How to Create an Awesome Raised Garden Bed

How to Create an Awesome Raised Garden Bed

Photo of conrete garden beds

Are you looking for an easier way to garden? Many people, including myself, have difficulties working in gardens down at ground level.  Even raised garden beds that are 6-8” high are too low for many of us to work in comfortably.

I wanted to be able to continue gardening, despite my disabilities, so my sister and I designed these tall raised beds made from concrete blocks.  These awesome beds are not only easy to work in, but they have also proven to be incredibly productive.

If you know of anyone that could use this type of raised bed to help them
be able to garden, please share the link to this article with them!

Sitting on the side of a concrete raised bed

By adding solid “cap” blocks on the top, these beds provide a comfortable surface to sit on.

 

Kneeling to work in a raised garden bed

If you are able to kneel, the soil is nearly waist high while you work.

Although it costs more to create these concrete raised beds, they are pretty permanent.  We plan to use ours for over 20 years, so our pro-rated cost per bed over time (for both soil and blocks) is under $18 per year.  These beds have also been extremely productive.  The value of the organic food we've harvested from them has paid back the full cost of construction in under 3 years.

You Can Get Incredibly High Yields

The added benefit of these tall beds is that it provides nearly 18” of topsoil for your plants. This added depth can drastically increase the yields from your small garden. It’s been mind-blowing how much food we’ve been able to harvest from one of our 50-square-foot beds!

Large organic harvests from raised garden beds

Because we usually grow 2 or 3 crops per year in each bed, our total harvests are often even higher! Mind you, it's also important to build up a fertile and biologically-rich soil in order to achieve such high yields.

There are a couple of disadvantages:

  1. You tend to lean and twist your back when working in these beds.  I make a point of frequently changing the side I'm working with – lean to the right for a while, then turn around and lean to the left. If you are able to kneel, then this won't be a problem for you. (see the photo below)
  2. These concrete blocks can get very hot in the summer sun. I can't sit on them while wearing shorts in hot weather. In addition, all the concrete may cause a mini “urban heat effect” in gardens – an advantage in cool climates, but a disadvantage in areas with scorching hot summers.

By following the step-by-step directions below, you too can create these wonderful garden beds!

1) Choose the Size of Your Concrete Garden Beds

How large are the beds that we use? Each one is roughly 4 feet wide by 16 feet long, and about 18 inches high. We've found this to be a very comfortable size to work with.

Dimensions of raised concrete garden bed

This is our favorite size for our concrete raised beds.

You can create different size garden beds, but each side will need to be in multiples of the 16” length of the blocks, plus the width of one block. The smaller the beds, the more expensive it will be per square foot of garden space.

I have found my current width to be very comfortable to work with.  While it’s possible to add another block (16”) to the width, you would then have to stretch over 2 feet to reach the middle of the bed. That’s not comfortable for most people.

In order to save money on concrete blocks and to maximize the space in your garden, I wouldn’t recommend designing these beds less than 8 feet long (6 blocks).

It’s possible to create much longer beds than what I have, but then it becomes a bit of a pain to walk all the way around the beds to reach the other side.  I’ve really enjoyed working with the length of my current beds.

It's a good idea, whenever possible, to create paths at least 3 feet wide between the beds. Our plants often grow so large and vigorously, that they spill out of the beds and start blocking the paths. Our 2-foot-wide paths sometimes get too crowded for us to be able to walk down them without risking damaging the plants.

A crowded path that is too narrow

I would recommend a minimum of 3 feet wide pathways around these beds, if at all possible. Our pathways are a little over 2 feet wide, and they often get crowded from vigorous plants overflowing from the beds.

You can also choose how high to make the beds – a single level or double level, with or without solid cap blocks. The perimeters of the short beds are about 10 inches high (with cap blocks), with the raised soil inside being 6 inches deep.  The perimeters of the taller vegetable beds are about 18 inches high (with cap blocks), with the raised soil inside being about 14 inches deep. You may also have additional topsoil in your yard underneath these beds, which would add additional depth to the soil.

 

2)  Building These Garden Beds

Choosing the Garden Site

Besides choosing a site close to your home, with a healthy amount of sunlight, it's also important to choose a site that doesn't have any sudden changes in slope.

The ground doesn’t have to be perfectly level for these beds – though that would be nice! The blocks can handle gradual changes in slope. But if the ground suddenly changes direction, the blocks won’t sit evenly on each other, and they will rock and shift around.

A gentle slope is best

Avoid installing concrete block beds where there is a sudden change in slope.

These beds can run downhill on gentle slopes, if necessary, but if your slope is moderate, you'll want to run the long beds across the slope and use them to create mini terraces.

Setting the Blocks in Place

To help stabilize the base of the block walls, we sunk the blocks an inch or two into the soil (by removing the sod directly underneath the blocks). You can choose to create short beds or tall beds, depending on how many layers of blocks you choose to use.

Sink blocks into ground

We sink the blocks a couple of inches down into the soil.

Always alternate the blocks when you stack them on top of each other. Don’t put one block directly on top of the one below.

Don't stack blocks directly above each other

Alternate the blocks when you stack them on top of each other.

