A raised-bed garden built with concrete blocks offers many benefits. The blocks and raised soil level warm quickly in the spring, allowing for earlier planting. Good drainage in a raised bed promotes healthy plants with deep, strong roots. The holes in the concrete blocks make ideal mini-planters for flowers, herbs or strawberries. Building raised beds with concrete blocks requires no special tools and keeps cost low; many commercial raised beds require assembly and have a high price tag.
Choose the location for your raised bed gardens. The ideal site needs a minimum of six hours of direct sunlight every day. Decide how large you want to build the beds. A typical width for a raised bed is 4 feet. This allows you to reach the center of the bed for weeding, planting and harvesting. Length depends on the space you have available and your preferences.
Figure how many concrete blocks you need. Concrete blocks are usually 16 inches long by 8 inches wide. Multiply the amount of feet for the bed length by 12. This gives you the inches. Do the same for the width. For example, a 4-foot square bed is 48 inches long and wide.
Divide the amount of inches of the length, and then the width, by 16. This tells you how many blocks you need for each side. The example bed would need three blocks for each side. Add one block for each width side of the bed to accommodate an 8-inch overlap. You need 14 concrete blocks for a 4-foot square raised bed.
Acquire the blocks. Hardware stores sell them. Sometimes you can find discounted or free blocks in classified ads.
Place the blocks near your chosen site. Line four of the blocks for the width side end-to-end with the holes facing up. Start a length side by placing a block at a right angle to an end block and the outside edge level with the end. Place the rest of the side blocks end-to-end with the first. At the end of the length side, place a block at a right angle, overlapping so the end is level with the outside edge of the block. Finish the square by repeating the pattern.
Spread a thick layer of newspaper (six or more sheets) over the ground inside the raised bed and spray it with water. This acts as a weed barrier. Fill the bed and the holes in the concrete blocks with approximately 16 cubic feet of pre-made soil medium. You can also make your own using one part peat, one part vermiculite and one part compost.