Reinventing your Landscape classes, Reno, Spring 2017

Incorporating climate change adaptation and mitigation strategies into urban horticulture education

By John Cobourn, Steve Lewis and Heidi Kratsch, University of Nevada Cooperative Extension

Three Extension faculty members from Western Nevada became aware that few homeowners plant shade trees in strategic locations to reduce air conditioning needs for their homes in summer. They met with a local non-profit sustainability group to find out what they thought of the idea of presenting classes on topics like this one. The group, called GreenACTnv, liked the idea and offered to co-sponsor the classes with Cooperative Extension in Spring 2017.

Rather than limiting the topic to climate change and shade trees, the group decided to broaden the class content and to title it: “Reinventing your Landscape: How to make your landscape more livable and resource-efficient while saving you money.” In this context we could ask participants to consider changes that make sense for homes in an arid climate zone where average temperatures are warming. We could suggest they create “Integrated Sustainable Design” for their landscapes. These design ideas involve harvesting and using rain, sun, shade, vegetation, mulch and compost to conserve resources, creating a comfortable environment and saving money.

To bring this concept to life, we decided to use the example of strategic plantings of deciduous shade trees as the class focus. Research-based information is available. For example, we found a journal article titled: “Urban heat islands and use of shade trees and high albedo surfaces,” by H. Akbari, et al., of Livermore Labs, Berkeley. Among other things, the authors found that average urban area temperatures have risen 0.5 to 3 degrees C (0.9 to 5.4 degrees F) since 1940; electricity demand in cities increases 2-4% for each degree rise C (or 1.8 degrees F); and 5-10% of urban energy demand is from heat island effect.

Another journal article: “Potential of tree shade for reducing residential energy use in California,” by Simpson and McPherson, 1996, presented these findings: 1. Optimum reduction in air conditioning costs are gained by maintaining two mature deciduous trees on the west side of a home and one on the east side. 2. This can reduce air conditioning energy use 10 to 50 percent (estimated 45% in the coastal mountains of California). 3. Trees should shade windows in summer if possible. 4. In the northern hemisphere, planting deciduous trees directly south of a house will do little to reduce energy costs in summer and can increase winter heating costs by shading south-facing windows.

 

 

 

Figure 1. Because of seasonal changes in the angles of the sun’s rays, shading the west side of a home is more effective in summer than trying to shade the south side. In summer, the sun’s pathway is so high during mid-day that most south-side trees would not shade the house unless they were very large and dangerously close to the house.

 

 

 

The planning group decided to hold the first class after work on a weekday, free of charge, with email notices to the sustainability group’s membership list and an article in the local newspaper. The first half of the class, which introduced the above information, was taught by Extension Water Specialist, John Cobourn. The second half, explaining the nuts and bolts of how to plant trees, get them established, and maintain them over time, was taught by Extension Horticulture Specialist, Heidi Kratsch.

Tree-dominated landscapes require up to 70 percent less water than turfgrass-dominated landscapes (Rosenberg et al., 2010, Value Landscape Engineering: Identifying costs, water use, labor, and impacts to support landscape choice). So, Kratsch discussed techniques for reducing or eliminating lawn areas, using sheet mulching to kill grass around trees and solarization for removal of larger areas of lawn. She also taught methods for proper tree planting, with an emphasis on performing a pre-plant percolation test to make sure the new tree will have excellent drainage, and on techniques for improving drainage on difficult sites.

Appropriate irrigation for trees after turf removal was an important concept for participants to learn. Trees planted in lawns become dependent on the relatively frequent, shallow turfgrass irrigation. Lawn removal without conversion of the lawn irrigation system to drip irrigation or adjustment of irrigation rates for the trees severely weakens the trees and shortens their lifespans. Irrigation to trees should be deeper and less frequent than irrigation to lawns. When irrigated appropriately and mulched with organic matter, properly sited trees can be a real asset to a climate-resilient home.

The class drew 25 participants, and a lively discussion followed the presentation. Seven participants returned responses to a Survey Monkey evaluation. Respondents stated that they intended to renovate their landscape (86%), that they would plant shade trees on the west side of their homes (86%), and that they would install a water-efficient irrigation system (66%). When asked if they desired more classes on “Reinventing Your Landscape for resource efficiency, decreased maintenance requirements and cost savings,” 71% said Yes, with the most popular topics being pruning shade trees and fruit trees, choosing shade trees and fruit trees for Western Nevada, and native plants that provide color and attract pollinators.