Selections to handle water extremes—be it scarce, soggy, or both.
As everyone knows, water is one of the main factors in the success or failure of any plant. Too much or too little water given to a young tree or pricey ornamental easily turns into a dead plant and wasted time, effort, and money.
The adage “right plant, right place” bears even more importance in an era of water shortages. “It’s critical. We’re going to have to scrutinize more… we’re going to have to question what we’re growing where,” comments Jennifer Riley-Chetwynd, co-director of the One World One Water (OWOW) Center at MSU Denver and director of marketing and social responsibility at Denver Botanic Gardens, which jointly runs OWOW Center.
Species selection that requires ongoing supplemental irrigation is now a luxury few areas can afford. Simply keeping established, zone appropriate plants alive is challenging in some regions today. And while a return to native plants has been a battle cry for years, water shortages may increasingly inspire the use of appropriate non-natives that thrive in similar global climates to broaden options.
In Colorado, which is a steppe environment, that means looking to Mongolia, South Africa, and Argentina’s Patagonia region, says Riley-Chetwynd. “We’re introducing plants from Argentina… testing them and bringing them to market through Plant Select®.” A nonprofit collaboration of Colorado State University, Denver Botanic Gardens, and professional horticulturists, Plant Select focuses on finding and distributing beautiful landscape plants that will easily thrive in high plains and intermountain regions while using fewer resources. Plants chosen exhibit eight attributes: flourish with less water; thrive in a broad range of conditions; are habitat-friendly; are tough and resilient in challenging climates; are one of a kind/unique; resist disease and insects; have long-lasting beauty; and are non-invasive. (For a full list of Plant Select plants, downloadable design templates, and a list of Horticulture Best Practices for the Western U.S. which includes some great practical tips, look here.)
“Not all of these are natives [to the U.S.],” comments Riley-Chetwynd. “We definitely believe in natives, but things are changing. You can’t just rely on what has worked in the past… yes, it’s going back to basics, but it’s also looking to other similar regions.”
A recent LA Times article on drought-hardy picks for Southern California, for instance, consulted a South African-trained landscaper (among others) and included plant suggestions from the four other Mediterranean-zone climates: the Mediterranean Sea area; the Cape of South Africa; southern Australia; and central Chile. Among the selections were: hummingbird, white, and black sage; pigeon point coyote bush; California buckwheat; scarlet bugler; Channel Islands tree poppy; scented geranium; lion’s tail; emu bush; and rosemary.
Cal Water, the largest regulated American water utility west of the Mississippi River and the third largest in the country, also includes Mediterranean zone plants from beyond California in its list of low-water and drought-resistant plants, trees, vines, ground covers, and turf here. Turfgrass recommendations included: buffalograss; hybrid Bermudagrass; and Victoria zoysiagrass.
SUCCESS IN THE WEST
Recommended Sizes At Install
Perennials: 1 quart
Shrubs: 1 gallon
Trees: Max 1.5” caliper
- Amend existing soil with squeegee at a minimum of 6” depth.
- Provide well-drained, lean soil.
- Rich, organic soil and wood mulch are not ideal.
—Denver Botanic Gardens
In terms of turf, of course, it’s not news to landscapers that many water-wise landscape advocates—and increasingly some government authorities—often call for decreased areas of turfgrass in drought-ridden areas.
“Useless” municipal grass on traffic medians and such are the biggest targets, but many efforts are also aimed at voluntary reduction of residential lawns. While contrary to an LCO’s livelihood, such initiatives could also provide opportunities for those willing to adapt.
“Landscape professionals are going to hear more and more and more on water-wise landscaping,” says Riley-Chetwynd. “There’s nothing like a crisis to make people a little more aware.” As a former employee of Rain Bird, Riley-Chetwynd began to grasp the importance of water conservation when she ran water education and awareness campaigns for the company. “Boy, my eyes were opened…water became my issue. I’m practically an evangelist now,” she says.
Just last month, the legislature in Colorado passed House Bill 22-1151 as a water conservation measure. A state-wide initiative, the Turf Replacement Program will pay property owners to replace their lawns in favor of native plants and landscapes. “I hope people turn to professionals,” says Riley-Chetwynd. “It’s not just about tearing out turf and other living elements and putting in rocks. We need plants. It’s going to open up a lot of opportunity for landscapers.”
Like many, Riley-Chetwynd says she is “not anti-turf, [but] pro smart-use.” She adds, “We deal in scarcity of water, but that’s not everyone’s issue.”
Flood Resistant Plants
Indeed, many areas not in ongoing drought are experiencing the opposite end of the spectrum. Extreme storms dumping record amounts of water in a short period, coastal erosion, rising sea levels, and watershed concerns are making more people aware of excess water and its effects. Rain gardens, once a novel concept, are becoming a norm and even legally required in some areas. The role of plants in proper stormwater management is receiving more attention than ever before. Engineering and landscape design are becoming powerful partners in creating effective drainage that also fights pollution of our waterways.
