Select plants that are rated for the amount of sunlight the sidewalk receives, and that will thrive when heavily crowded. If your sidewalk is on a busy street, consider selecting plants that are known to withstand pollution well, such as cornflowers, black eyed Susan and goldenrod. Tall, narrow plants are most appropriate for small gardens, with shorter flowering plants at their base.
Pry up any brick or concrete in the spot where you want the garden to go. Cover the soil with 3 inches of organic compost and turn it into the soil with a shovel. Loosen the soil at a depth of 8 to 12 inches.
Set the plants in their containers in the garden so you can decide how you want to arrange them. Place the taller plants in the back of the garden, with the shorter flowering plants in front.
Dig planting holes that are large enough to fit the root balls of the plants. Remove the plants from their containers and lower them into the planting holes. Firm the soil around the roots and water until the soil settles.
Cover the soil between the plants with a 1 inch layer of organic mulch. Place decorative garden rocks in any exposed spots that are too small to fit another plant.