Colorado has a range of climate zones that are suited for a variety of different shrubs. Colorado's climate zones range from USDA hardiness zone 3 in the mountains to USDA climate zone 6 on the western plains. Most of the state, however, falls in USDA climate zone 5. Growing conditions vary greatly, depending on the part of the state.
Zones 3 and 4
Zone 3 and 4 are Colorado's coldest zones. These two zones are primarily in the mountains and in the extreme northern parts of the state near the mountains. Winter temperatures in these zones can range from -20 to -45 degrees F. Unlike the lower portions of the state, the mountains get more rain. As warm, moisture-laden air rises into the mountains, it cools and releases its moisture in the form of rain or snow. However, some shrubs and bushes may still require irrigation, depending on the variety.
Most of the eastern plains and parts of the western plains are in zone 5. Winter temperatures in zone 5 range from -10 to -20 degrees F. Because zone 5 areas are warmer, many zone 5 areas don't get a lot of rainfall. The air retains its moisture as it moves over these areas and releases the moisture as the air rises over the mountains and cools. As the air crosses the mountains to the other side, it is drier because its moisture has already fallen over the mountains. As a result, you may need to water or irrigate some types of shrubs on the Colorado plains.
Colorado's zone 6 areas are in the western part of the state. The climate and growing conditions in the western part of Colorado are quite variable. Different areas get more rain than others. However, in western Colorado, most of the precipitation falls in the winter with very dry summers. As such, you will likely need to water or irrigate your shrubs and bushes to keep them healthy. Climate and growing conditions in extreme western Colorado are similar to those in Utah.