Brick planter boxes can last longer in your garden area than boxes built from wood or synthetic materials. If you build brick boxes that are more than 60 cm (2 feet) high, you will need to alternately layer each row of bricks by staggering the brick mortar joints. This helps the boxes retain their stability. For boxes that are less than 60 cm high, you can simply layer the bricks on top of one another in straight rows.
Use a tape measure and chalk spray to mark out the desired length and width of your planter box. With a shovel, dig a trench around the border 15 cm (6 inches) deep and 7.5 cm (3 inches) wide around the marked area. Check the alignment of the trench with your level and add or subtract soil where applicable with a spade.
Pour 500 g of mortar powder for each 100 ml of water and mix it thoroughly with a trowel until it becomes a paste. Use the shovel to fill the trench to the top with the mortar. Smooth the mortar flat with the spade. Allow 48 hours for the mortar slabs to dry.
Beginning at a left corner of the dried planter box slab, spread mortar for two to three bricks. With the trowel, spread mortar about 8 mm (1/3 inch) thick onto an end of the first brick to be laid. Press the brick down firmly into the mortar. Align the brick using a level. If necessary, tap it into position with a rubber mallet. Continue this to finish laying the first row of bricks.
Cut a brick in half with a brick cutter to start the second row of the planter box. Use a trowel to spread mortar for two to three bricks onto a left corner of the first row of bricks. Spread mortar about 8 mm (1/3 inch) thick onto an end of the half-brick. Press the half-brick firmly into position. Continue the process along the second row using whole bricks.
Alternate the rest of the rows, using a half-brick to begin every other row, until the brick planter box is at its desired height. Allow the mortar to dry for 48 hours before putting plants in the brick box.
Test the mortar's consistency by putting some onto your trowel and turning it upside-down. The mortar should stick if it is at the right consistency. Also, be sure to clean your tools before the mortar dries.