What material should I use to make a raised garden bed, do you want to know? Well, it depends on your personal preference, style, budget, climate and what materials work best for you. Let's explore options!
This article will cover the most common (and less common) materials used to make raised garden beds—including wood, metal, concrete, and more. We'll discuss things to consider when choosing a material, such as durability or safety, and the differences between various woods. Finally, don't miss our list of potential raised bed materials we recommend avoiding for organic gardening.
Common Materials for Building Raised Garden Beds
Wood, including hardwood or softwood options
Metal, such as corrugated metal or galvanized steel drums
Bricks, cinder blocks or concrete blocks
felled logs
pouring concrete
wine barrel
straw bales
Large natural stones, pebbles or stacked rock walls
Pallets, fence boards or other upcycled wood
Other miscellaneous containers or materials
Choosing the Best Materials for Garden Beds
In addition to the list above, you can create a raised garden bed with just about anything that will hold soil and plants! A kiddie pool, old tires, scrap wood found on the side of the road… the options seem endless. However, there are many factors to consider when deciding on the best material to use. Not all are created equal!
longevity
If you want them to last, choose a sturdy and durable material for your raised garden beds. After all, garden beds are subject to near-constant humidity, outdoor factors, and potential insects or pests such as termites. Plus, the soil is heavy - especially when it's wet! The more soil mass that is present (such as in large or raised garden beds), the greater the pressure on the bed walls. Thin wood can easily bend or rot in this condition. Even the best wood, concrete or metal beds will outlast wooden raised beds. We’ll discuss more about the best wood choices for building a loft bed below.
EDIT: Check out this newer article with 7 Ways to Make Your Wooden Raised Garden Bed Last as Long as Possible, with info on sealing, silicone, and more!
cost
Mostly (but not always!) cost is directly related to durability. Higher-cost, high-quality materials have the potential to last for decades or more. If you choose to save money up front and choose more affordable materials, you may be sacrificing the longevity of your loft bed. For example, a planter box made of recycled pallets or soft pine may not be half as long as a planter box made of high-quality wood. Also, large stones or concrete blocks cost more than straw bales, but can last a lifetime by comparison!
Now, that doesn't mean you have to spend a fortune building a raised garden bed! Depending on your situation, you may be more willing to give up a little longevity to keep your up-front costs down - especially if you're renting your current home, or just building a temporary garden space. There are also many ways to be resourceful and find many things. Visit your local Craigslist, Facebook marketplace, junkyard and more to find materials. Heck, if you have easy access to large felled logs, you can make an incredibly durable and affordable bed.
Finally, be sure to shop around and compare prices. For example, we are able to find a great deal of stone, block, gravel, bulk soil and mulch (and a wider variety of materials) at our locally owned landscape supply company. However, lumber has proven to be expensive at local stores and more affordable at larger hardware stores.
Safety
There are tons of creative and budget-friendly raised garden bed "hacks" out there - but I urge you to use some common sense! For example, I would think twice before using painted or treated salvaged wood to create garden beds for edible crops. Especially if the age and origin are unknown! Wood can be contaminated with toxic chemicals such as lead, arsenic or other heavy metals that can migrate (leaches) into soil and food. Even though modern pressure-treated wood is less toxic than the materials they used to make, I still recommend against using it.
I've seen people make garden beds using all kinds of upcycled materials: Styrofoam coolers (made of polystyrene, a suspected carcinogen) or old car ties (containing benzene, PAHs, Heavy metals and many others) substances that are harmful to human health). While I appreciate the effort to reuse items in the name of sustainability, I personally don't think it's worth the risk. See the sections below for a complete list of materials to avoid.
Types of wood used to make raised garden beds
cedar or redwood
Cedar and redwood are two of the best wood choices for building raised garden beds. They're all very durable, beautiful, and naturally resistant to moisture, corrosion, and even termites. The cost per person can vary greatly depending on where you live. We found that rosewood is more affordable on the west coast, while cedar is more readily available in the eastern United States and therefore less expensive.