According to Dr. Bert Cregg, professor in the Departments of Horticulture and Forestry at Michigan State University (and co-author of Turf ’s April article on tree transplant success), when environmental stresses are considered, trees vary more in flood-tolerance than any other trait. He says upland trees such as pine, hickories, and most oaks may be damaged after a week or less of flooding; while trees that are native to floodplains, such as cottonwoods, can withstand months of inundation. As one would expect, bottomland species are best adapted for flooding, especially in late Winter or early Spring.
These trees include (numbers represent zones):
- Red maple (Acer rubrum) 3-9
- Silver maple (Acer saccharinum) 3-9
- River birch (Betula nigra) 4-9
- Hackberry (Celtis occidentalis) 3-9
- Sweetgum (Liquidambar styracifl ua) 6-7
- Tupelo or blackgum (Nyssa sylvatica) 3-9
- Sycamore (Platanus occidentalis) 4-9
- Eastern cottonwood (Populus deltoides) 2-9
- Swamp white oak (Quercus bicolor) 4-8
- Bur oak (Quercus macrocarpa) 3-8
- Black willow (Salix nigra) 2-8
- Bald cypress (Taxodium distichum) 4-10
- Elms (Ulmus spp.) 2-9
DROUGHT TOLERANT SHADE TREES
- Eastern redcedar (Juniperus virginiana) 2-9
- Bur oak (Quercus macrocarpa) 3-8
- Northern red oak (Quercus rubra) 3-8
- Kentucky coffeetree (Gymnocladus dioicus) 3-8
- Hackberry (Celtis occidentalis) 3-9
- Chinkapin oak (Quercus muehlenbergii) 4-7
- Northern catalpa (Catalpa speciosa) 4-8
- London planetree (Platanus x acerifolia) 5-9
- Shumard oak (Quercus shumardii) 5-9
- Live oak (Quercus virginiana) 7-10
—Arbor Day Foundation
Davey Tree offers many of the same recommendations for flood tolerant trees in its blog, with the addition of thornless honey-locust (Gleditsia triacanthos var. inermis), appropriate for zones 3-9. Davey also makes suggestions for flood-tolerant shrubs. These include:
- Winterberry bush (Ilex verticillate) 3-9
- Red-osier dogwood (Cornus sericea) 2-7
- Bayberry (Myrica pensylvanica) 3-7
- Swamp azalea (Rhododendron viscosum) 4-8
- Sweetspire/Virginia willow (Itea virginica) 5-10
Worst of Both Worlds: Wet & Dry
Of course, not all areas are consistently wet, or consistently dry. Many regions experience periods of extreme rain and long, hot, dry weeks. The blog of Green Prism Consulting, a tree care company in Gainesville, GA, says that with more drastic climate extremes, it can be smart to choose plant varieties that fall not just within your plant zone, but extend a bit further to accommodate a wider range of conditions. According to Green Prism, black gum/tupelo trees, as well as swamp white oaks, while listed for their flood tolerance, can also handle at least a moderate drought tolerance. Nuttall oak (Quercus texana), zone 6-8, is also listed in this category.
Ornamentals that make this desirable wet and dry list from Green Prism include:
- Coppertina ninebark (Physocarpus opulifolius ‘Mindia’) 3-8
- Eastern sweetshrub (Calycanthus fl oridus) 4-9
- Possumhaw viburnum (Viburnum nudum) 5-9
- Pink muhly grass (Muhlenbergia capillaris) 7-11
- Blazing star (Liatris spicata) 3-9
- Red switchgrass (Panicum virgatum ‘Shenandoah’ 5-9
Stan Wilson, general manager of Austin, TX-based Environmental Survey Consulting (ESC), says in his blog how Central Texas and the Southwest have experienced both extended drought and historical flooding in the past years, resulting in altered landscape conditions. He says ESC has found a few plants in both their residential landscapes and ecological restoration with “strong future” status in response to unpredictable weather extremes. Some examples below:
- Tropical sage (Salvia coccinea) (9-10; will reseed 6-8)
- Frogfruit (Phyla nodifl ora) 6-11
- Big muhly (Muhlhenbergia lindherimeri) 6-10
- Bushy blustem (Andropogon glomeratus) 5-9
- Horsetail (Equisetum hyemale) 4-9
- Roughleaf dogwood (Cornus drummondii) 4-9
With the many climate zones within the U.S., areas differ in their ability to support different plant species without the need for supplemental water. The Outdoor section of EPA’s Water Sense initiative offers helpful tips on irrigation, landscaping, and has links to native plant lists for every state (some states have multiple entries). You can access the native plants list for your state here.
Menapace is editorial director of Turf. An avid gardener and nature enthusiast, she has worked as a plant nursery professional, a Park System naturalist, and floral designer. She has been a professional writer for over 30 years and escapes from her desk to hike or garden every chance she gets.
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