Raised Garden Bed Materials: What’s Good?
Choosing the right raised garden bed materials is crucial to building a solid garden. Compare and contrast varying raised beds here!
There are so many options when it comes to raised bed garden materials that it could make anyone’s head spin. When you’re deciding how to build your garden from the ground-up or how to make additions to an established garden, you want to go into the planning process informed and aware.
The truth is that there is no perfect material on the market. When you decide to create raised garden beds, you have to weigh your options based on the conditions of your region and, more specifically, your garden. There are garden bed kits you can buy, but too many options can lead to confusion.
That’s why we’ve developed this piece that helps you organize your thoughts around which raised bed materials are best for you and your situation. We’ll discuss each material and the advantages and disadvantages of each based on regional and financial factors, as well as how difficult the materials are to work with.
Now, let’s talk about raised beds of all kinds!
Metal raised garden beds are made of different steels that are sometimes sold in a kit, and sometimes put together from reused corrugated steel. You can build raised beds from cheaper reclaimed steel, corten steel, or painted steel. Some are expertly crafted for durability, while others aren’t as good.
Epic Gardening sells metal raised beds made by Birdie’s, which are the best metal raised beds on the market. You can find Birdie’s beds in our online store. But before you spring for them, let’s discuss their use in organic gardening.
Advantages of Steel Beds
Steel beds have thin sides that take up less space in your yard, garden, or field. They won’t take up as much as a wooden bed will. In particular, steels that are made of alloys are designed to last a long time. While there’s a lot of talk about how heat is bad for steel raised beds, this isn’t a concern. Steel beds can hold up to both hot and cold conditions and don’t experience significant temperature changes over other types of raised garden bed materials.
You might think steel raised beds aren’t cost-effective or wonder if their longevity doesn’t match their price. However, the cost of lumber often makes metal beds more affordable, and they last much longer. A good galvanized steel or corten steel bed lasts for at least 20 years due to varying coatings, whereas a wood bed generally doesn’t even last 15 years.
As for the actual cost, you’re likely to find some variability between distributors. From our shop, coated aluzinc beds and corten beds range from $120 to $300, depending on their size. They hold garden soil well, and unless there is some chemical imbalance, such as high salinity or chemical contamination of the soil, they hold up for decades. This makes them one of the best materials for raised beds today.
Most steel beds (save plain galvanized steel) come in a kit and are easy to build, requiring no power tools and no need to drill pilot holes. This is the case for all Birdies beds. Conducting maintenance on the beds is easy too! There’s very little you need to do to keep them up, and they can be disassembled and transported easily.
Disadvantages of Steel Raised Beds
Galvanized steel beds that lack a coating or treatment, like repurposed stock tanks, won’t last as long as other coated or heat-treated beds will. They are prone to rusting out over time, meaning stock tanks won’t last as long as a wooden bed. They are exceptionally cheap, but chemicals from the manufacturing process may leach into garden soil and end up in food crops.
A more acidic soil mix or peat moss-heavy blend will corrode these beds faster. Therefore, unless you’re ok with replacing them after less than a decade, it would be better to go with a more sustainable material. Constructing a bed from repurposed galvanized steel can be a chore sometimes and may require more than one person to execute.
It’s worth noting that corten steel beds can also deteriorate and stain the surface they are placed on. However, this doesn’t cause any harm to the surrounding environment, nor is the staining irreversible. You can place the corten planter or bed on a draining tray, or divert the runoff away from your concrete surface. Pressure washing the concrete every now and then should also remove the staining.
Before we get into the pros and cons of wooden raised beds, let’s discuss types of wood. Hard wood holds up longer than softer or composite wood. Most wooden raised bed guides recommend using cedar lumber that has been treated to withstand the elements. You can also use oak, pine, fir, cypress, and redwood to build beds. Factors like cost and availability will come into play when you decide what to build.
Advantages of Gardening in a Wooden Raised Bed
Wood is sometimes a cheaper and more aesthetically pleasing choice for a natural garden setting. Especially if you’ve located a good source of non-pressure treated wood that is made of high-quality materials like douglas fir, cedar, or redwood, both you and the garden benefit. Raw materials that don’t contain chemicals can even be reincorporated into other projects after you’re done using them as raised beds.
Upcycled wood isn’t hard to find for building a raised bed. The modularity involved when you build a raised bed out of wood means backyard gardeners have complete creative control. Adding soil annually can be as difficult or as easy as the design allows.
Disadvantages Associated With Wooden Beds
Treated wood may hold up for longer, but untreated wood could be better for a food crop garden. There are plenty of stains and sealers out there that are designed to be used to fortify wood garden bed materials. However, there are plenty of raised bed kits that contain treated wood that might not be safe for growing food.
Pressure treatments are sometimes advertised as safe for garden beds, but that’s not always the case. Avoid those treated with chromated copper arsenate, as they leach into the garden bed and into the area where you grow food. Untreated wood may be an easier option to build a raised bed overall, but this means your wood will rot faster than a sealed or pressure-treated bed.
