How to Select a Hedge for the Illinois Climate

Identify the local climate zone and choose from shrubs that will survive the coldest winter temperatures likely to occur at the planting site. These are listed on a scale from 1 to 12 by the U.S. Department of Agriculture, based on the average extreme annual low temperature -- the most basic criteria determining whether a plant will survive. USDA plant hardiness zones in Illinois range from 5a to 7a. The northwestern corner of the state is in USDA zone 5a, with an average extreme minimum winter temperature between 15 and 20 degrees below zero Fahrenheit. Other than the northwestern corner and the Chicago area, the remainder of the northern half of the state is in USDA zone 5b that reaches 10 to 15 degrees below zero F as extreme lows each winter. The southern half of the state is equally divided between USDA zones 6a and 6b, with an extreme low temperature range between zero and 5 degrees below zero F, and 5 and 10 degrees below zero F, respectively. There is a tiny area of zone 7a in the extreme southern tip of the state where the extreme minimum winter temperature is between zero and 5 degrees F. The Chicago metropolitan area is an anomaly in USDA zone 6a, even though it is about 200 miles north of the other areas of the state that fall in USDA zone 6a.

Narrow the choices to those hedge plants that are adapted to high humidity and summer rainfall. This can often be determined by the region where the plant originates. For example, plants from the relatively arid regions west of the Rocky Mountains often fail to thrive in Illinois. However, plants from the eastern United States where the rainfall patterns and humidity levels are similar to those found in Illinois are likely to grow well. The same holds true for species originating in continental climates of Northern Europe and Central Asia. Avoid planting shrubs from the desert and Mediterranean climates of places like southern Europe, northern Africa, south Africa, Chile, Australia and the Middle East -- even if they can survive the winter temperatures of Illinois, they are likely to succumb to disease in the relatively moist conditions of the Illinois climate.

Consider local climatic variation within the state. For example, much of Illinois is part of the prairie ecosystem where high winds are common, and northern Illinois, especially the Chicago area, is subject to heavy snowfall in winter. Evergreen hedges are the best choice in areas where blocking the wind or drifting snow is a concern -- plant on the windward side of the property if this is a concern. Also, dense urban areas like Chicago tend to have greater extremes of heat in summer, especially if the hedge will be planted adjacent to a large paved area. Select shrubs that tolerate heat and drought if local conditions warrant. These shrubs are generally characterized by relatively small leaves, especially those with a waxy coating or gray-green color.

Make the final selection based on the specific conditions of the planting site, functional requirements and personal taste. Sun exposure, soil type and depth to water table can be used to further narrow the selection process. The size of the hedge may be determined by the available space or the desired function. Choosing flower color, leaf texture and growth habit are a matter of personal preference and the way the shrub will fit with the overall design of the landscape.

Measure the length of the area for the hedge. Determine the best spacing for the particular shrub when planted as a hedge. Divide the length of hedge by the number of feet the shrubs will be spaced, add one and purchase this number of plants.