Concrete blocks are weather resistant, sturdy, relatively easy to work with and inexpensive, making them ideal for simple landscaping projects. They can be held together with mortar like bricks or laid out like garden edging. They can be both decorative and functional, serving as walls, benches or planters.
Decorative Garden Wall
Concrete blocks come in more designs than what most people picture, namely the heavy block with two holes. While those can be very useful in a garden setting, more attractive blocks, with a lacy appearance, can be used to create beautiful walls to separate a section of the garden or even enclose it with a short wall. Simply stack the blocks, securing them with mortar to whatever height you choose. As with any free-standing wall, be sure to first dig a trench and set the first row of blocks in the ground, building up from there.
Concrete Block Planters
The commonly pictured concrete block makes for an easy garden edge/planter combination. Simply lay out the blocks with the holes facing upwards. Line your garden, your deck, your walkway or other area with as many blocks as you like. Completely edge the garden/deck/etc. or lay out a few blocks for just one side. Fill the holes with potting soil and dirt, then plant flowers to create an edge of continuous blooms. With the blocks, it'll be harder for weeds to creep up and inside. To make certain, however, use plastic liner beneath the blocks first.
Concrete Block Bench
For a more creative use, stack and mortar the concrete blocks to form the legs of a bench. Add a plywood plank across the top and you have a simple garden bench. Be sure to treat the plywood with sealant to slow down the effects of weathering. For a nicer bench top, use wooden planks. Cedar and cypress are weather resistant and require less treatment. You may also use redwood or other hard woods that could be stained or painted.