So while wood is one of the best materials for raised beds, finding the right rot-resistant woods can be difficult. Acquiring wood at an affordable price is also difficult these days. If you choose to use recycled wood, you could run into rot issues even faster than you would with new pressure-treated wood. The difficulty of building the bed is high compared to other materials too.
Brick and Concrete Beds
Reused brick, cinder block, concrete block, and concrete planters are all viable options as raised bed materials. You can lay bricks in the appropriate fashion, and have a raised bed in no time. You can go one step further and mortar or cement the beds together. There are even kits that come with wood paneling and concrete corners.
Brick, Cinder Blocks, or Concrete Bed Advantages
Bricks and concrete blocks are very easy to find. People get rid of them all the time on resale websites, and they’re widely available in big box stores. You can easily design whatever size and shape of raised bed you want too. When it comes to modular building materials, you’re working with one of the lowest design difficulties with bricks and blocks.
One really awesome thing about brick is that it withstands cold best of all the materials we mention here. It holds the most heat, especially when you work with a good quality brick. Older, antique bricks tend to be made of stronger materials, standing up to the elements longer. This means it’s possible to work with reusable materials when you choose bricks.
Disadvantages of Brick or Cement Blocks as Raised Garden Beds
One of the main concerns involved with cement blocks and cinder blocks is that concrete can be toxic. That means not only could the concrete leach into the surrounding soil of your front yard garden, it can also leach chemicals into food crops. Concrete blocks of all kinds are made with fly ash, which is an aggregate used in their manufacture. This aggregate contains heavy metals and other materials unsuitable for growing food crops or plants in general.
Not only could they be toxic, but all of the materials in this section are heavy and may be difficult for one person to set up by themselves. For those who use equipment to be mobile in their gardens, this may not even be an option due to the heft of each brick or cinder block.
Poor-quality bricks can crack easily in cold, wet environments. So can concrete, cinder block, or cement materials. This issue thwarts their rot-resistant capabilities. While they won’t rot like cedar or redwood, they may not last as long in certain environments, meaning the effort you made could be thwarted within a couple of years.
Plastic and Resin Beds
Plastic and resin beds have become much more common in the home gardening sphere in recent years. It’s very easy to find either material bed in big box stores and online shopping sites. Some come in kits, and others come fully set up. Both plastic and resin are among the most popular materials used for raised beds today.
Benefits of Plastic and Resin Beds
We’ve mentioned the convenience factor for these types of beds. With modular and above-ground options available, you can make growing even more convenient. Having the option to garden above the soil line in a raised bed on legs is great for people who have trouble bending and reaching an in-ground bed.
Aside from that, plastic and resin are some of the most durable materials out there. You won’t have to deal with replacing or conducting maintenance of your beds during the growing season.
Producers of these beds tend to understand that human health and safety is important, so many of the plastic or resin beds on the market today are BPA-free and are made from polyethylene that doesn’t leach into the soil. Several manufacturers advertise that the beds can be recycled when you finish using them.
Plastic and Resin Pitfalls
While you won’t have to repair broken bed walls, unless you are working with a specifically BPA-free material, some upcycled and reused materials can actually contain BPA. That means there is potential for BPA leaching into the soil and into the food you’re growing. Furthermore, plastics may be advertised as recyclable, but the truth of that lies in the resources of your municipality’s recycling system.
Another issue that can arise with plastic is because it’s so durable, it retains moisture really well – sometimes too well. Therefore, for those plants that rely on consistent drainage to thrive, plastic is not a place they’re likely to survive unless there are sizable enough drainage holes.
Fabric Beds and Grow Bags
Fabric beds and large grow bags are highly popular materials for gardening these days. They have a lot of advantages, but a few issues that gardeners might not consider when they buy grow bags or fabric beds.
We have an excellent fabric raised bed in our shop by Grassroots. This modular bed can be assembled in different configurations and can fit in different spatial situations. Along those same lines, there are multiple sizes of Root Pouch grow bags that give you options when you’re building a new garden or adding to an existing garden. With sizes that range from 5 gallon to 100 gallon, these grow bags are suited to any garden.
Fabric Raised Bed Advantages
Both fabric options we’re discussing here are some of the cheapest and most modular materials you can use for a garden. They work well in both settings with a lot of space, and in situations where growers only have a small balcony to work with. They don’t stain concrete surfaces, and most plants grow well within them.
People who use equipment for mobility will also grow with ease when it comes to standard 5 and 10-gallon grow bags. They are much easier to move around than large raised beds, and they’re smaller. That means plants are happier, too, as the simplicity of moving a grow bag indoors for winter or out of the sun is what makes them awesome. And both options air prune roots, making above-ground growth healthier.
Disadvantages of Fabric Raised Beds
If you’re working with very large fabric beds or grow bags, they’re actually not that easy to move around. They also don’t hold moisture as easily as any of the other materials on this list. I find I have to water my grow bags much more than I do my wooden raised bed or my Birdies bed. If you live somewhere that has hot or cold weather, you might have to supplement with a heavy layer of mulch to ensure your beds don’t dry out.
