Select a half whiskey barrel at your local garden center. Choose one with wheels if you intend to move it once it has been planted.
Flip the barrel over and drill four quarter-sized, evenly spaced holes on the bottom to ensure proper drainage.
Decide where you want the barrel to be and move it there. Layer lightweight material such as empty plastic bottles or packing peanuts in the bottom of the planter if you want to reduce the weight and conserve soil. Most ornamental bedding plants only need 10 to 12 inches of good soil to thrive.
Add the potting soil, leaving 2 inches between the top of the soil and the top of the planter. Soil spilling over the edge will be messy and unsightly, so be sure to leave room for the final layer of mulch that you'll be adding after the flowers have been planted.
Select your first plant and plant it in the center of the container. Many gardeners choose to place the largest specimen in the middle and surround it with plants of decreasing size until the ones near the edge of the barrel are vines spilling over the sides and onto the ground below. Other gardeners who prefer a more symmetrical look use plants of roughly the same size and shape.
Settle the plants gently into the soil using your fingers and the hand spade. After they have all been planted, water them in and cover the exposed soil with an inch or two of mulch.