DIY Cement Garden Beds

These are actually concrete block garden beds covered in surface bonding cement, but that was too much of a mouthful for a title. Ha!

I wanted to plant some berry plants along our fence line, parallel to our septic lines, but I didn’t want well….poop berries or a ruined septic system, so I needed to come up with a way to contain the berries and keep them the requisite 10 feet away.

Concrete block beds seemed like a good choice, but I didn’t want them to look like concrete blocks. I found this QuikWall product from Quikrete that not only pretties up the blocks a bit but also literally cements them together into a sturdy, permanent structure. It was all a bit of an experiment because the only tutorials I could find when I started this project last year, were for small walls. It made sense though that if this stuff can make walls sturdy then it could handle a foot tall garden bed…And it did!

MATERIALS

• concrete blocks*
• concrete block caps*
• QuikWall surface bonding cement made by Quikrete*
• finishing trowel
• drill and drill mixer attachment
• garden hose
• gravel plus minus**
• hand tamper
• level (preferably a long level that’s at least 2 feet)
• shovel/pick axe
• optional: patio paint or garage flooring epoxy paint and heavy duty rough texture paint brush

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Material Notes:

*I used 19 concrete blocks, 19 caps, and about 1.5 bags of surface bonding cement per bed. I found my concrete blocks from Home Depot for $1.45 a piece.

*I wasn’t able to find QuikWall at my local big box store, although I think some locations carry it, so I ordered it through my local tile shop.

**You want to use a gravel that can be compacted like what is used in driveways. I used granite gravel with “minus” or gravel dust that gets in between the rocks and helps it compact so that when you walk on it, you don’t sink. Do not use pebble gravel or any gravel that has smooth rocks. This will not compact and will create an unsteady base for your blocks.

VIDEO TUTORIAL

I put together a video tutorial below that documents what I did. It shows you how the mixture looks being spread on, which is probably the most helpful part. I still recommend reading the written tutorial because there are lot of details that I didn’t include because it would have made the video too long.

***PLEASE NOTE***

I sometimes use the word “cinder” in place of “concrete” when describing these concrete blocks. To a lay person, these terms are often used interchangeably and I wanted to use terms that would be easily recognized. I also used them interchangeably, not knowing there was an important difference, until I shared this post.

Older cinder blocks are made with fly ash and contain chemicals that can be harmful to your health. Newer concrete blocks that you can get at the hardware store do not contain fly ash. They are made of water, stone, and concrete and they are safe for food. If you are using these beds to grow food, please use new concrete blocks.

WRITTEN TUTORIAL

Step One: Determine Location and Size

My beds used 19 concrete blocks and 19 caps each which created a bed about 3.5 feet by 10 feet (39.25 x 125.75 inches). The actually growing space is more like 2 x 9 ft. though because the blocks are about 8 inches wide.

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The concrete blocks are 8 inches tall and the cap blocks are 4 inches, which makes this bed about a foot tall.

Step Two: Prep the area and remove the grass.

Remove any grass or weeds from the area and start leveling out the ground if you’re on an incline. The gravel that will be added in the next step will help with the leveling a little bit too, so don’t worry if it’s not perfectly level at this point.

If you have rocky soil like I do, then I highly recommend using a pick axe rather than a shovel. It will save you so much time and frustration.

Step Three: Add a gravel base.

Lay at least 1-2 inches of gravel underneath where the blocks will go, compacting it with a hand tamper and leveling it as you go. For some of my beds on more of an incline, I had to add more like 3-4 inches of gravel.

You will likely have to adjust the amount of gravel you need in the next step, so you don’t have to get too picky about how precisely it’s leveled just yet.

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Step Four: Add concrete blocks.

Now is the time to get picky about leveling. As you add your concrete blocks, ensure that they are perfectly level. You may have to add or subtract gravel to get this just right. I also recommend re-compacting any disturbed gravel, which I didn’t always do and ended up regretting later (I’ll explain at the end).

