Backyard Landscaping: Garden Retaining Wall

We had neglected our backyard long enough. It was time to do some landscaping. The first project was to build a short but long retaining wall along our back fence. The neighbors plot behind us is a couple of feet higher than ours. The fence splits the difference with the bottom acting as a retaining wall of sorts. But it was time to address this head on with something that looked good.

To save money we decided to DIY. I also knew this wasn’t going to be an easy job. Even though the wall is only around two feet tall, it is over 75 feet long. That’s a lot of dirt and materials. Plus we wanted something that looked substantial — so the block size would be large. This was going to be physically taxing, but with some help and wise pacing it was doable!



Our pile of Allen Block

The first decision: what materials to use? After some research we decided on Calstone Allen Block Classic. It had the large form factor we wanted, looked good, and Calstone is a local company — so availability was excellent in our area. The “Classic” was also cheaper than their tumbled “Europa”, and we liked the look.

Note that the largest block sizes were 60 to 65 pounds. This is a consideration when you do projects like this. Your going to be carrying those blocks all day long. Clearly I was going to need help. Thankfully my wife and son pitched in.


Base rock and gravel

In addition to the blocks themselves we needed baserock for the wall’s footing and gravel for filling the blocks. Plus a bag of sand to help with leveling blocks. Your block supplier should be able to help you with estimating the amount of materials you will need for your project. Also your block manufacturer should have installation instructions (Calstone has a pretty thorough installation guide).

And of course all this stuff had to be moved into the backyard. We borrowed a friend’s hand truck to move the blocks, and an extra wheelbarrow helped for the gravel and base rock.



Digging tools. The digging bar and soaker hose were very helpful.

Large landscaping projects require lots of water, sunscreen and advil!

Water, sunscreen and ibuprofen are key to a successful landscaping project.

No sophisticated tools here. Most of this job is digging, shoveling, leveling, compacting and hauling. I did need to cut some blocks for a  curved area at the end of the wall — for that I improvised with my circular saw, a masonry blade and the garden hose. You’ll also need some string and stakes for doing layout and I made a depth gauge that I’ll discuss later. And don’t forget lots of water, sunscreen and ibuprofen!



Test wall and soaker hose

The first thing we did was to decide on our layout — since that affects everything else. We decided we wanted the wall 20″ tall (including the top caps). We wanted the face of the wall to be 44″ from the fence which left a 32″ bed. For our blocks that meant a two course pattern plus the 4″ top cap plus the wall footing. For our wall we went with 4″ of baserock plus the 4″ AB Lite stone for the footing. That means we had to dig a trench ~8″ below grade for the wall footing.

We built a small section of test wall to make sure things were working out as we expected. In the picture on the right you see the section of test wall. This helped us visual what the completed project would look like and also confirmed the height was what we wanted.

Once this was confirmed we used stakes and string to set a line that represented the face of the wall. Down at the far end of the wall I used a garden hose to layout my curve. I then sprayed along the line with landscape marking paint to outline where we needed to dig. Then the trenching commenced!


Most of the DIY articles just say: dig a trench. Well, to dig the trench requires doing a few key things:

  1. Dig the trench in a straight line
  2. Dig the trench the proper depth
  3. (Possibly) dig the trench through hard soil

The first was easy. As I said during layout I used landscaping string to layout the line for the face of the wall and outlined it with marking paint.


My son using the depth gauge to check depth. Looks good!

The second wasn’t as easy. The ground isn’t perfectly level, so how far down do you dig? What is your reference point? To solve this I made a depth gauge out of a piece of PVC pipe and an old 2×4. I set a line along the fence that represented the top of the wall (using string and a bubble level — I marked the fence posts where the top of the wall would lie).


Trenching complete! Test wall in foreground.

We then temporarily screwed a 1×2 on the fence with the top of the board aligned with this line. The depth gauge rested on the 1×2 with the PVC pipe set to be the height of the wall plus the 8″ we needed for the wall foundation. When the depth gauge was level, the trench was the correct depth. Hopefully the picture above helps to clarify this.

