A hedge is a collection of shrubs usually planted in a row or group that forms a barrier or boundary. Some plants used as hedges are actually small trees--for example, Canadian hemlock, Leyland cypress or arborvitae, and can get very large if not pruned. Prune a hedge so the bottom is slightly wider than the top so the sun shines on the lower branches. This prevents the hedge from becoming woody at the bottom. Most plants that are suitable for fast-growing hedges can be pruned back drastically without affecting the overall health of the plant.
Take a soil test to find out the type of soil you have and its pH level. Choose a hedge that is suitable for your native soil--a hedge is a permanent landscape planting and adding amendments every year can be expensive and time-consuming. Assistance with a soil test can be obtained by contacting your local county agricultural extension office, which will give you the information needed to take an accurate soil test. Also notice if the area where you expect to plant the hedge is soggy or well-drained. Not all shrubs used as hedges can survive long periods with roots sitting in wet soil.
Find out the planting zone you live in by looking at a USDA horticultural zone map. It will give you an idea of the minimum temperature that is common during winter in the area where you plan on planting the hedge; choose a shrub accordingly. Notice that nearly every description of a shrub that you will see when shopping includes the appropriate planting zone in the description.
Measure the area where you plan on placing the hedge--the eventual size is important in that process. You do not want to overwhelm your landscape with a fast growing large hedge such as a Siberian elm, but you want the hedge to be functional according to your needs. Also be sensitive to how the eventual size of the hedge will affect your neighbors. For example, account for how much shade will be cast on your neighbor's landscape once the hedge matures.
Look at a list of shrubs that are popular for fast-growing hedges, either online or at a local bookstore or library, that meet the criteria you have established. You can also ask your local county agricultural extension office for suggestions. Shrub descriptions will tell you the growth rate of the shrub as well as its eventual size.
Ask friends and neighbors for suggestions if they have an attractive or fast-growing hedge on their property.