Raised garden beds allow you to create multiple levels in even the flattest yards, while making plants more accessible, improving drainage, and warming soil earlier in the year. Natural stone raised beds easily blend in with stone walkways and other features so the bed doesn't look obviously man-made. Rather than spend money on expensive, quarried stone, you can save up the garden stones you find as you cultivate soil for garden beds. Stones with flat sides work best for stacking, but the stones don't need to be perfectly square.
Lay garden hoses or rope on the ground to mimic the design for the raised garden. These materials work well for creating curves in the design.
Measure the thickness of about 12 stones of various sizes. Add up the total thickness of the 12 stones, and divide this figure by 12 to find the average thickness of the stones. Use this figure to determine the depth needed for the trench. It helps to sort the stones according to size or shape so you can easily find the best stone as you build up the raised bed.
Dig out a trench about 12 inches wide, following the hose or rope outline. Dig the trench to a depth of 5 inches plus half the average thickness of the stones. For example, if each stone is roughly 6 inches thick, dig the trench 8 inches deep. Use a sharp spade to cut the straight edges of the trench. Set the soil aside to use for backfill.
Fill the trench with about 4 inches of 3/4-minus gravel; add the gravel 2 inches at a time and use a hand tamper to pack it tight between layers. Lay one of the stones on top of the gravel periodically and place a carpenter level on top to make sure it's level. Add or remove gravel from the trench as needed to make a level base.
Spread a 1-inch layer of coarse masonry sand over the gravel base layer. Make sure it's level, and adjust the sand as needed.
Lay landscaping fabric inside the trench with about 3 feet of excess fabric overhanging inside the garden bed so that you can cover the inside of the stone wall as you lay the stones. As a general rule, stone walls and raised beds more than 3 feet tall should be left to professional installation, so 3 feet is the maximum amount of excess fabric needed.
Lay the base course of stones on top of the sand base layer. Place the stones side-by-side in the trench. Check every few stones to make sure they're level; add or remove sand as needed to compensate for the varying thicknesses among the stones. Tap the top of the stones with a rubber mallet to set them into the sand base layer when they are level.
Pull up the overhanging landscaping fabric after placing the first layer of stones, and backfill the trench with the native soil on both sides of the stones. Pack the soil tight against the landscaping fabric and front sides of the stones.
Lay additional layers of stone on top of the base course until you achieve the desired height. Stagger the joints on each course to create a stable wall; set each course of stone about 1/2 inch in from the previous course so the soil doesn't push the wall and make it fall. Space the stones as close together as possible. Choose and place each stone carefully to ensure it balances well on the previous course; unlike cut stones of roughly the same size and shape, garden stones vary in size and shape and must be fit together like puzzle pieces.
Lift the overhanging landscaping fabric after laying each course of stone, and add soil to fill in the garden bed. Gravel, stones and other debris also work well as backfill. Stop adding backfill when only 14 inches remains to the desired planter height.
Add a mixture of equal parts clean garden soil and compost to fill the raised bed. Add a 12-inch layer, leaving a 2-inch space up to the top of the planter. Even the largest perennial shrubs rarely need more than 12 inches of garden soil, so using more than 12 inches is a waste. Shallow-rooted plants such as flowering annuals thrive in only 6 inches of soil. Plant your choice of annuals, perennials, edible plants or ornamental plants in the planter.