How To Build A Raised Garden With Cinder Blocks

There's a lot of different ways to build a raised garden. Some people use lumber, some use various types of stone, and some don't use any frame at all. But a cinder block garden is the cheapest and easiest way to build your own raised garden. In fact, you can get it all done in a single afternoon.

Follow these steps to learn how to build your own cinder block garden, and what you need to watch out for if you do.

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Why Build a Cinder Block Garden?

I used to wonder, what's the point of planting a garden directly on top of existing soil in your yard? Why not just till a garden into your yard and plant in that? Well, as it turns out, there are quite a few good reasons.

Depending on where you live, there's a pretty good chance the soil in your backyard or gardening space doesn't have the required nutrients to sustain a garden for very long. It may also be rocky, have lots of tree roots, high lead content, or other pollutants. The time, cost, and labor it would take to dig through all that soil, remove any contaminated, and then refill it with new soil wouldn't be worth it.

Also, building a raised bed with cinder blocks will reduce the number of weeds in your garden, since the bed has fresh, new soil, and is protected from invasive weeds by the cinder blocks.

What's a Cinder Block?

For my whole life, these rectangular stone blocks have always been called "cinder blocks". And I used to think most other people in North America call them that as well. Well, it turns out that actual cinder blocks (made with cinder) have become less common for a pretty good reason, and have been replaced by concrete blocks.

Cinder, also known as fly ash, is the by-product of coal-burning power plants. It contains dozens of dangerous heavy metals and contaminants, including lead, arsenic, mercury, and others. For decades, companies produced cinder blocks by using fly ash as an aggregate replacement for sand traditionally used in making concrete. By using this ash instead of heavier materials, the blocks were much lighter and easier to use.

Unfortunately, these traditional cinder blocks shouldn't be used to make a cinder block garden if your gardening goals include growing vegetables to secure your food supply and feed your family. There have been some recent studies and concerns raised about the harmful chemicals and toxins leaching from the cinder into the soil, eventually making it into your veggies. Just to be safe, it'd be best to use concrete blocks for your low-cost, low-maintenance garden.

Concrete Blocks

You've most likely been calling concrete blocks "cinder blocks" mistakenly without even knowing there was a difference. Well, it turns out lightweight "cinder blocks" don't have the best structural integrity. They also have the potential to contain poisonous toxins. So they decided to just make concrete blocks without cinder, and use sand instead.

The general public never noticed they changed the recipe though, cause they look almost identical. But, they weigh more and have none of the dangerous toxins in cinder.

Before you buy or find blocks for free, double-check if they've been made with cinder or not. Although cinder blocks have become rarer, they are still produced in some areas of the United States.

Planning Your Cinder Block Garden

Before you start moving cinder blocks around, you need to plan your garden. These blocks weigh between 30 - 40 pounds, so you want to make sure you know where it goes, and only move it once!

You likely already know where you want your backyard garden, so measure out the exact size that you want your raised garden to be. Keep in mind not to make your garden too wide, or you'll have problems trying to reach all of the plants without walking through the garden bed. If you don't know what size would be best, use one of these free garden planners to help out.

Once you know how long and wide you want it to be, calculate how many blocks you will need. Concrete blocks come in a variety of sizes, but the standard 8x8x16 size works perfectly for gardens. They cost between $1.50 - $2 per block at Home Depot.

If you plan on building more than one raised garden, don't forget to space them out properly. Make sure you have ample space to walk between the beds and tend to each garden. If you have a lawn, the width of your lawnmower deck should be the minimum distance between your gardens.

You should also decide whether you want your cinder block garden to be 1 or 2 rows high. A second-row adds more depth to your garden but will double your cinder block cost. I suggest starting with 1 row, and if you don't like it you can always add a second next year.

How to Build a Cinder Block Garden

With a paint marker or marking string, outline the footprint of your new garden. By marking the straight edges, you'll be able to keep your block walls straight as you build them.

The surface under your garden won't be perfectly flat. Because of this, you'll have to do a little leveling of the blocks as you go. You can lay the blocks directly onto the grass below, but they will eventually settle and become uneven over time. To avoid this, either dig the grass out and use a spade to even out the surface, or use sand to create a level surface under the blocks.

Begin by laying the blocks on their side (the hollow side facing up) in a row down each length of the outline to build your walls. It's very simple. Depending on the style of concrete block you have, they may even have little joints on each end to fit together like a puzzle. Use a small level to check each block as you go, and adjust its base accordingly.

Once your blocks have been laid, you need to line the inside of the garden with a weed barrier before adding soil. This liner will keep the grass/weeds below the garden from growing up through the new soil. The cheapest solutions include using painter's paper, cardboard, or newspaper. Anything biodegradable that won't harm you or anything else will be fine.

Finally, add your soil. Use high-grade soil with a good amount of homemade compost. Fill in the hollow parts of the blocks as well to add more growing space for herbs or flowers around the perimeter of your garden. After a few weeks, the soil will settle in some areas, so you'll need to do some spot filling.

Want the printable instructions? Here you go!

Materials

Concrete blocks (aka cinder blocks)
Garden fabric/liner
Garden Soil
Flowers or Vegetable seedlings or seeds for planting

Tools

Paint marker or marking line
Trowel
Craft knife or scissors
Level
Spade

Instructions

To start, plan your garden dimensions and purpose based on your available backyard garden space.
With a paint marker or marking string, outline the footprint of your new garden.
Dig down one to two inches with a spade.
Lay a block on its side (holes up) in the dug-out area.
Level each block as you place it.
Line the interior of each block with gardening fabric.
Add soil.
Plant your flowers or vegetables.

What To Watch Out For

If you have concerns about the possibility of your blocks containing cinder, use a gardening grade plastic liner instead of paper. Wrap the liner up the insides of the blocks before adding your soil. This will create a barrier of separation between the blocks and your soil to protect against any contamination.

Ideally, you'll find your concrete blocks for free. People always seem to have extra concrete blocks around that they want to get rid of. And while you're at it, look for pallets to build a pallet fence for free.

Just make sure that if you do find some free blocks, that they're all the same size and style. You could build a mismatched wall if you really want, but it won't hold together well and it'll likely be an eyesore. Just get all matching blocks.

Building a cinder block garden gives you a chance to build a unique raised bed garden without spending a bunch of money and hours building a custom wood one. Other than a bit of a workout carrying all those blocks, it's not difficult and can be accomplished in an afternoon. Find your optimal garden space and start planning your new homestead project.

More Resources for Building a Cinder Block Raised Garden

University of Missouri - Raised Bed Gardening
University of Minnesota - Raised Bed Gardens
University of Louisville - Safe Container Gardening
University of Florida - How to Build a Raised Bed Garden
University of Maryland - Materials for Building Raised Beds

Interested in more gardening related posts from An Off Grid Life? Check out the links below.

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