Durable Raised Garden Beds

Most gardeners are familiar with Mel Bartholomew’s Square Foot Gardening system. It’s one of the most popular gardening systems in the world. He’s sold over 1 million books (more than any other gardening book). With this method you can grow fives times more plants in a given space with less maintenance. You’ll use less water, fewer seeds, and have healthier plants and fewer insect problems. He says it takes half the labor of typical gardening. You don’t even have to dig down in the soil, because the beds are raised above ground. This means you can grow plants almost anywhere, including areas where the soil is really bad. Instead of trying to fertilize and amend lousy soil over a period of years, you use perfect soil right from the start. Be sure to check out his Square Foot Gardening website for full details. In short, it’s a fantastic system and works great.

But there is one drawback that could be improved. Mr. Bartholomew recommends wood for building the raised beds. He probably does this to keep things as simple as possible. Anyone can go to a building supply center, buy some boards and nail or screw them together. But most wood doesn’t hold up well outside, especially when it’s in direct contact with moist soil. In many cases the wood will rot in a few years and you’ll have to rebuild the beds.

That’s the basis of this Instructable– choose more durable materials for building the raised beds so you don’t have to keep rebuilding your garden. Use what is affordable and locally available. For some, it may be easiest to build with interlocking concrete landscape blocks. These come in many different colors and decorative designs. In our area we have very inexpensive compressed earth blocks (CEBs for short), so that’s what we use. CEBs are made with a mixture of soil and about 10% cement that’s compressed in a machine. We use CEBs that are about 5”x10”x4”high. The directions shown here for CEBS are the same for concrete blocks. Just be sure to buy blocks that interlock like Legos.

Materials: sand, crushed gravel, 6 mil black plastic sheeting, CEBs or interlocking concrete blocks, fine mesh fishing net or filter fabric used for French drains

Tools: shovel, rake, level, tape measure, square (2’ framing square is best, but a small one will work), straight 2x4, knife or scissors

The following instructions assume you have cleared and leveled the site, removed the topsoil and positioned your blocks nearby. Choose a sunny site suitable for gardening and a safe distance away from trees. You don’t want trees roots seeking out your garden beds.

Step 1: Weed Barrier

One of the key advantages of this gardening system is the virtual elimination of weeding. This was the main reason we built our CEB garden beds. We have invasive wild grass that makes gardening nearly impossible. Pulling the pesty grass is a non-stop chore. You can’t stop it because the roots are deep in the ground; it just keeps coming back. And when you pull the grass out it often damages the garden plants.

The solution is surprisingly simple and effective. Level a 1” layer of sand where you want the garden bed. The sand reduces the risk of weed stems puncturing the plastic, which is laid in the next step. Lay a piece of 6 mil black polyethylene (‘black poly’ plastic sheeting) on the ground. Cut the plastic sheeting slightly larger than the garden bed to help make sure nasty roots don’t find a way in. Spread some sand or gravel around the edges to hold in place. Then cover the plastic with another layer of sand and about 2” of crushed gravel. The sand and gravel allow excess water to drain away. Without it, water could build up in the garden bed like a bathtub.

Step 2: Level the Gravel and Set the First Course of Blocks

The next step is to level the gravel as accurately as possible so the blocks line up evenly. This will be much easier to do if you use crushed gravel in Step 1 to cover the black plastic. Level the gravel in both directions -- width and length. It helps to have a long, straight 2x4 to use in conjunction with the level. Don’t rush this step or the blocks will not fit neatly together.

Also note, you can make raised beds any size you want as long as they are even increments of your blocks. But a 3’ interior width is a good size that keeps plants within easy reach.

Now you can start setting the first course of blocks. Start in a corner and use the square to make a 90 degree corner between blocks. Set the blocks tight against each other. Use the 2x4 to keep the blocks in a straight line. Work your way around keeping the blocks straight and level and hopefully the last block will fit perfectly. If it doesn’t, then the sides aren’t square and you’ll have to adjust the blocks slightly until they line up.

Step 3: Stack the Second Course of Blocks and Add Mesh

Once the first course is straight, square and level then the rest is easy. You can stack the second course in only two minutes or so. Stagger the blocks so the second course overlaps the first course in a running bond. This locks the courses together.

The next step is to add fine mesh fishing net or filter fabric. This allows water to drain away, but keeps unwanted roots out. Push it tight into all the corners, allowing the excess to protrude out from the blocks in each direction. It helps to use extra blocks set inside the bed temporarily to make sure the mesh or fabric is pushed tight into the corners.

Step 4: Stack the Third Course of Blocks and Trim the Mesh

Trim the fishing net or fabric with scissors as you stack the third course of blocks. Trim the mesh about ½” from the outer edge so it doesn’t show, but yet leave enough so the blocks on top will hold it securely. Again, check and recheck that the mesh is tight in all corners. Otherwise, the weight of the soil will tug on the mesh and destabilize the wall.

Step 5: Add Special Soil Mix and Plant the Garden

Now you can add your special Mel Bartholomew soil mix (or something comparable) at this point. The recipe is free on his website. Don’t use regular soil or you’ll end up with the same problems you started with. Invest in top quality soil and you’ll have the best garden ever.

You can also add stakes through the blocks for vertical gardening and for fencing the sides to keep pets and other animals out. We use ½” steel rebar stakes painted with exterior enamel paint and 1” mesh fishing net on the sides. Use fine mesh on the sides if you have insect problems. You can even add mesh over the top if you want partial shading in hot climates and keep birds out.

So the bottom line is this: invest some time (about two hours for this bed), labor and money in good materials and you’ll reap bumper harvests for years to come.
Pic Final garden 1 and 2

Photo credit: Changamol Kamchuang