materials and you can choose to use anything at all that is freely available providing it is inert and will not leach any dangerous substances into your soil that can taint the taste of your crops or make them toxic. A prime example of this is pine that has been treated with CCA (Chromated Copper Arsenateor), a commonly used toxic chemical that was widely used in the past to treat timber that was then subsequently used for many purposes including children playground equipment and frames for raised garden beds. There are concerns that CCA may be leached into the garden soil from the timber and can be absorbed by your plants. This makes wood that has been subject to this treatment a questionable choice, particularly since a common objective of home vegetable gardeners is to cultivate chemical free produce.
Wood is by far the most common material used to create the frame for a raised garden bed as it is fairly cheap, long lasting and strong. It is not necessary to use new timber, second hand materials are perfectly fine as long as you bear in mind the previous paragraph about treatments that have the potential to leach into the soil and taint your produce. If you have a doubt as to the safety of a particular source of timber it may be wise to simply use something else. One of the most impressive raised garden bed vegetable patches I have seen was constructed using second hand railway sleepers supported by short wooden stakes at intervals on the outside of the garden bed to stop the sleepers from collapsing outwards under the weight of the soil they contained. This particular complex of five or so raised garden beds impressed me by the size of the beds and the fact that the frames were laid out during the space of a morning without a single nail or screw. The stakes were simply driven into the ground with a hammer. When selecting wood for your frame try to use hardwood rather than softwood as it will last much longer.
Making Use of Wood or Concrete Blocks
Although wood may be a more traditional choice for building a raised garden bed I have also seen concrete blocks used with good effect. When placed in a single row concrete blocks need not be cemented and will provide a good strong retaining wall. If I was ever required to build a raised garden bed that was waist high, which can be very suitable for elderly or infirm gardeners, I would prefer cemented concrete blocks over wood as I feel that this would provide a stronger and longer lasting frame. Similarly, bricks can be used instead of concrete blocks either cemented or simply laid in place however bricks are lighter and can be displaced easily if turning soil over or adding compost, manures and such so joining the bricks together with cement seems to be a better proposition under these circumstances.
When compared to the price of a wooden frame concrete blocks or bricks are generally a more expensive option but the wood will eventually rot and those seeking a very long term solution may find the “bricks and mortar” to be the better choice. I prefer a wooden frame because I feel it provides a more natural appearance which I find pleasing.
Natural Stone or Rocks
You might also consider using natural stone or rocks to construct your garden bed frame but cement tends to be necessary to plug the wide gaps that are caused by the irregular shapes that natural stone or rock comes in. As the saying goes, there are no straight lines in nature and finding a combination of rocks that fit together perfectly is nearly impossible.
Many hardware and garden shops stock raised garden bed kits which compare favorably in price to buying the materials and constructing the frame from scratch. One such kit that has caught my eye recently uses sheets of curved galvanized iron and is available in either 12 inch or waist height. The waist high version is a couple of hundred dollars and is something of an investment but when assembled even a die hard fan of wooden frames such as myself had to admit that they were very attractive and would look good in any garden, with a range of choices from bright and gaudy to subtle earth colors.
There are many other choices for material to use for your garden bed frame, some more natural appearing and some easier to work with than others. Whatever you choose, make sure it is a material that is friendly to the environment, enhances the appearance of your garden and surrounds and is one that you are comfortable working with.