While wood does make for a nice aesthetic for your raised garden bed, it will rot over time. Cinder blocks, on the other hand, provide a much sturdier perimeter that will stand up to the elements and provide excellent drainage for growing plants.
Cinder blocks are often confused for concrete blocks, but there is a difference despite their similar appearances. Whereas concrete blocks are made from pure concrete, cinder blocks are made from concrete and a cinder aggregate that makes them lighter. This feature makes it much easier for you to build a raised garden with them.
The quick-and-dirty way of building a raised cinder block garden is to arrange the blocks, fill in the perimeter with dirt, and start planting. But there’s a little more to it if you want it to thrive and look beautiful, too. Here, we’ll walk you through how to create a four-by-eight-foot cinder block garden bed.
Raised garden beds made from concrete blocks are a great way to create customized growing spaces in your yard or garden. Concrete blocks are durable, affordable and easy to work with. In this detailed guide, I’ll walk you through each step of building your own raised bed using standard 8x8x16″ concrete blocks.
Benefits of Using Concrete Blocks
There are many advantages to using concrete blocks for raised garden beds
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Durability – Concrete blocks can last for decades with minimal upkeep or repairs needed The solid concrete construction can withstand all kinds of weather and won’t rot, warp or otherwise deteriorate like wood can.
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Affordability – Concrete blocks are an economical choice compared to other raised bed building materials like brick, stone or wood. Standard blocks can often be purchased for $1-2 each at home improvement stores
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Customizable – Concrete blocks allow you to build raised beds in just about any shape or size you want. Rectangular, square, curved – anything is possible!
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Pest and Weed Control – The solid concrete sides prevent tunneling creatures like gophers from invading your garden. Weeds also have a harder time taking root.
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Improved Drainage – Elevated gardens promote drainage and air circulation around plant roots. This leads to healthier plants.
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Space Saving – Growing upward in a raised bed makes the most of vertical space, great for small yards.
What You’ll Need
Materials:
- Concrete blocks – Calculate how many you need based on dimensions of your planned bed
- Construction adhesive or mortar (optional)
- Landscape fabric (optional)
- Gravel or crushed rock for base
- Nutrient rich soil for filling the bed
- Plants! Seeds or seedlings for veggies, herbs, flowers etc
Tools:
- Tape measure
- Shovel
- Trowel
- Level
- Wheelbarrow
- Safety gear – gloves, goggles, mask
Step-by-Step Instructions
Follow these steps to build your own raised bed from standard rectangular concrete blocks:
Choose Location and Size
- Decide where you want to place your raised bed – in full sun is ideal for most edible plants.
- Determine the dimensions of the bed based on available space. Common sizes are 3×6 ft, 3×12 ft, 4×4 ft, 4×8 ft. Make sure to allow room to walk around all sides.
- For large beds over 3 ft wide, you may need supporting pillars every 4-5 feet along the length.
Prepare the Ground
- Mark the outline with stakes and string where you want your raised bed.
- Remove any grass/plants/debris inside the marked area using a shovel.
- Level the soil using a rake. Compact with hand tamper.
- Add 2-4 inches of gravel over area and rake smooth for drainage.
Lay Out the Base Layer
- Place the first block in a corner – use your level to ensure it’s perfectly upright and flat.
- Add the second block next to it, snugly fitting the ends together. Level and adjust as needed.
- Continue placing blocks lengthwise in a row. Check level and stability as you go.
- Stagger vertical seams between rows. Place blocks in opposite directions.
Adhere Blocks (Optional)
- For sturdiness, apply concrete adhesive or mortar between layers.
- Lift blocks and apply adhesive to vertical end(s). Replace block.
- Adhesive isn’t strictly necessary but it helps fortify the structure.
Build Up Layers
- Check that first layer is perfectly level before moving on.
- Stack the second layer directly on top in the same pattern.
- Repeat for third and any additional layers, alternating block direction for strength.
- Most raised beds need only two or three block layers for ideal height.
Add Decorative Caps
For a finished look, concrete cap blocks can be added:
- Secure flat side down on top layer with adhesive to create a lip around bed.
- Cut blocks as needed to fit using chisel and hammer.
- Caps hide the block edges for a streamlined, polished look.
Fill Bed with Soil
- Add at least 12 inches of rich, fertile soil suitable for growing plants.
- Mix compost, aged manure, peat moss and other amendments to create ideal raised bed soil.
- Mound soil above edge retaining walls to allow for settling.
Caring for Your Concrete Block Raised Bed
A properly constructed raised bed from concrete blocks requires minimal ongoing maintenance but here are some tips:
- Annually, inspect blocks for signs of deterioration or cracking. Remove/replace damaged blocks as needed.
- Replenish soil nutrients each season with 2-3 inches of aged compost or manure worked into the bed.
- Hand pull any weeds that sneak through cracks as soon as you see them. This prevents deep roots from taking hold.
- Concrete raised beds have excellent drainage but avoid overwatering which can waterlog plants.
- In cold winter regions, mulch over soil or cover bed with fabric at end of season for protection.
Inspiring Design Ideas
The rectangular modular nature of concrete blocks makes them perfect for all kinds of creative garden designs:
- Make a beautiful geometric pattern by alternating block direction and leaving gaps between.
- Combine different height blocks for staggered, terraced levels.