Raised garden beds made from mahogany or cedar should last a decade or more! After all, the water storage tank used to be constructed of mahogany! Cedar and redwood are technically "softwood" woods, but both contain high levels of natural tannins (which repel rot and termites), which make them more durable than other softwoods. Due to its higher tannin content, rosewood is rumored to last several years longer than cedar—especially if you use heart rosewood.
When you browse the lumber department, you should see options for "common grade" rosewood or heart rosewood -- sometimes called architectural heart, "conheart," or heart B rosewood. We build our loft beds from heart mahogany, which is denser than regular grade or sapwood and therefore more durable.
Whenever possible, choose wood with FSC certification. The Forest Stewardship Council certifies wood from "responsibly managed forests that provide environmental, social and economic benefits".
Other wood options for loft beds
In general, hardwood lumber is denser, so it offers a higher level of durability and strength than softwood lumber. Examples of durable hardwood woods include teak, maple, beech, hemlock, walnut, locust, and oak. The barrels are made of oak, which both enhances the wine's flavor and provides incredible moisture resistance and longevity. We use wine barrels extensively in our garden as raised garden beds! Be sure to drill at least six drainage holes in the bottom using a 1/2" to 3/4" drill bit.
Hardwood trees, although strong, grow more slowly and are therefore far less common in construction than softwoods. Popular softwood woods include Douglas fir, pine, spruce, and juniper. These options are generally more affordable than mahogany or cedar, but are less durable. Raised garden beds made from these softwoods are known to last an average of 4 to 7 years (compared to 10 to 20 years for cedar or redwood), depending on your climate.
Another thing to consider is lumber size. The thickness of the planks also directly affects the lifespan of the garden bed. A raised garden bed made of 2" thick planks will outlast a bed made of 1" thick planks or ½" thick fence planks - by far! We used heart shaped mahogany 2×6 inch boards to build our loft bed.
Learn how we built our wood frame bed with this step-by-step tutorial (including video)! Or, check out some sturdy, easy-to-assemble loft bed kits here.
For our backyard garden (a few years ago, when we still had grass!) we built mahogany raised beds around the patio with trellis attached at the back that doubles as a chicken-proof fence as well. We also use wine barrels to grow tomatoes, turmeric, cannabis, herbs and more.
Should I seal my wooden garden bed?
This is another "it depends" situation! Redwood and cedar absolutely do not need a protective sealant, but may benefit in climates with high humidity or precipitation. If you choose to seal your wood garden beds, choose a nontoxic sealer such as GardenSeal or Hope's NaturalTungOil. Softer wood options will benefit more from the additional protection of the sealant. Follow the manufacturer's recommendations on how often to apply a new coat.
Personally, we don't seal our redwood garden beds, but we do live in a fairly dry climate! Sometimes foggy...but very dry. We also love the way the rosewood ages naturally, untouched. It starts out as a beautiful pink and turns into a slightly amber shade within a year before fading to a beautiful beach-barnwood grey. Cedar also ages gracefully over time, turning from a reddish brown to a silvery gray (unless a sealant is used regularly).
EDIT: Since moving to our new homestead and building our forever garden, we did choose to seal the interior of our new rosewood raised beds with several layers of garden seal to prolong their life.
Metal Raised Garden Bed
Metal raised garden beds are becoming more and more popular! They are modern, stylish and very durable. Unlike wood beds, metal beds don't rot over time, expand and contract with moisture, and don't require a lot of maintenance. That said, galvanized steel raised garden beds are a great choice for super humid climates! Some people may be concerned that a metal bed will heat up their soil, but that's nothing to worry about. Even if the metal feels warm to the touch, moist soil is a good buffer against temperature fluctuations. I know many hot climate gardeners who use metal raised garden beds, no problem.
There are many metal garden beds to choose from. You can make your own with corrugated sheet metal inside a wooden frame. Alternatively, turn a prefab metal container into a raised garden bed—like adding drainage holes to the bottom of a galvanized steel animal feed or sink.