To help dig through the hard soil we used the power of water. I bought a soaker hose and snaked this back and forth along each section to dig and we let it run for a couple of hours. We repeated this as needed, and it was a huge help. After soaking we used a lawn edging spade (red handled tool in photo in Tools section) to create a clean line along the face of the trench and then a digging bar and pick axe to break up the soil. Then a square nosed shovel to dig out the dirt. Periodically we’d check the depth with the depth gauge. We continued this until we had our trench! The photo on the right shows the finished trench along with our test wall in the foreground. You can just see the curve at the far end of the wall.



Grading stakes


Laying baserock. Tamping tool in foreground.

Next step was to building the footing, or foundation, for the wall. Your requirements will vary depending on the product you are using and the height of the wall. See the recommendations from your manufacturer. For our 20″ wall we put down 4″ of base rock, and then a course of 4″ blocks. This is a critical part of the project. You want that baserock and first course of block to be nice and level.

To help with this I hammered in some grading stakes, the tops of which were 4″ above the ground. I used a long level to make sure I was level from stake to stake. Then we filled with base rock in multiple passes, compacting in between with a hand tamper. When we got to the top of the grading stakes we pulled out the stakes, filled the holes and checked for low and high spots using a long level.


Laying first course. That kneeler was indispensable, and the deck would get torn out the following summer.

After the base rock went down it was time to lay the first course of block. This is a critical step as that first course determines how well the wall will turn out. So it needs to be straight and level! I laid a string line to line up the backs of the blocks, then used the level and sand to make sure the blocks were level. You can see this in the picture to the right. And a rubber mallet helped to get things seated or to nudge a block one way or the other.  And of course it is always nice to have a Cavalier Spaniel helping out.


Tucker the cavalier helping to move blocks

The Wall


Standard Allan Block two course pattern.

Once the foundation is down the fun part starts. Building the wall! For this phase you just stack the blocks according to the pattern you chose from your manufacture. In the case of our blocks we had to fill the voids in the blocks with gravel. So we’d stack some blocks, then fill. As you stack the blocks check for rocking. Even if you got your foundation course nice and level, there are imperfections in the blocks themselves. Use sand to fill low spots and help keep the blocks from wobbling.

The curved section of the wall was a little more difficult. The problem is as the wall goes up it offsets back a bit, which changes the radius of the wall which means things start not to fit as well. This meant a lot of fiddle and some trimming with a saw. I don’t have a photo of it, but I rigged up some PVC pipe and the garden hose to provide a trickle of water that allowed me to use my circular saw as a wet saw (with a masonary blade). In hindsight I just should have rented a brick saw. So if you are doing a curve you will be cutting block (especially the top caps) so rent a brick saw!

Pace Yourself

One thing to keep in mind when doing a large project is to pace yourself. This took us multiple weekends over a summer. The work is physically demanding, and when you get tired is when you start getting sloppy and make mistakes. We would start early in the morning, then knock off by mid afternoon — and took plenty of breaks.

But it was worth it! We saved thousands of dollars and have tremendous satisfaction that we did the job ourselves.

The Final Product

Here’s a shot of the final product a year later. You’ll notice we tore out the deck and laid a patio (the topic for a future blog post). It was a lot of hard work, but it came out great!



4 thoughts on “Backyard Landscaping: Garden Retaining Wall

  1. Your project is exactly what we are looking to do in our backyard. May I ask what paver/stone you used for the patio and the type of plants that you have running up the fence in the new raised beds?

    -Joe (#2)


    • Hey Joe! The pavers are Quarry Stone Versailles by Calstone in Sequoia Sandstone. The plants are Podocarpus. I think gracillior. I’ve been warned the podocarpus can grow big if you don’t stay on top of them, so I’ve been pruning them pretty regularly. I will have a post on installing the patio real-soon-now.


  2. Pingback: Backyard Landscaping: Paver Patio | Joe's Happy Hour

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