Putting together raised garden beds out of concrete blocks is a great way to make your yard or garden grow in the way you want. Concrete blocks are durable, affordable and easy to work with. In this step-by-step guide, I’ll show you how to use standard 8x8x16″ concrete blocks to build your own raised bed.
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 little maintenance or repairs. Their solid construction can stand up to all types of weather and won’t rot, warp, or break down in other ways like wood can.
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Cost-effectiveness: Concrete blocks are less expensive than brick, stone, or wood when used to build a raised bed. Most of the time, standard blocks cost between $1 and $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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Controlling Pests and Weeds: The solid concrete sides keep animals that dig tunnels, like gophers, out of 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, pick a spot for your garden bed that gets enough daytime sunlight for the plants you want to grow. 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.
- Figure out the Size: A normal cinder block is 8 inches by 8 inches by 16 inches. Let’s find out how much a 4×8 garden needs. Long: 8 feet 12 inches, which is 96 inches, divided by 16 = 6 cinder blocks for one side of the bed, divided by 2 = 12 cinder blocks for the long edges of the garden. Width: 4 feet, which is 48 inches, divided by 16 = 3 cinder blocks, divided by 2 = 6 cinder blocks for the short edges of the garden. Garden Bed Perimeter: 12 x 6 = 18 cinder blocks. Change the math to get the cinder block garden bed size you want.
- Mark Off the Area: To mark off the edges of your bed, use wooden stakes. Then, tie a piece of string or thin rope to the stakes to make a fence around the bed.
- Prepare the Ground: Look at the ground where you are and decide how to get it ready for the bed. If you need to, cut down the grass or dig some holes to make the soil flat for planting. For better weed control, put down a layer of landscaping fabric before putting down your cinder blocks and then filling in the gaps with soil.
- Set up the cinder blocks: Place the blocks around the outside with the holes facing up. The edge of the soil and mulch you’ll be adding will be this, so make sure the cinder blocks are level and not tilted or with gaps between them.
- Adding Another Layer of Blocks (Optional): If you want a bed with higher edges, you can stack your cinder blocks, but you’ll need to double the number you calculated. Even though the cinder blocks are big, you’ll need to make sure they stay in place. Put a wooden stake or a piece of rebar through the first layer of cinder blocks’ holes. Then, put the second layer on top of the first, making sure the stake is still going through the blocks’ holes. Filling them in with dirt secures them further. When you choose the height of your bed, think about what kinds of flowers and plants you want to grow. A shorter border will make small plants stand out more, while taller plants will be able to easily grow up and over the border. For some plants, roots may need more space to grow.
- Fill Around With Dirt: Put dirt around the edges of the cinder blocks (i.e. e. , the openings in the blocks) with dirt and/or mulch. You can also fill the holes in the cinder blocks with soil to keep them in place. This also makes room for more plants if you want to garden in them.
- Fill with topsoil and plant. Put topsoil in the middle of the bed. There you have it! You can now plant any flowers, plants, herbs, or vegetables you want and enjoy your new garden.
What to Grow in a Cinder Block Garden Bed
If you give your cinder block garden the right amount of sun, you can grow almost anything you want.
Still, you should think about how your garden will look as a whole, including how tall your plants will get. 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. Pick plants that grow higher than the border if you want to be able to see them from far away.
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
- Should you use new cinder blocks from the home improvement store or used ones from old buildings? Yes, you should use new cinder blocks from the home improvement store or used ones from old buildings. The fly ash in those old blocks is poisonous and could seep into the ground. This is bad for flowers but really bad if you want to grow food.
- If you want to build a raised bed for the least amount of money, cinder blocks or heavier concrete blocks are the best choice. Each block costs only $2 to $3. How much you spend will depend on how big your garden is and what kinds of flowers and plants you want to grow.
Make a Cinder Block Raised Bed
FAQ
Are concrete blocks safe for raised garden beds?
Whether you plant flowers, shrubs, or food, it’s safe to put concrete blocks around raised garden beds.
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?
Put dirt into the planter blocks. Don’t put potting soil into the bottom blocks until the whole row is laid out.
What is the best concrete block for raised beds?
Interlocking Concrete Blocks are a strong candidate for being the best concrete block to use on a raised garden bed.