Are you interested in container gardening? Are you wondering the best way to build a raised bed to create a little garden space for all your herb and vegetable needs? If you’re looking for something a little more personalized than the wood boxes you can buy in the store, this post is for you. I’m going to show you how to build a vegetable garden out of concrete cinder blocks! These cinder block beds can be arranged in all different shapes and sizes to work in whatever garden area you have at home. And, if you aren’t sure you love the look of the concrete block formation, I’ve got a great hack to make your bed look solid and modern. Let me show you exactly how I made mine!
This post contains affiliate links. I make a small commission if you choose to buy any of the products I’m endorsing. The opinions in this post are my own, and I really do love all the tools and products I’m using for this project!
As a passionate gardener, I’m always looking for ways to enhance my vegetable garden Lately, I’ve been considering using concrete for things like raised beds, paths and planters. Concrete offers durability and structure But is it safe for my veggies?
I decided to dig into the details to find out, Here’s what I learned about using concrete in vegetable gardens
The Benefits of Concrete
Concrete offers some useful qualities for vegetable gardens:
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Durability: Concrete holds up well to weather, pests and heavy use. It can last for decades if properly maintained.
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Structure: Concrete provides a solid foundation for raised beds, trellises and other structures. This support helps plants grow upright and tall.
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Weed Prevention: Concrete paths and borders block weeds from taking root and encroaching on planting beds. Less weeding means more time enjoying your garden!
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Drainage: Concrete does not absorb water. This allows excess moisture to drain away, preventing soggy soil.
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Pest Control: Concrete creates a barrier to burrowing pests like gophers. It also doesn’t harbor wood-damaging organisms.
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Appearance: Concrete has a clean, modern aesthetic. It defines neat beds and lines in the landscape.
The Potential Risks
However, concrete also comes with some potential downsides:
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Alkalinity: The lime content in concrete leaches into soil, raising the pH. Most veggies thrive in slightly acidic soil. High alkalinity can inhibit nutrient absorption.
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Compaction: Concrete resting directly on soil can compact it over time. Dense soil prevents proper drainage and root growth.
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Heat Retention: Concrete absorbs heat from the sun and can transfer it to the soil. This may damage plant roots or alter soil ecology.
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Water Runoff: Impervious concrete increases surface runoff, leading to erosion and nutrient loss. Permeable alternatives allow water to soak into planting beds.
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Toxins: Concrete can leach toxic substances like chromium, selenium and arsenic. However, modern concrete mixes contain fewer harmful ingredients.
Best Practices for Safe Use
With care, concrete can be integrated into vegetable gardens safely:
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Pick non-toxic mixes – Opt for concrete without fly ash or slag, which can leach heavy metals. Use mixes designed for gardening.
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Create a barrier – Line concrete beds with landscape fabric to block contact with soil. Or, elevate beds over concrete paths or footings.
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Seal regularly – Seal concrete annually with a non-toxic sealer to prevent leaching. Reapply after 5 years.
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Check the pH – Test soil pH around concrete periodically and amend as needed to maintain optimal levels.
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Ensure drainage – Incorporate drainage channels or gravel layers under concrete to prevent pooling water.
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Limit direct sun – Use shade structures or position beds to limit direct afternoon sun on concrete. This prevents overheating.
Practical Tips and Alternatives
With smart practices, it’s possible to incorporate concrete safely. But you may prefer to limit its use or avoid it altogether. Some great alternatives include:
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Wood – Cedar, redwood and composite lumber make attractive raised beds. Opt for naturally rot-resistant woods.
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Stone – Use rubble, bricks, pavers or boulders for paths, walls and edging. Granite works well.
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Tiles – Ceramic, porcelain or terra cotta tiles add charm and structure without leaching.
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Gravel – For foot paths, use pea gravel or crushed granite. Leave planting areas uncovered.
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Landscape fabric – Line beds and block weeds without chemicals. Use pins to hold it in place.
The Bottom Line
It is possible to use concrete safely in vegetable gardens with careful design choices. But risks do exist, so consider your specific needs. If you opt to use concrete, take steps to protect your plants from potential negative impacts. With smart practices, you can unlock the benefits of concrete while keeping your garden thriving.
How to lay your cinder blocks for a raised garden bed
So, once you have put down your gravel and sand mixture, it’s time to lay the first block! This block MUST be level or your entire garden bed will be off, so take the time to get it right. Lay the block down where you want it to sit and put your level on top. The air bubble needs to be in the center of both the vertical and horizontal vials. Once it is level, place the next block down next to it. Ensure it is really close, as you don’t want any gaps between your blocks. As soon as I put that block down next to the first one I could see it was lower at the back corner. I didn’t even need a level to see that! So, I built up that corner by adding a bit more gravel under it and then trying again.
It was so close!
Just a little bit high. Before I took the block out again and started removing gravel, I hit it with my mallet first. That corner was now level but it was a bit high on the opposite corner now. So, I moved the block and took a bit of gravel out from where it was high. As you can see, leveling this first layer of blocks took some time. But block by block I was able to get every single one leveled out in a straight line. It is just a bit of a process.
Do you remember that I purchased a single square block as well as the rectangular ones? You don’t want to line up the blocks perfectly with one another. This would have made a single line of weakness where the blocks all butted up against each other. Instead, I put a square block in the lineup in the second position so the ends were staggered. I also put the first block down in one direction and the rest that followed were the opposite direction.
These tricks are something easy you can do to increase the stability of your final structure.
Once the base layer of blocks was down and leveled out, I made it even stronger by adding Loctite construction adhesive. I simply removed the blocks one at a time from their set position, added the adhesive to the ends, and then put them back in place. And of course, after I put each block back in place I checked that it was level again, making little adjustments here and there with my trusty mallet. I highly recommend this step, as it will make your garden boxes into one solid piece and help prevent your blocks from settling separately over time.
How to Build a Raised Garden Bed with Concrete Blocks – FAQs!
Let’s get these questions out of the way first!
How to Go From Concrete Slab to Productive Raised Bed Garden in Just A Few Months!
FAQ
Is concrete safe for a vegetable garden?
Concrete blocks are perfectly safe to use around raised garden beds whether you plant an edible garden, shrubs or flowers.
Does concrete leach chemicals into soil?
Is cement safe for garden beds?
Concrete, Cement, and Soil Chemistry
In brief: concrete curing isn’t harmful to your plants or your soil necessarily, but it does affect the chemistry of the soil around it. The curing process can alter soil pH, increasing its alkalinity in ways that may not be good for some plants.
What is the safest material for a raised garden bed?
Composite wood is rot-resistant and more durable than natural wood. Concrete blocks or bricks: These building materials can be arranged to form the walls of your raised bed. They are safe, sturdy, and long-lasting. Stone: Natural stone can be a beautiful, durable, and safe choice for a raised bed.