Word Wise About Waterwise
Submitted: Jan. 10, 2019, 1:51 p.m.
Many people use several “low-water-use” plant terms interchangeably in horticulture, such as drought tolerant, waterwise, xeric, and native. While the meanings of these terms may overlap, there are some very significant differences. Understanding the differences between these terms is important for designing and maintaining successful low-water-use landscapes.
Drought tolerance 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 to normal moisture levels in order to resume growth and meet their usual performance expectations. In addition, drought tolerance is only attained once the plant is established, meaning newly planted drought tolerant plants require supplemental water during a drought in their first couple of years.
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 in its native habitat? What type of soils do these plants typically grow in? And finally, how does this information relate to the conditions in your yard?
Waterwise refers to plants that evolved in regions with lower annual precipitation. These plants naturally require water less often throughout the growing season than most typical residential landscape plants. It is a common misconception that water-wise means you never have to provide supplemental water for the plant. Rather, the term water-wise encompasses a broad range of water requirements, depending on the plant species and the habitat where it is native. Some plants may require water once a week during the growing season, others only once every other week or once a month, still others require no supplemental water. Even plants that require water two or three times a week still fall within the range of water-wise. Interestingly, some water-wise plants may not be tolerant of drought, and may require supplemental water during a drought. And just as with other landscape plants, waterwise plants require supplemental water until they become established.
Xeric refers to the driest end of the water-wise spectrum. Xeric plants require supplemental water until establishment, but afterwards do not. In fact, some suffer if they receive supplemental water, such as Pinyon Pine (Pinus edulis) and Mormon Tea (Ephedra spp.).
Native refers to plants that originate from or are indigenous to a specific area. This area can be variously defined, e.g., a particular canyon, county, state, or a broad geographical region, such as the Southwest. In Utah, plant habitats, and thus plant diversity, range from high-elevation, sub-alpine, mountain meadows, to desert badlands, so it’s important to realize that not all native plants are xeric or even waterwise. Utah is also home to many mesic, or water-loving, plants. Some moisture loving native plants include Alder (Alnus spp.), Willow (Salix spp.), Red-osier Dogwood (Cornus sericea), Mountain Hollyhock (Iliamna rivularis) and Shooting Star (Dodecatheon dentatum). Aspen (Populus tremuloides), which perform poorly in the heat of our valley landscapes, are native only to the mountain community, where they typically grow on north-facing slopes, where temperatures are cooler and the slower snow melt results in more consistently moist conditions.
Utah’s unique landscape includes several different soil types. 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. When designing and selecting native plants for your landscape, consider what type of native habitat you are going for, including the elevation, soils, and water typically available in that habitat. And take advantage of micro-climates, as it’s always fun to explore what might be perfect for that different or challenging spot.
Xeriscape is a term that is also misunderstood, and poorly designed landscapes leave us with the wrong concept. Barren landscapes—mainly rock or gravel with a few scattered plants is not what is meant by Xeriscape. The term Xeriscape was defined and trademarked by the Denver Water Board in 1981, and refers to designs that incorporate low-water-use plants, and group plants together that have similar water requirements (hydrozoning). Xeriscapes can still have a lawn and plantings that require more water, but the landscape is designed, planted and irrigated within hydrozones.
The seven principles of Xeriscape gardening are summarized as follows:
- Create a plan or design (according to site conditions, exposures and use)
- Make appropriate soil improvements
- Incorporate low-water-use plants
- Incorporate small turf areas appropriately
- Irrigate effectively, by grouping plants with similar water requirements
- Use mulch
- Exercise proper maintenance
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 be doing. Converting even one bed to low-water-use or reducing lawn areas can make a big difference in water consumption.
The Water Saver Terrace, in Red Butte Garden’s Water Conservation Garden is designed to demonstrate this concept of Xeriscaping, and has five different water-wise hydrozones:
- Zone 4 – includes plants that are commonly used in home landscapes, but will only be watered two to three times per week. Our goal is for guests to see that even these commonly used plants can still perform beautifully when watered less.
Plants in these remaining hydrozones may not be as familiar, but show that well-designed landscapes can be densely planted, beautiful and use less water.
- Zone 3 – watered once a week
- Zone 2 – watered every other week
- Zone 1 – watered once a month
- Zone 0 (Xeric) – After establishment these beds will not receive supplemental water other than during periods of extreme drought.
For more information about waterwise gardening, you can check the Garden’s classes and workshops or the following websites: