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.