This step takes the longest, but it’s very important to get right as it determines the stability of the beds and makes the next steps much easier.

Step Five: Add cap blocks.

This part is fun. Just add the cap blocks, ensuring the placement is staggered with the concrete blocks. It goes by super fast because you already did the hard work of leveling the first layer!

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Step Six: Add the QuikWall surface bonding cement.

Spray the concrete blocks down with water to help the surface bonding cement adhere to it. You will need to re-wet them as you go, especially if the weather is hot and sunny.

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Mix the surface bonding cement according to package directions until you get a mixture that is the consistency of a thick pea soup. Then you spread it on like you’re frosting a giant cake. You want it to be thin enough to spread to about 1/8 -1/4 inch on the blocks. If you are working with it on a hot day, you will want to start with a little bit thinner mixture because it will thicken up quickly. If it starts to get too thick to spread thinly, you can add water to maintain the proper consistency.

Which leads me to a note about cement dye: I wanted my beds to be black, so I also added a cement dye to the water before mixing it with the QuikWall. Not only did it not give me as saturated a color as I was hoping for, it was also hard to keep consistent if I needed to add water to the mixture as I worked. So, if you are a novice like me and want a color other than gray cement, plan on painting them and skip the dye.

Spread a thin layer 1/8 inch to 1/4 inch thick of QuikWall on the outside, tops, and inside of the blocks. I mostly left the rugged troweled texture, but did smooth the corners and edges using a gloved hand.

Optional: Paint the garden beds.

Let it cure according to the package instructions before painting. I used patio and porch paint, but have since touched it up with garage epoxy flooring paint from my stenciled greenhouse flooring project. Use a brush made for exterior, rough surfaces.

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COLOR TIP: I should have known, but I found that black paint makes dirt and bird poop very obvious, so it needs to be cleaned and refreshed more often than white or a lighter color to stay looking nice. Dark paint can also heat up the soil in the bed. This is actually an advantageous thing in our cool climate, but may work against you if you live in a hot climate.

A YEAR LATER

I made these beds last year, but decided to wait to share my tutorial until I had used them for a year to see how they fared…remember this was an experiment.

A year later, two out of three look great! One has a couple of cracks I think where the ground settled over winter. This is why I recommend re-compacting any disturbed gravel in step three. The cracks are just cosmetic though and have not affected the integrity or stability of the bed which is the most important thing. If I get around to it, I may try patching it with some leftover surface bonding cement. Maybe. Ha!

I also decided to add another coat of black paint because it had gotten a bit hazy and dingy over winter and I wanted it to look fresh and new for this post. 😉

So far, they are doing a good job at keep the berries in check. We’ve had a few runners pop up outside the beds but we are able to easily mow it down when we cut the “grass.” I put that in quotes because it’s really weeds at this point. Ha!

Some things to consider:

After this post did well on Pinterest, I got a few questions, and a few comments that I thought I would address.

1. The color. If you live in a hot climate, black will not work for you and may cook your plants. Unpainted it may even do this as well…consider your climate. If you live in a cooler climate like mine, black or darker colors can work to your advantage. It will keep the soil warmer and help it warm up sooner. I will say that it is harder to keep looking clean though. Birds poop on the beds and it shows up really well. 😉 They get dusty looking in the summer when our lawn dies (which is a common practice in Washington state to help conserve water, but that’s another topic). I am considering repainting them a lighter color purely for aesthetic purposes. Just thought I would mention that.
2. Concrete blocks. As mentioned earlier, newer concrete blocks are safe to use with food. Do not use older “cinder” blocks as they contain chemicals that can be harmful.
3. Foundation. This is not a wall and nor should you use this tutorial to make anything taller than I did. If you do, you will need to consider a frost line foundation and using mortar between blocks.
4. The surface cement. It is meant to applied thinly. Please refer to product information from the manufacturer. It does not crumble, or chip, or fall apart. My beds are 2.5 years old and are holding up beautifully. They are super solid and I just created four more.