Water Wise Landscaping
by Richard Thompson
Wednesday, August 08, 2012
In response to drought and limited water resources a number of new landscaping ideas have evolved to reduce water and maintenance requirements while still providing aesthetically-pleasing landscapes. Collectively, landscaping concepts that reduce water requirements can be called xeriscape, a word coined from the Greek xeros, meaning dry and the word landscape. Xeriscaping was originally conceived in the southwestern U.S., although it was inspired by the gardening traditions of Spain, North Africa and the Mid-East.
One component of water-conserving landscapes is the concept of natural landscaping. Natural landscaping involves plant selection based on local climate as well as site characteristics of exposure, light intensity, soil pH, soil aeration, soil mineral analysis, site drainage, and irrigation water quality. Proper plant selection based on site characteristics improve a plant’s likelihood of survival and resistance pests and disease.
Native species are often preferred for natural landscapes but plant selection should take into consideration the microclimate and topography of the site. In some cases, native plants will not be the most appropriate choice. Man-made installation create desert climates (like parking lots), swamps (like detention ponds, waterways) and artificially-shaded areas. So, effective xeriscaping should match plants with the microclimatic features of the developed landscape site.
For example, plants adapted to wet soils should be used in low spots, waterways, retention ponds, spillways, and areas with poor drainage; drought tolerant plants should be used in dry spots, windy areas, exposed areas, plantings on berms, and plantings in areas against unshaded south or west walls of buildings.
Since natural landscaping is a change in U.S. landscaping philosophy, it can meet resistance from those with preconceived notions of what a landscape should look like. One way to satisfy these notions is to use the ``oasis'' approach to landscape design. Oasis designing involves placing high water requiring, high maintenance, and showy plants in the areas with the most visual impact like the main entry. In less visible areas, xeriscaping can be used.
Aside from these landscaping philosophies, landscape design for water conservation can include grouping plants in the landscape according to their water requirements. By grouping plants with similar water needs, the irrigation system can be zoned so that each group receives only the amount of water required to maintain the plants. This technique has the additional advantage that plants on the same irrigation set will not be under or over watered at the expense of other plants.
An additional way to reduce maintenance and water use is to increase the use of mulches. A three- to four-inch layer of mulch should be used in planting beds to reduce evaporation from the soil surface, moderate soil temperatures, and suppress weeds. Mulches can sometimes replace turf or groundcovers in areas where they require extensive watering or do not cover an area completely. In these situations, mulches provide the additional benefits of requiring less maintenance and not consuming water.
Two more aspects of design that reduce irrigation needs are the use of drought tolerant plants and windbreaks. Drought tolerant plants inherently require less water because they are adapted to arid areas or to regions with frequent drought or with soils of low water holding capacity.
If using turf in the landscape, consider using one of the more drought tolerant species. Grasses with excellent drought tolerance include: bahia grass, Bermuda grass, and zoysia grass. A good drought tolerant plant is centipede grass while St. Augustine grass has a fair rating. Carpetgrass has a very poor drought tolerance rating (Augustine and Peacock, 1985). Another alternative with bahia grass is to allow turf to go dormant during dry periods; bahia grass will turn green again when rains resume.
Windbreaks can be formed by walls, fences, shrub beds, or hedges. Windbreaks reduce wind velocity and can greatly reduce water loss that occurs by evaporation during irrigation and by evapo-transpiration from plants. Properly constructed, windbreaks can reduce wind velocity by 75% to 85% and should be strongly considered for areas that experience steady winds or frequent gusty winds. Effectiveness of windbreaks is determined by height, density, and shape, with height having the greatest influence. The area protected by the windbreak extends downwind the distance of five times the height of the windbreak. For optimum effectiveness, the windbreak should be continuous (unbroken by gaps) “stair-step” in shape, at least head-high, moderately dense (not impenetrable), and evergreen.
Water requirements of landscapes can be reduced by using the design principles of natural landscaping or oasis landscaping. Other methods of conserving water in the landscape include grouping plants in the landscape according to water requirements, increasing the use of mulches, selecting drought tolerant plants, and using windbreaks.
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