Building a brick garden wall is an attractive way to contain the soil for a planting bed. The first order of business is to decide the scope of your project. Walls over 3 feet high usually require some kind of permit. A brick retaining wall that is only used to enclose a garden, provided it is not too high, does not require any permission. A reinforced brick wall is typically over 3 feet and also requires rebar supports. Since you are not going that high with your brick wall, internal supports are not necessary. Decide how many bricks you want to stack and the thickness of the wall. Determine how many sides it will have. It could be between 1 and 4 sided depending on the landscape around it. Lastly, decide how strong you’d like it. It is conceivable to simply stack bricks in a pattern, but using mortar is the best way to ensure the wall is strong.
If there is already a foundation on top of which the brick wall will be built, then you have one piece already in place. Otherwise you will have to dig a shallow trench, level the bottom and construct a temporary frame for a poured concrete foundation. Make the trench about 4 inches wider than the foundation will end up being. It need not be more than 3½ inches deep, so 2x4s will work for the frame. Depending on the number of sides the wall will have, the foundation frame will parallel it. For instance, a 4-sided foundation frame will consist of one outer box and an inner box. The distance between the boxes represents the width of the foundation and should be even. Make sure the frame is level and held in position by stakes before you pour the concrete. Smooth out the concrete and keep it moist for a few days so it can cure. Once cured, you can proceed with the wall.
Laying Out the Wall
Snap a chalk line along every side of the foundation representing the outer edge of the wall. This will be a guide for laying the brick. Cut up several dozen pieces of 3/8-inch dowel to use as spacers and set the first layer of bricks in place along the foundation guided by the chalk line. Set the spacers between each brick. Mark the placement of the first row of bricks on the foundation with a pencil.
Mortaring the First Row
Mix up the brick mortar, making sure it is thick enough to hold its shape when you make an indent with the trowel. Apply an even coat on the bottom of each brick, smoothing it out as you do. Set the bricks one at a time on the foundation with the chalk line and the pencil marks as your guides. Once the entire first row is in place, fill in the 3/8-inch gaps with mortar, packing it in tightly. Check the level of the first row and make sure everything is even.
Double Thick Wall and Subsequent Rows
Depending on the size of the planter, you may choose to make the wall doubly thick. Mark the position of the inner row of bricks by spacing them with the dowels and noting their position with a pencil. Set the bricks in the same manner as the outer layer. Check the level periodically as you move along the wall. As you make the second row, make sure to stagger the placement of the bricks. Mortar joints should be in the middle of the brick directly beneath it.
Check your progress frequently, making sure the wall stays level and the spacing between the bricks is uniform. Mortar has to be used within 2 hours of being mixed, so only mix up as much as you can use in that time. Keep the bricks and mortar moist for a day or two so, like the foundation, it cures properly. Now you are ready to fill in the garden area and use it for planting.