There are many reasons to build a raised bed for your vegetable garden. Inhospitable soil, a gardener’s special needs and digging pets are just a few. Recently my mother decided to build a raised vegetable bed against the back wall of her house, so we spent Mother’s Day doing just that. The bed she designed was 16 feet long by 27 inches long by 16 inches high.
- Cement blocks (24)
- Half blocks (4)
- Cap stones (13)
- Sand (10 – 60 lb. bags)
- Rebar (30 – 24″ bars)
- Concrete adhesive
- Rubber mallet
- Sledge hammer
- Stakes and string
Begin by deciding where you’d like to place your raised bed and how big you’d like it to be. Measure carefully then use those measurements to calculate how many blocks, half-blocks and cap-stones you will need. We used approximately 1 60 lb. bag of sand for every 3 blocks. Rebar should be at least 6″ longer than the height of your wall. The longer it is, the more sturdy it will be. Make sure there are no pipes or drains directly below where your wall will be so you don’t risk damaging them when you install the rebar.
Once you’ve done the math and picked up your supplies, you can get to work. First, clear away all weeds and debris. It also helps to loosen the soil approximately 6 inches below the surface. Once that’s done, level the bed — especially the area where you will be building your walls. The more level you can get it now, the quicker the wall building will go later.
If you are building your bed against a wall or fence, you will need to install some sort of water barrier to protect the structure from rot and/or pests (dirt against exposed wood is a termite’s dream). For easiest installation, use a water barrier with an adhesive on one side. It costs a little more, but the time savings and ease of installation are worth it.
If weeds are a problem in your garden-to-be, cover the bed with weed blocking fabric. Newspaper is another way to suppress weeds, but because it breaks down over time you may want to use something more permanent under the wall itself. If you are growing vegetables with deep root systems, leave the center of the bed free of weed block so the roots can pass freely. This is especially important for root vegetables.
Once the fabric is down, pour a layer of sand on top of it. This will make it easier to level the blocks as you install them. Install one block at a time working from one corner to another, leveling as you go. Tapping the blocks with a rubber mallet can help. For best results, tie a string between two stakes as a guide to keep the wall straight.
Fill holes in cement blocks with sand to help stabilize them. Insert rebar (rebar should be at least 6 inches longer than the height of your wall) into the outside corners of each hole along the side closest to where the dirt will be. This will help support the weight of the dirt and make sure the wall does get pushed outward over time.
Hammer rebar down into the blocks using a sledge or other heavy hammer. Note that the rebar may stop when it hits the weed cloth, but another hit or two should push it through. If that doesn’t work, you may have hit a rock. Reposition the rebar and try again. For maximum strength, make sure you always place the rebar along the side of the block that will be supporting the dirt.
Once the wall is complete, and the blocks are filled, wet the sand thoroughly. This will help the sand settle down into the blocks and stabilize the wall. When it dries, add cement cap-stones to the top the wall using a cement adhesive to keep them in place. Once the wall is complete, cement blocks can be painted or brushed with white-wash for a more professional (or more colorful) look.
Once your walls are finished, just add soil and plant. The number of blocks and quantity of other materials you’ll need will depend on the size and height of your bed and the materials you choose. Be sure to do the math ahead of time to avoid installation problems and multiple trips to the store.