None of these blocks are mortared together. Unless you create a deep well-drained footer below the blocks that goes below the frost level, cold winter weather could frost-heave the blocks and crack any mortar. It’s better to just stack them together.

How many blocks do you need in order to create the same size beds that I use?

Short beds:

  • (30) 8″x8″x16″ concrete blocks (hollow type)
  • (30) 4″x8″x16″ cap blocks (solid type)

Tall beds:

  • (60) 8″x8″x16″ hollow concrete blocks, stacked two deep
  • (30) 4″x8″x16″ solid cap blocks

Lining the Inside of the Bed

I lined the inside of the blocks with a heavy-duty weed barrier, to keep the soil from sifting out between the cracks (which I’ve experienced with a retaining wall). I don’t put the barrier on the bottom of the bed, under the soil, because I want my plant roots to grow as deeply as possible. I secured the top of the fabric underneath the solid cap blocks.

Construction of concrete block garden bed

To prevent soil from sifting out between the blocks, line the inside of the blocks with heavy-duty weed barrier fabric. I don't put this fabric on the bottom, underneath the soil, as I want my plant roots to grow as deep as possible.

 

It's important to purchase the highest quality fabric available, as you want this material to last as long as possible. How much do you need? For short beds, about 40 square feet.  For tall beds, about 80 square feet.

I’ve found out the hard way that empty blocks can sometimes shift over time from the pressure of the soil inside the raised bed.  I had stabilized the base of the bottom row of blocks, but a few of the blocks in the upper rows have shifted a bit over time.  These would have remained more stable if I had filled the hollows inside the blocks with gravel (soil might sift out between the cracks).

A shifted block in a raised bed

Some of the upper hollow concrete blocks can shift out of place, unless you fill the hollows with something like gravel.

However, most of our blocks have remained in place, so for now, we're not going to go through the time and effort to needed to stabilize them any more. We'll just reposition the shifted ones. If this issue gets any worse, however, then we'll put some effort into a more permanent fix.

Cap Blocks or No Cap Blocks?

I love using solid concrete cap blocks on top, as this gives a great surface to sit on.  If you leave off the cap blocks, you can fill the hollows in the blocks with soil for additional planting space. Just be aware of three possible issues with this:

a)      You will need to stretch more than 2 feet to reach the center of the bed

b)      The soil may sift out from between the blocks (if they are more than one block high)

c)      In hot weather, the soil inside these blocks will heat up and dry out much more quickly than soil inside the bed

3) Adding Soil to These Raised Beds

When choosing the soil to fill these concrete raised beds, I strongly encourage you to consider using topsoil instead of potting soil. These beds are permanent and require a lot of soil to fill them. Potting soil is not only much more expensive, but it decomposes fairly rapidly.  To keep the bed full with potting soil usually requires that you will need to replace the soil that has disappeared every year (often 1/4-1/3 of the depth of the bed).

When I fill these raised beds full of soil, I like to have the final soil depth reach just below the bottom of the cap blocks. This way, the cap blocks provide a little bit of wind protection to small seedlings in the garden bed, and they also help to keep my mulch in place.  In addition, any wet soil is a few inches below where I'm sitting on the edge, so my clothes don't accidentally soak up mud or moisture while I'm working in the garden.

In order to have the soil settle at that height, it's necessary to fill the bed initially all the way to the top of the cap blocks. Loose soil that is at first 20″ deep will often settle 4-5″ lower over the next few months.

So, how much soil do you need to fill the size beds that I use?

For the short beds, about 1.2 cubic yards.  For the tall beds, about 2.75 cubic yards.

 That's It.  You're All Done!
You're Now Ready to Plant Your Garden. 

ENJOY!

If you know of anyone that could use this type of raised bed to help them
be able to garden, please share the link to this article with them.  Thanks!

Raised bed garden

  • Kelly says:

    Thank you so much for your in depth descriptions and photos! I’m moving to a new house and starting all over again with my garden, which is daunting, but it’s exciting to plan from scratch and make this one my best garden ever! I live in an area with frost, and have been having a hard time deciding if I need a foundation, or a gravel base, or mortar. I plan to make it 3 courses tall and use alternating caps so I can sit along the edge. Planning to do dry stack for now and see how it goes. How many years old is your dry stack bed that pushed out?

    • Debra says:

      Hi Kelly! My beds were only 2 years old when that started happening, I think mostly due to heavy freezes in our cold winters. It won’t help to mortar the blocks together unless you also provide a solid foundation that goes below the frost line (which is 2 feet in my climate, so it isn’t practical where I am). Otherwise, the mortar will just crack apart when the soil shifts as it freezes. A 6″ deep well-drained foundation of gravel may help, but I don’t think that will help when the soil in our raised beds freezes hard around the sides and expands sidewise. I would be tempted to either fill the hollows in the blocks with gravel, which will drain well and may help prevent the blocks from shifting sidewise. Or pound 2-foot rebar into the soil inside the hollows in the blocks, at diagonal corners. Wished I had an easy cure! We’re mostly just living with it, and correcting spots that get too bad. Good luck!

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