Perennials In Water-Wise Landscapes
This NebGuide discusses choosing, establishing and maintaining perennial flowers in water-wise landscapes.
Kim W. Todd, Extension Horticulture Specialist
Dale T. Lindgren, Extension Horticulture Specialist
Dale T. Lindgren, Extension Horticulture Specialist
Drought-tolerant perennials are plants that persist for three or more years with little or no supplemental watering. There are both native and introduced herbaceous plants that are drought-tolerant. Using these plants in Nebraska landscapes will help conserve water, reduce the maintenance associated with watering, and still provide multi-season color and interest. Many drought-tolerant plants perform poorly in areas and seasons of high humidity and rainfall, or with excessive irrigation. For example, some drought-tolerant perennials may perform well in western Nebraska but prove to be less than satisfactory in eastern Nebraska.
Site Selection and Design
Many drought-tolerant perennials do best in full sun and well-drained soil, although a limited number thrive in dry shade. Areas of the landscape that are difficult to water, or are subject to reflected heat and light, are often good locations for drought-tolerant perennials. A primary principle of landscape design to manage water is to group plants that have similar water requirements. Good design also takes into consideration the cultural requirements of each plant, microclimate, the background or setting for the landscape, and the scale or size of the space. Those major factors influence the choice and spacing of individual plants, and how they can best be combined for a beautiful landscape. Size, Spacing and Form-The size of your planting space will influence the choice of plants. Make sure perennials are spaced for their mature size-it is easy to put them too close together when you purchase them as small plants. Some perennials grow larger than the size listed on the label, especially when grown in ideal conditions. Good spacing allows air circulation, which is essential to allow the foliage of drought-tolerant plants to dry adequately and reduce the possibility of disease. The form of many perennials changes as the season progresses. Plants with bold, contrasting forms can be used as individual focal points, while others are best planted in groupings or drifts of three or more. This deliberate use of contrast and similarity will create both variety and continuity in your landscape. Texture and Color-The color, timing, and duration of the flowers is an important consideration, but foliage color also contributes to the overall design. Many drought-tolerant perennials have silver or gray foliage, which shines in low light and acts as a foil for brighter colors. Warm colors attract attention, and make spaces seem smaller and hotter. Cool colors and pastels are tranquil. Unique leaf structure helps many drought-tolerant perennials reduce water loss through transpiration and adds textural interest. Fine, lacy foliage with reduced leaf surface; thick, waxy succulent foliage; or broad, fuzzy leaf blades can reduce water loss from plants and provide many options for using the texture of perennials to extend the visual interest of the landscape well beyond the bloom period. Foliage and seed heads of many drought-tolerant perennials can be left in place well into the winter with a backdrop of ornamental grasses or evergreens, providing an extended season of interest. Leaving the foliage in place until spring holds leaves and snow as insulation, protecting the roots of plants from winter injury. However, care should be taken to keep this material from sitting on the crowns of plants, because good air circulation and drainage are essential to survive through winter.Site Preparation for Establishment
A well-drained, friable (loose) soil is essential for the survival of drought-tolerant plants. This structure will allow the roots of water-conserving plants to extend deeply into the soil. Most drought-tolerant plants in the home landscape benefit from the addition of organic matter to the soil. Organic matter loosens the soil and adds nutrients. Sandy soils, which drain very quickly, benefit from the addition of organic matter by improved nutrient- and water-holding capacity, and reduced runoff of nitrogen and pollutants. If the soil is very poorly drained, small rocks, pebbles, or coarse sand may be added to improve conditions for the most drought-tolerant plants. Loosen existing soil to a depth of at least 12 inches to break up any sites severely compacted by construction or traffic. Thoroughly mix organic matter such as coarse compost, shredded leaves, or a combination of these materials, into the loosened soil at a ratio of approximately one part organic matter to four parts soil. For example, use 3 inches of organic matter on a soil loosened to a depth of 12 inches.Maintenance
Even the most drought-tolerant perennials require supplemental water until they are established, as well as during periods of extended drought. The smaller the root system, the more frequently you will need to water newly installed perennials. Check the soil beyond the root zone as well, and apply one-half inch to 1 inch of water weekly inclusive of rainfall. Gradually reduce the amount of supplemental water, but continue to monitor the condition of the plants. Mulch new and established perennials with a layer of material 1 to 2 inches deep to retain soil moisture, suppress weed growth, and reduce erosion. Organic mulches are recommended for all but the most drought-tolerant plants. Medium-textured wood chips, shredded bark, chopped leaves or a combination of these materials look natural and improve the soil composition as they decompose. Inorganic mulches like rock or gravel hold heat and reflect light, and may damage the plants they are intended to protect. Fertilize drought-tolerant perennials only when the plants show signs of diminished vigor or chlorosis. The breakdown of organic mulches adds nutrients to the soil, but fertilizer may eventually be needed if mulches or compost are not regularly replenished. Most drought-tolerant plants will perform well for years without division and may actually be destroyed if they are disturbed. Others will respond to overcrowding by dying out in the center, becoming spindly or failing to produce vigorous blooms. Drought-tolerant perennials may be divided and replanted as soon as the soil is workable in the spring or in late August to early September. Gently lift the old clump, and remove dead pieces with a sharp knife or spade. Split the plant into two or more sections, and place each section in a new planting hole at the same depth or slightly higher than the original plant. Backfill with soil that is consistent with the surrounding area, and water until the soil is saturated.Do not tamp the soil or otherwise compact it. Following is a list of perennials that have demonstrated a tolerance of Nebraska moisture conditions, including soil moisture stress, when planted in well-drained soils. The list includes native and non-native or adapted plants that are not invasive. The most drought-tolerant plants are indicated with an asterisk. Bloom times are approximate, since they are influenced by climate factors and microclimate. Exposure refers to the amount of sun that each plant prefers; many plants will tolerate more or less than an ideal exposure, but habit and bloom may be affected. Only a few of the many cultivars that may be available are listed in the following table.
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Index: Horticulture
Ornamentals
Revised August 2003