Word-Wise About Water-Wise
By: Marita Tewes Tyrolt
Many people use several “low-water-use” plant terms interchangeably, such as drought tolerant, water-wise, xeric, and native. While the meanings of these terms may overlap, there are some very significant differences. Understanding these differences is important for designing and maintaining successful low-water-use landscapes.
Drought Tolerant refers to the ability of an established plant to tolerate periods of drought. The key is that they ‘tolerate’ drought, sometimes by losing foliage and going dormant. These plants require the return of normal moisture levels to resume growth and meet their usual performance expectations. Drought tolerance is only be attained once the plant is established, meaning newly planted drought tolerant plants require supplemental water during a drought.
How much drought a particular plant will tolerate depends on a number of factors: Where did the plant evolve or come from? What is the typical season and duration of drought there? What are the typical temperatures and exposures? What type of soils do these plants typically grow in? And finally, how does that factor into their drought tolerance in your yard?
Water-wise refers to plants that evolved in regions with lower precipitation, thus requiring less water throughout the growing season than most residential landscape plants. But what does that mean? It typically means the length between irrigation or rain is an extended period of time. Some mistakenly think that water-wise means you never have to water them. However, water-wise plants as a category have a wide range of water requirements. Some plants may require water twice a week during the growing season, while others may require water once a week, or only once a month. Still others require no supplemental water—all only after establishment! Interestingly, some water-wise plants may not be tolerant of drought, and may require more supplemental water than usual during a drought.
Xeric refers to the extremely dry end of the water-wise spectrum. These are plants that, once established, do not require supplemental water. In fact, some suffer if they receive supplemental water, such as Pinyon Pine (Pinus edulis) and Mormon Tea (Ephedra).
Native means that a plant originates or is indigenous to a specific area. That area can be variously defined, e.g., it can be a particular canyon, county, state, or a broad geographical region, such as the Southwest. So in selecting native plants for your landscape you should consider the elevation, soils, and water typically available in the plants’ natural habitat or micro-niche. Aspen (Populus tremuloides) in Utah, for example, are native only in the mountain community, typically growing on north-facing slopes where temperatures are cooler and the slower snow melt results in more consistently moist conditions. Aspens often perform poorly in the heat of our valley landscapes.
Several different soil types enhance Utah’s unique landscape. Some of our native plants, including some that are threatened or endangered, are endemic to particular soil types. This means they will only grow where certain geologic formations or soils are found. These soils may have unique mineral content, textural drainage, or microbiological characteristics that native plant species have adapted to, some of which may affect how well the plant stays hydrated.
Plant diversity in Utah ranges from high-elevation sub-alpine mountain meadows to desert badlands. So, it’s important to realize that not all natives are water-wise. While Utah has many water-wise and even xeric plants, we also have many native plants that are mesic, meaning they require consistent moisture, and sometimes a lot of it, such as Alder (Alnus), Willow (Salix), and Mountain Hollyhock (Iliamna rivularis).
Xeriscape is a term that lately seems misunderstood, and poorly designed landscapes leave us with the wrong concept. Barren landscapes—mainly rock and gravel with a few scattered cactus or other plants is not what is meant by Xeriscape. The term Xeriscape was defined and trademarked by the Denver Water Board in 1981. It means that your design incorporates low-water-use plants somewhere in the landscape, and that you group plants together that have similar water requirements (hydrozoning). You can still have a lawn and you can still include plants that require more water, but everything is designed, planted and irrigated within hydrozones.
Six of these principals are good gardening practices no matter what type of landscape you’re planning. Incorporating low-water-use plants, and irrigating by hydrozone, is something that all of us living in a desert can and should do! Converting even one bed to low-water-use or reducing lawn areas can make a big difference in water consumption.
The plants in the remaining hydrozones may not be as familiar to everyone, but will show that a well-designed landscape can be densely planted, beautiful and use less water.
With completion expected in the summer of 2016, we are excited that Red Butte Garden’s Water Conservation Garden is becoming a reality. We hope you will enjoy watching it grow and mature, and the beauty it will provide.