Another issue with these beds is they need to be laid on cardboard or some other liner if your garden doesn’t have areas without grass or weeds. You may also find yourself adding more soil and organic matter to your raised beds more often due to a lack of moisture retention and depletion of nutrients.
Natural Stone Beds
Natural stones are another option for building your very own above-ground beds. These could be stones you find on your property or flagstone and mossy rocks you acquired from a hardscaping materials distributor. Let’s discuss the benefits and pitfalls of these.
Stone Bed Benefits
When it comes to natural stones (whether you’ve sourced them within your garden space or acquired them elsewhere), you’re working with one of the most natural materials out there. As they break down, they provide essential micronutrients to the soil.
Locally-sourced stones are the most environmentally friendly materials on this list. Just like cement blocks or bricks, there’s a lot of modular potential in them too. You can place them directly on the ground or on landscape fabric if you need to. If you’re sourcing from your own property, they’re cheap as well.
Stone Bed Disadvantages
Much like concrete and brick blocks, you’ll have to move these around, and they can get heavy. If they’re not sourced locally, they can be expensive and difficult to transport. Even though they have a lot of modular capability, they could be thick and disadvantageous to those who are trying to maximize space. They could also fall over if they’re stacked precariously on loose soil. This makes maintenance a consistent concern.
Reclaimed and Miscellaneous Materials
Now that we’ve examined some of the most commonly used materials for above-ground beds, let’s discuss miscellaneous supplies you can gather for your beds.
Pallets are a common reuse material employed in raised bed building – most commonly in vertical gardening. Having the option and access to pallets is great, but most pallet producers treat their pallets with a chemical called methyl bromide, which is highly toxic to humans. Ensure you know the origin of the pallets before you acquire them; that way, you don’t poison yourself.
Railroad ties are a hefty and substantial material a lot of people will reuse to build beds. Most railroad ties are a form of pressure-treated wood, and many are coated with creosote as a way to seal the ties and prevent rot. As we’ve discussed, pressure treatment lends toxicity to the garden, and creosote does too. It’s very dangerous to use ties that haven’t been worn out for many years.
Fence posts can be reused too. As long as they are sealed with food-grade sealers, they are perfectly ok for beds. Beds constructed of sticks/branches and any combination of either is great. They can be difficult to design, but especially if they’re sourced in the area where the garden is, you’re working with native ecology and a local microbiome which benefits plants greatly.
Adobe is a great material for making beds, mostly because of its thermal capabilities. These are best suited for dry and arid climates, as climates that are very wet will deteriorate the beds quickly. At the very least, high humidity and even no rain will create a situation where the beds erode much more quickly than other ones.
Wine and whiskey barrels repurposed as large planters are an excellent way to garden above ground. Even though the wood fiber contains alcohol, it doesn’t leach into soil in a way that damages your plants. If you have a good source for these, they can be affordable, but if you don’t, they may be expensive.
Old reclaimed tires are another round option for above-ground beds. There’s no need to design or build anything; just add soil. However, tires contain a lot of toxins that may or may not leach into soil. There’s very little evidence to suggest one way or the other. Therefore, proceed with caution.
Hay bales are another raised bed garden material that is great, because all it takes is placement, filling with your soil and plants, and voila! You’ve got a raised bed. There are few downsides to hay bale beds, but look out for weed seeds in your bales, and know that you’ll have to replace them over the course of 2 to 4 years.
Frequently Asked Questions
Q: What is the best material to make a raised garden bed?
A: High-quality galvanized raised beds with a coating or a long-lasting wood like cedar are best.
Q: What is the cheapest material to use for raised garden beds?
A: Concrete blocks or cinder blocks are the cheapest raised garden bed materials available.
Q: What do I put on the bottom of a raised garden bed?
A: Unless you’re working on a slope or on concrete, you don’t need to line the bottom of the bed. Leaving it open to the native soil allows the soil microbiology to freely spread through your raised bed soil.
Q: What should raised beds be made of?
A: Use the raised garden bed materials that work best for your garden’s needs. Consider your financial, physical, and spatial capabilities, and go from there!
Q: Is it OK to use treated lumber for raised garden beds?
A: While many people do, it’s not recommended, especially if you’re growing food. If you must use pressure-treated lumber, place a liner between the raised bed and the soil within so the chemicals don’t leach in.
Q: Is wood or metal better for raised garden beds?
A: It depends on your situation, but metal is much easier to work with, especially if you have a kit to build your bed out of.
Q: How do you make a raised garden bed that won’t rot?
A: Use non-porous materials that aren’t subject to rot, like metal or stone. Remember that stone, brick, or concrete have rough surfaces that provide a good environment for mosses to develop.
Q: How deep should a raised garden bed be?
A: 8 inches is as shallow as you should go. However, depending on the raised garden bed materials that you’re using, you can increase the height. A tall raised garden bed can be a lifesaver for anyone who’s mobility-challenged!