- Build a concrete block retaining wall first, then backfill with soil to create an instant raised bed.
- Use concrete adhesive to mortar irregular flat rocks to tops of blocks for a naturalistic look.
- Paint blocks in bright colors for a fun, lively landscape accent.
Building your own raised bed from concrete blocks is a relatively easy DIY project for any gardening skill level. With minimal investment, you can create the perfect customized growing space to plant flowers, herbs, veggies and more!
How to Build a DIY Cinder Block Garden Bed
First choose a patch of ground for your garden bed that gets enough sunlight during the day for what you’re hoping to plant. You’ll also want to be close enough to a water source, or at least within the length of your garden hose so that you can keep your new garden hydrated.
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Calculate the Dimensions
A typical cinder block is 8 x 8 x 16 inches. Lets figure out how much a 4 x 8 garden needs. Length: 8 x 12 = 96 inches 96 / 16 = 6 cinder blocks for one side of the bed 6 x 2 = 12 cinder blocks for the long edges of the garden Width: 4 feet = 48 inches 48 / 16 = 3 cinder blocks 3 x 2 = 6 cinder blocks for the short edges of the garden Garden Bed Perimeter: 12 + 6 = 18 cinder blocks Modify the math to meet your own desired cinder block garden bed size.
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Mark Off the Area
Use wooden stakes to mark off the edges of your bed, then tie a length of string or thin rope to the Stakes to mark off the perimeter of the bed.
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Prepare the Ground
Assess the ground in your area to determine how to prepare it for the bed. Remove grass or do some digging to flatten out the existing soil for planting, as needed. Put down a layer of landscaping fabric before laying your cinder blocks and filling in with soil for improved weed control.
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Arrange the Cinder Blocks
Place the cinder blocks on the perimeter with the openings facing up. This will serve as the border of whatever soil and mulch you’ll be filling it with, so you don’t want cinder blocks to be tilted, uneven, or have gaps between them.
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Add Another Layer of Blocks (Optional)
Depending on the aesthetic you prefer, you may stack your cinder blocks for a bed with higher edges (in which case you’ll need to double the number you calculated). While the cinder blocks are hefty, you’ll still want to secure them on top of each other. Place a wooden stake or a piece of rebar through the holes of the first layer of cinder blocks, then place the second layer over them so the stake is threaded through the openings of the cinder blocks. Filling them in with dirt secures them further.
Tip
Consider what types of plants and flowers you plan to grow when you decide the height of your bed. Small plants will be more visible with a shorter border, whereas taller plants will grow up and over the border easily. Some plants may require more room for their roots to grow.
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Fill Perimeter With Dirt
Fill the perimeter of the cinder blocks (i.e., the openings in the blocks) with dirt and/or mulch. To keep the cinder blocks firmly in place, you can fill the holes with soil as well—that also creates spots for additional plantings should you choose to garden in them.
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Fill With Topsoil and Plant
Fill in the center of the bed with topsoil. Now that youve done the work, you can plant any flowers, plants, herbs, and vegetables you desire and enjoy your new garden.
What to Grow in a Cinder Block Garden Bed
You can grow just about anything you want to in a cinder block garden, provided you’ve got the right amount of sun exposure.
That said, you will want to consider the overall aesthetic of your garden, including how tall your plants will grow. Keep in mind that a typical cinderblock is 8 x 8 x 16 inches, so you’ll have an 8-inch high border with a one-layer perimeter, less any topsoil you add to the interior. Assuming you want to see your plants from a distance, you’ll want to choose plants that grow higher than the border.
Here are some choices for quick and easy plantings right inside those cinder block openings:
- Marigolds (good for keeping out insects and other garden pests)
- Herbs
- Strawberries
- Lettuce
- Beans
Any hardy plant that will thrive in a tight space can be planted in the openings of a cinder block. You could simply fill the holes with topsoil and plant, or you might even consider fitting small potted plants in the holes instead for easy swapping/repotting later. FAQ
- Are cinder blocks safe to use for garden beds? Yes, cinder blocks are safe to use for garden beds, assuming you are purchasing new ones from the home improvement store and not using reclaimed ones from old buildings. The fly ash in those old blocks is toxic and could leach into the soil, which is bad enough for flowers but very bad if you’re planning an edible garden.
- What is the cheapest way to build a raised bed? At just $2 to $3 per block, the most affordable way to build a raised garden bed is with cinder blocks or heavier concrete blocks. Your budget will vary depending on how large your garden is and the type of plants and flowers you want to grow.
Make a Cinder Block Raised Bed
FAQ
Are concrete blocks safe for raised garden beds?
Concrete blocks are perfectly safe to use around raised garden beds whether you plant an edible garden, shrubs or flowers.
How many concrete blocks to make a raised garden bed?
20 blocks will give an interior bed area of 4′ x 8′. Leave a side open to bring in the soil until the new bed is filled. No mortar or special installation is necessary unless you desire a bed which is higher than 8″ raised over the surrounding area. Just set them on the ground!
What do you put on the bottom of a cinder block planter?
Fill the planter blocks with dirt – Wait to fill the blocks on the bottom with potting soil until you’re done laying the entire row.
What is the best concrete block for raised beds?
What is the best concrete block to use for a raised garden bed? Interlocking Concrete Blocks are a strong contender for being the best concrete block to use on a raised garden bed.