Written by: Penelope Hyland, Colorado Master Gardener
As I drive around the city of Pueblo and Pueblo West, I am amazed at how many new and older homes are landscaped with just rock. The common belief is that even though landscaping with rock is more expensive initially, in the long run it pays off with zero maintenance. While that statement is not entirely correct, there are also other things to consider before deciding to landscape with rock or not.
The first issue to address is that of zero maintenance. The idea is that you will entirely limit the growth of weeds. Whether landscape fabric is laid underneath the rock or not, weeds will still grow. This is Southern Colorado, and the winds blow a great deal of the time bringing in dust, dirt, and seed. Birds and other animals also drop seed and the result is weeds growing above the rock. Weeds will also grow beneath the landscape fabric (which is why we typically don’t recommend using landscape fabric). It is difficult to weed in a rock landscape and so most people resort to using a chemical spray which needs to be applied regularly and then also goes into the environment. This is also costly and time-consuming. So putting in a rock landscape to eliminate the need to deal with weeds is not effective.
A second consideration of using rock or not concerns care of our ecosystems. We now know that many ecosystems around the world are in a state of decay along with billions of insects and pollinators that are crucial to our existence in producing edible foods.
The third consideration to take into account is the matter of how the use of rock landscape increases the local heat index by several degrees. Southern Colorado is a semi-arid region that sees high temperatures with low precipitation in normal conditions. Rock absorbs, retains, and then reflects heat back into the atmosphere raising the temperatures around that area. This in turn, combined with asphalt and concrete use, creates a heat island.
Urban heat islands can change the local climate, increasing temperatures 6-8 degrees above surrounding areas by reducing evaporative cooling effects of vegetation and contributing to unstable weather patterns and climate change. This leads to an increase in energy consumption to cool homes, buildings, and vehicles which also leads to an increase in air pollution.
Rock landscaping provides no nutritional value to the ecosystem and raises the temperature of the soil which increases plant respiration rates and throws off the Ph levels of the soil. Rock landscapes contribute to the stress of nearby plants. In the middle of summer heat, rocks can reach temperatures of 140-170 degrees! These extreme temperatures effect everything in their area including surrounding air temperatures, plants, animals, and humans. Heat is the leading cause of weather-related deaths.
Another side effect of using rock as the primary landscape is an increase in virga (precipitation that evaporates before reaching the ground) instead of actual precipitation. Virga has been increasing in Southern Colorado, especially over the area of Pueblo West. As the heat from the ground and rocks rises in the atmosphere, it turns the falling moisture back into gas form and produces virga. So, in addition to increasing the overall temperature of the urban area, it also reduces the amount of rainfall.
It is possible to use rocks strategically and effectively in landscape. For example, driveways and walkways of a light-colored aggregate reflect heat instead of absorbing it. Rock can be used around the A/C unit or in a dry creek. If possible, use rock on the north and east sides of a home and avoid using on the south and west sides which have greater sun exposure.
Rock gardens are also an option using drought resistant and native plants along with crevice gardens which utilize plants tucked into rocks. Remember that the heat from the rocks will increase their respiration rates.
One or two large rocks can be used as a focal point very effectively and surrounded by native plants, shrubs, and/or trees.
Awnings and shade sails especially over A/C units help to reduce consumption.
The presence of vegetation can lower nearby air temperatures by as much as 4 degrees. So in planning a landscape design, see where vegetation can be included around rocks if rock has to be included in the landscape.
Other options include planting trees which provide a lot of shade and don’t need much maintenance. The area around the planted tree can be expanded to include a larger circle or other geometric feature that can be mulched to help protect the tree and increase the amount of organic matter. Other shrubs and vines can also increase shade and provide vegetative matter to reduce overall temperatures.
A variety of other low-maintenance and weed-suppressing ground covers can also be used for landscaping. Short prairie grasses are also an option instead of turf grass or rock as are all types of native perennials that will produce many different colors of blooming flowers all summer.
In an area where extreme summer temperatures are an issue, it makes sense to do what we can to help reduce those temperatures and their effects. Sometimes we wonder what we as individuals can actually do to make a difference. In the case of reducing heat index and maintaining the health of local ecosystems, there is something that every individual can do in their own landscape – plant more trees and more native vegetation. A single plant makes a huge difference.