Last but not least, there are tons of really cool metal garden bed kits out there! My friend Kevin just started selling some super durable and stylish Birdies garden bed kits, shown below. They can be made in a variety of shapes and sizes and were previously only available in Australia. (Use code "deannacat3" to save 5% on Birdies beds here!) Gardener's Supply Company also offers a range of premium galvanized steel options, like this modular bed set.
Whichever direction you go, be sure to use galvanized metal so the bed doesn't rust!
Are Galvanized Steel Garden Beds Safe?
Yes, well-made galvanized steel garden beds are totally safe to grow food! (Note the emphasis on well-made, so choose reputable and well-reviewed products!) Steel is an alloy of iron and carbon. Through the galvanizing process, the steel is coated with a layer of zinc, which effectively seals and prevents corrosion and rust. Large amounts of zinc are unlikely to seep into the soil from the coating. Zinc coatings require very acidic conditions and many, many years to decompose.
Even so, zinc is not a bad guy! Instead, zinc is a mineral that occurs naturally in the soil—and a micronutrient essential for plant growth! Plants rely on zinc to promote healthy root development, increase resistance to cold temperatures, and support other phytochemical processes such as chlorophyll formation. However, if your galvanized steel beds start to corrode noticeably on the inside, it's best to be safe and replace them.
Make Raised Garden Beds from Concrete, Brick or Cinder Blocks
As with garden beds made of metal, raised garden beds constructed of concrete pavers, cinder blocks or bricks have the potential to be extremely durable and strong. However, this category requires some considerations! The installation of concrete block garden beds requires a fair amount of commitment, especially if you use mortar or adhesive to hold them in place. They are heavy and create a more permanent design than other options, thus limiting your flexibility to make changes.
If you keep them fairly shallow, you can make garden beds using paver or blocks without adhesive (such as simply stacking blocks). However, if you're creating stronger units in areas prone to heavy rain or flooding, on slopes, or otherwise, you'll need to hold them in place. Interlocking blocks for mortarless wall systems can also be found.
We made a number of raised garden areas out of concrete blocks and fastened them with building concrete adhesive (the same way we made our concrete block greenhouse foundation). The adhesive may not be completely non-toxic, but we only used a small drop of glue deep between each piece. Also, these beds are mostly ornamental rather than edible. Be sure to let your adhesive dry and cure completely before adding soil!
Are concrete blocks or cinder blocks safe for gardening?
Fly ash is a common problem when building raised garden beds using paver, brick or cinder block materials. Fly ash is a masonry additive that contains heavy metals such as radium and arsenic and is often used in concrete products to increase durability. However, there is little scientific evidence whether these heavy metals readily seep into the surrounding soil. If you are concerned about this risk, buy materials from reputable sources where you can ask questions and check specifications for fly ash.
natural stone bed
In addition to concrete blocks, you can use natural stone such as cobblestone, flagstone, boulders, or other foraging rock materials to make long-lasting planting areas. Unlike concrete, there is no need to worry about chemical additives here. Natural stones and rocks can be stacked freely, or mortared/glued in place. Since natural rocks are not as uniform in shape and size as concrete blocks, construction requires more imagination and groping to piece them together. However, the end result will be more rustic, artistic and beautiful - and blend in perfectly with the natural garden setting!
Avoid using these materials for raised garden beds:
Rail link. Although they look a little funky, railway ties are treated with creosote - a "probable" human carcinogen. Creosote may also inhibit or harm plants growing nearby.
Recycled or reclaimed wood of unknown origin. As we've discussed before, be vigilant if you're not sure about the source, age or treatment of the wood. It may have been treated, stained or painted to introduce toxins into your garden.
Treated wood, or pressure-treated wood. This is up for discussion with some gardeners. Historically, pressure-treated wood was cured with an arsenic-based compound called chromated copper arsenate (CCA). The bad news is arsenic, with research showing that it can easily leach from treated wood into surrounding soil. The purpose is to make the rather cheap wood (i.e. pine) last longer in harsh environments. Although CCA was banned in 2003 and replaced by various less toxic copper-based chemicals, I personally still avoid treated wood. After all, the life expectancy of rosewood and cedar is actually several years longer than that of modern pressure-treated pine! So why choose chemically treated materials for your raised garden beds?
