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Can you Build RAISED GARDEN BEDS out of Cinder Blocks?
Pros, Cons, and other options
I don't want to be Mr. Know-it-all here but technically, "CINDER BLOCKS" haven't been commonly manufactured in years and what we are referring to is actually known as "concrete blocks".
Can you Build Raised bed gardens with Concrete blocks?
Yes, you can build raised garden beds out of concrete blocks. Modern concrete block doesn't use cinders (coal waste) as the aggregate so they are more durable, and don't leach harsh chemicals into the soil. They are also less costly per foot than wood in 2022.
What is the difference between Cinder Blocks and Concrete Blocks?
Traditional cinder blocks had actual cinder as the aggregate (aka bottom ash coal waste from burning coal) and they are lighter and more brittle. They also don't last nearly as long as modern-day concrete blocks. They were made that way because coal waste was plentiful and worked well enough as an aggregate and the bricks we lighter than normal concrete.
Most blocks that look like the blocks pictured above are called concrete blocks because they contain stone or sand as the aggregate which makes them heavier and more durable.
Benefits of using Concrete Blocks for Raised Garden Beds
First and foremost, the elephant in the room...
It's 2022 and lumber prices are at it again. Unless you mill the wood yourself, concrete blocks are going to be better choice from a price perspective no matter who you are. If I bought wood from the hardware store at these crazy prices (which I don't) I'd have a really hard time burying it in a bunch of soil.
You don't have to worry about rotting and replacing boards with these blocks. They won't shift or warp over time like wood.
Set it and forget it basically. The concrete blocks are modular so they can be put together like big legos without nails and screws. This allows you to stack them as high as you want and as long or wide. You can basically make any shape as long as it's a rectangle.
Blocks can be 8 inches tall by 16 inches long and 4 or 8 inches thick. They weigh between 19 and 40 pounds. So these are not only more durable and cheaper than wood, they offer more girth to make your garden beds firm.
These concrete blocks are everywhere and if you are a resourceful person, you can scan Craigslist, Facebook marketplace, Letgo app, as well as friends and family to find some for free. These blocks are everywhere because they are a very common building material and man times leftover from old projects.
The only obvious downside is that you may not want to use some dirty old used bricks unless you know where they came from. Also, as I mentioned earlier, some of these really old bricks may have bottom ash as the aggregate and that can be toxic. The easiest way to tell if that is the case is that the brick will feel really light since it's not made with sand or gravel.
You can also use the tiny holes as mini planters too, which my wife really likes for flowers and other things to attract pollinators or keep pests away.
Here are a few ways to make Concrete Block Raised Garden Beds look good:
Level your Gardening Site:
You'll love going into your garden if everything is neat and level. Make sure everything lines up straight on the side sand on the top so some blocks aren't higher or lower than others. This is the most important for visually appealing raised garden beds!
Toppers: Use nice wood 2X8 or Concrete toppers to cover the holes
Paint: You can paint the concrete to give it a cleaner or unique look. I would do this before planting anything or putting dirt in it and I would use a roller or sprayer with exterior paint.
Use Pillar Blocks for Corners: Pillar blocks are the corner blocks that also add curb appeal and are very aesthetically pleasing.
Cons of using Concrete Blocks for Raised Garden Beds
Concrete Blocks are Heavy
If you are a weight lifter, these might be easy to use.
think about this. A common garden bed is 4 feet by 8 feet. If these blocks are 16 inches long, you'd need 18 for each garden bed. That's over 760 lbs if each block you get weighs 40lbs. You better have a decent truck to haul these bad boys.
You (should) Level the Gardening Site:
You need to make sure the ground is level or else could look like trash. I might be nitpicking here, but as someone who has done a ton of landscaping and retaining walls, leveling dirt, rocks, mud, and roots in can be a pain in the neck.
Wood is more forgiving in this sense because it's all nailed together as one piece. So if it's a little off, it can be adjusted after installing or may not be as noticeable. With concrete blocks, you have to get it right because once these are filled with dirt and stacked on top of each other they will be impossible to move. It will literally weigh hundreds of pounds.
Since these blocks having holes in them, it is the perfect little home for small mice and voles. I recently had one of my dogs flip one of these concrete blocks over to reveal mice living in the opening...not cool.
A good way to prevent that is by making sure you put metal wire or fencing flat on the ground under the blocks to prevent anything from burrowing underneath along with a topper to cover the hole on both sides.
Some people hate the way concrete block garden beds look. It looks industrial and almost cheap or out of place. Personally, I don't care.
Is it Dangerous to use concrete blocks for Raised Garden beds?
No. Many people wonder is the concrete can leach some of the ingredients into the soil, thus into the food. There has been a study by Oregon State University according to some other sites (though, I can't find it for the life of me) that the lime used to make the concrete blocks can leach into the soil over time (how long, I don't know). This increases the acidity of the soil (side note, higher acidity is great for blueberries) but is not harmful to humans.
These modern concrete blocks are made up of sand, gravel, water, and cement. I put some cement ingredients below because I wanted to know, so figured ya'll might.
Where Can I Buy Concrete Blocks?
Below are the prices that I found for two common concrete blocks at three common hardware stores:
What can I say? Save big money at Menaaaaaards.
How should I secure the Concrete Blocks?
Securing the concrete blocks can be done in a few ways.
Put 4X4 most into the opening of the blocks on the corners and bury it in the ground. This will make it extra secure and easier for leveling
Construction adhesive on the sides and or tops where two blocks meet. This will give it added structure.
Rebar can also be used to give it structural integrity along the walls of the bed.
Garden Beds can be made out of modern concrete blocks but avoid the old-fashioned cinder blocks due to their lack of tensile strength and toxic material.
Concrete blocks are more cost-effective but can take a little more elbow grease to get it exactly how you want it.