Selecting Drought-Resistant Plants
BY JULIE ERSHADI
For many of our clients, water conservation is a prime motivator when they decide they want an eco-green sustainable landscape. It’s one thing to install systems that utilize low-flow irrigation, rainwater harvesting, or graywater reuse. Some people are wondering how we can use less water altogether in our landscapes. The answer lies in plant selection.
One of the easiest ways to find water-wise plant material is to look for drought resistance, but what does that really mean? What makes a plant drought resistant? Consult the experts, and you’ll discover that there are three main adaptations plants have developed for coping with dehydration beyond the climate’s normal seasonal changes.
These are known as avoidance, tolerance, and succulence.
Drought avoidance describes the behavior of annuals. They escape dry conditions by simply not existing—that is, they mature, germinate, and then die, all in a single season. The next season, the seeds they produced sprout into new flowers that do the same. While the ingenuity of this mechanism is intriguing, it’s just not all that helpful to us landscape professionals.
The same goes for drought tolerance, also known as dormancy.
Plants with this adaptation typically shed leaves or turn brown during dry periods. They don’t die, but they might as well, for how scuzzy they look when they dry out. So, toss these out too when it comes to designing a drought-resistant, aesthetically-pleasing landscape.
Succulence is the third category of drought-friendly adaptation.
Succulents store water in thick leaves, stems or roots. All cacti are succulents, and so are non-cactus desert plants such as agave, aloe, elephant trees, and many others. These plants absorb large quantities of water into their shallow root systems in short periods of time, a mechanism developed by their natural desert environment’s light, brief rain showers.
However, even succulents aren’t always the best plant material for a drought resistant landscape. In order to understand why, we must look more closely at what our clients really mean when they say they want a drought-friendly yard. They are looking for a landscape that they don’t have to irrigate heavily, but which will still look amazing. They want plant material that will thrive, not only survive, in the naturally occurring precipitation for the given climate. Even in the South, there are regions with too much rainfall for succulents, which can become waterlogged. In those same regions, more thirsty plants will suffer when the dry season does come.
Where’s the middle ground? How do we create a landscape that will look beautiful with just as much water and sun as its environment will naturally provide with minimal irrigation? Here’s the secret: You don’t need to reinvent the wheel. To create a landscape designed for your climate, pick plants that have been designed by your climate. This means that native plants, and exotic noninvasive plants from similar climates in other parts of the world, are your most powerful friends in this effort.
“Our mantra is ‘right plant, right place,’ ” said Don Rainey, statewide coordinator for the University of Florida’s Green Industry Best Management Practices program. “Here in Florida, we have two dry seasons and a wet season. Generally, plant selection is critical also because of our sandy soil profile, which doesn’t retain much in terms of nutrients or water.”
Florida has three main climate profiles in the northern, central, and southern regions of the state. Each of these areas will be better suited to a different plant selection, with room for overlap. In the northern panhandle, where Rainey says precipitation averages 65 inches per year, flowering plants are good choices.
“We do have a plant selection that, once established, can generally do well without any irrigation,” Rainey said. “If the plant is suitable for its location, it will no longer need extra water unless it’s in severe drought conditions.”
Through thoughtful plant selection, the contractors Rainey works with can design landscapes that look gorgeous without the need for a great deal of irrigation to supplement what they receive from their environment. They have the ability to draw from a wide selection of both Florida-native and exotic noninvasive plants to create lush, vibrant, drought resistant landscapes. The amount of greenery and color possible is a far cry from what you might first think of when you hear that the landscape is drought resistant.
While Rainey is tasked with helping green industry contractors in his state, most state university extension offices will have their own dedicated horticultural experts, as well as an on-line plant databases. The selections in these digital libraries have been researched and refined by the experts, and they can save you a great deal of time. This tool will guide you to a wealth of information on what plant material is best suited for your region.
Mengmeng Gu, the ornamental horticulture specialist with Texas A&M University’s extension program, emphasized the need to pay attention to regional variation when choosing low-watering plants. “In Texas, we have some very nice native plants that would do well under drought conditions but not under wet conditions,” she said. “The Texas mountain laurel does very well in the central and western part of Texas, but not that well in east Texas, where it’s too wet.”
“It also depends on what kind of drought tolerant we’re talking about,” she said. “Are we talking about a totally unaltered desert environment, or just restricted irrigation?” “In landscapes, there are some plants that use less water than others, though not as little water as cactus,” said Gu. “That’s a good thing, too, because most people do not want to use just cactus for their landscape.”
It may be helpful to keep Gu’s words in mind when consulting with your clients over a project. How eco-green are they hoping to be? If some irrigation is an option, you may not need to be as stringent in your drought resistance considerations when choosing plants for the design.
Still not sure you can create a drought-friendly landscape that’s also lush and beautiful? Consider the work of Hunter Ten Broeck, owner of Waterwise Landscapes, Inc., Albuquerque, New Mexico. Ten Broeck has studied his city’s climate in order to know what plants will do well there. As a result, his desert-friendly designs are characterized by vivacious, colorful flowers that thrive in the aridity of New Mexico and similar climates of other regions around the world.
“We live here in a place that gets an average of 9 inches a year and sits at 5,000 feet in elevation, so the circumstances here are very unique,” he said.
“We have to find plants, some native and some not, that have similar climate needs.”
With that combination of low precipitation and high elevation, plants need to be drought resistant and cold hardy. “We pick plants that are native to here,” Ten Broeck said. “We also use a lot of cold hardy Mediterranean plants, including herbs like rosemary, sage, and thyme, as well as different lavenders. We use some South African plants—the cold hardy ones from the mountains there—and plants from the arid parts of Asia.”
Even with a global selection, you may have to opt for plants that do have dormancy stages if you’re trying to be as irrigation-free as possible. Ten Broeck has ways to work around this necessity. “I try to pick plants that, if they have winter dormancy, they have some sort of unique structure, maybe an unusual bark on them or something. That way you can leave an interesting texture through the winter.”
It’s also clever to place drought avoidant plants—ones that go dormant—close to perennials. This way, there’s not a total loss of color during the dry season. “I try to pick things so that there’s color as long as possible throughout the year,” Ten Broeck said. “When I do a design, I’ll have some early spring bloomers, late spring bloomers, early summer bloomers, late summer bloomers, some fall bloomers and then some things with winter interest so it’s not just colorful one time of year and dull the rest of it.”
With these principles in mind, by no means does a drought resistant landscape need to be a boring and glum sight.
On the contrary, picking the right plants for the climate and soil conditions means you can produce a vibrant, creative spectacle of foliage that derives most of its hydration from naturally occurring moisture—not a high-volume irrigation system. Your best bet is to follow Mother Nature’s lead. Find aesthetically pleasing plants that have adapted to live in just the climate where you’re working, and you’ll be on your way.