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By Marita Tewes Tyrolt, Red Butte Garden director of Horticulture
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 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 do these factors contribute to 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. 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 supplemental water 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. 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), 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. 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.
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 similar requirements
- Use mulch
- Exercise proper maintenance
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 planned Water Saver Terrace, in Red Butte Garden’s Water Conservation Garden (currently under construction) is designed to demonstrate this concept of xeriscaping, and will have five different water-wise hydrozones.
- Zone 4 – will include plants commonly used in home landscapes, but will only be watered twice a week. Our goal is for visitors to see that plants can still perform beautifully when watered less, motivating them to irrigate their own gardens and landscapes less as a result.
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.
- 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.
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.
In the meantime, for more information about water-wise gardening, you can check the Garden’s program offerings or the following websites:
Reprinted from the Red Butte Garden Fall 2015 Newsletter