Fill in around the root balls with soil, making sure that the tops of the roots are just barely below the soil surface. Planting too deeply may cause your plants to rot. Add a slow-release fertilizer such as Osmocote, and mix it into the soil surface. Mount the planter securely in the desired location, and water well. There are a variety of window boxes to choose from.
Redwoods are attractive, but they tend to dry out quickly.
Terra cotta window boxes keep the soil from drying out and hold salt and chemical deposits away from the soil. Plastic window boxes have the advantage of being the lightest to carry and install.