Choose a shrub that grows well in or close to your climate. You can overwinter some shrubs indoors if it's too cold in your area, but some will not do well without hot humid summers. You will also want to look for slow-growing, drought-tolerant plants. If they grow too quickly, you will need to prune constantly. Not being in the ground, the plant will rely on you as the only source of continual water and nutrients, so if they are drought-tolerant and you forget to water them, they will have a better chance of survival.
Read the label on the shrub you have purchased to make sure the container is large enough. If there is no label, choose a container that is 2 to 6 inches larger than the one the shrub is currently in. Fill the bottom 1 to 2 inches, depending on size, with stones. This will ensure the drain holes do not get clogged with soil and water will be able to drain through.
Mix 1 part potting soil with 1 part loam-based compost to fill your container. Certain shrubs will require different types of soil, so refer to the label on the shrub. One example is shrubs in the Ericaceae family, such as rhododendruns and heathers, need a lime free compost.
Place the container in the desired location before filling it with soil if it is very large. Check the type of shrub to see whether it needs full sun, partial shade or full shade before placing the container. If the container is small enough to be moved easily, you can position it later.
Mix a time-release shrub fertilizer into the soil well and fill the container to 1 to 2 inches from the top depending on the size of the container and the size of the root ball you will be planting. This will leave some room for watering inside the container.
Dig a hole slightly larger than the root ball in the center of the soil. Turn the container that currently holds the shrub on its side and carefully remove the shrub. Do not try to just pull the shrub out by the trunk or you could damage the plant or its roots. Place the shrub's root ball in the planting hole and push the soil over it. Hand tamp down firmly.
Water the soil until the water comes out of the bottom drain holes. This will ensure the roots were dampened and will help them to establish in to their new home. Keep the soil moist for the first week and then water when the top of the soil feels dry.
Apply a water-soluble fertilizer after you start to see new growth on the shrub and in summer and fall of each year. Follow manufacturer's directions as to the amount to apply.
Repot each late winter or early spring. Gently remove the shrub, prune off some roots if you want to keep the plant small, and place new soil in the pot. Put the shrub back in and continue to fill in around the roots with new soil. Some shrubs will require repotting once a year, others every two or three years, depending on the quality of soil. If you want the shrub to grow larger, you can repot it in a larger container.
Prune the top to shape or to keep the plant small. If you prune the roots, cut off an equal amount of top growth to keep the water and nutrition needs balanced. Pruning should be done in the late winter or immediately after flowering, if it is a flowering shrub.