Water Management in the Garden

Published: July 5, 2012

For the past several summers, an article detailing the need to conserve water when gardening might have been considered unwarranted because of the abundance of rainfall we received. The hot, dry weather this summer is a vivid reminder of the importance of water to the livelihood of plants. Additionally, its shortage reminds us that water is our most precious natural resource and should be conserved.

It has been estimated many gardeners use about twice the amount of water in their landscapes than is necessary. Gardening using techniques that carefully manage water input often is referred to as “water-wise” gardening. The latter not only conserves the supply of this valuable natural resource, it also reduces the amount of money gardeners spend on water.

Water-wise gardening is a step-wise process, the first of which is proper planning. The latter includes the establishment landscape areas or zones according to the amount of supplemental water garden plants need. For example, the “high-use” zone is occupied by plants that are supplied with water whenever they need it. Annual beds and borders as well as patio plantings fit into this zone. Plants selected for is zone are for other virtues they possess and not for drought tolerance. Therefore, plants in this zone might suffer under even slight drought stress.

The “medium-use” zone contains plants that receive water during their establishment and at times of water stress such as during dry periods. Plants used in this zone should have good drought tolerance. Many perennial borders as well as woody ornamentals plantings around the home are typical of this zone.

Plants in the “low-use” zone do not receive additional water except during the period of their establishment. Once these plants are well-rooted, natural rainfall is their only water source, even during periods of drought. As a result, plants selected for this zone must be very drought tolerant. Areas in the landscape distant from the home often fit into this zone.

Shade is important when planning a water-wise garden in that it reduces water consumption by keeping surfaces cooler, thus reducing transpiration and evaporation. Shade especially is useful in places where it keeps surfaces of buildings, etc. from heating which, in turn, keeps plants near them cooler. Shade combined with proper use of mulch is a very effective way to conserve water in the garden.

The second step in water-wise gardening involves plant selection. Selecting plants for the high and medium water use areas is relatively easy. Practically anything that will survive the temperatures typical of a Missouri summer can be used in the high-use zone. Selecting species known for their ability to withstand water stress (e.g. marigold and zinnia) will help to conserve water even in the “consumptive” zone.

Most plants that can adapt to Missouri’s temperatures while forming deep root systems are suitable for planting the medium-use zone. Many perennial plants along with a select few annuals are good candidates for this zone. Additionally, the majority of ornamental woody plants fall into this category.

The selection of plants used in the low-use zone presents quite a challenge in that drought tolerance is of utmost importance. Native species of plants, or imported species of plants native to hot, dry areas, are good candidates for the low-use zone. Please refer to MU Guides G6629, Flowering Annuals: Characteristics and Culture; G6650, Flowering Perennials: Characteristics and Culture; and G6660, Wildflowers in the Home Landscape for additional information that will make plant selection easier.

The third step in water-wise gardening involves soil improvement. Since many landscapes in Missouri have poor, shallow soils, the additional of organic matter is very important to water-wise gardening. Amending soil with organic matter helps to increase its water-holding capacity and the likelihood that plants will survive during droughts. The thorough incorporation of about four inches of well-decomposed organic matter on an annual basis is considered to be a “best management practice” for all types of gardening and in all of the afore-mentioned gardening zones.

Proper plant establishment is necessary if plants are to survive in the medium and low-use garden zones and is the fourth step in water-wise gardening. Even though the goal for these two zones is to encourage plants to be able to survive with little or no additional water, newly planted plants with limited root systems need water to become established. In the case of perennials, adequate water is most important the first year after planting, but may be important during the several years, depending upon species. During hot, dry weather, about one to two inches of water per week should be supplied if not received as rainfall. Slow, thorough soaking of the soil will make optimum use of water resources during the period of plant establishment.

Mulching is the fifth step in water-wise gardening because it helps to conservative water while at the same time acting as a deterrent to “water robbing” weeds. Mulches serve to block evaporation from the soil as well as to reduce soil temperature. While many materials are available for use as mulches, organic mulches usually are preferred. They should be fairly fine in texture and non-matting. Shredded bark, pine needles, sawdust, (dried) grass clippings and straw are examples of organic mulches. Landscape fabric or black plastic can be used below organic mulches to improve weed retardation and aid in evaporation control.

It is well documented that healthy plants are more drought-tolerant than are weak (or damaged plants) plants. Therefore proper plant maintenance is the sixth step in water-wise gardening. Well-fertilized plants will have healthier, deeper root systems capable of absorbing more water. Keep in mind, however, fertilization is not important during periods of drought when plants are not actively growing. Instead, delay fertilizer application until fall or spring when weather conditions are more ideal for plant growth. Pruning excess foliage can help reduce water usage by reducing the surface area carrying on transpiration. However, avoid severe pruning which tends to open the plant to more sunlight and water loss.

The final step in water-wise gardening is to practice proper irrigation techniques. When irrigation is necessary, efficient water use is very important. Irrigation systems that optimize water usage such as drip systems or soaker hoses are (relatively) inexpensive and readily available. They apply water only in the immediate vicinity of their placement (usually close to the root system of a plant) and do not expose water to the air, which tends to promote evaporative loss. In contrast, overhead sprinkling is less efficient both from the standpoint of water placement and evaporative loss. If an overhead system is the only means of irrigation available, then watering early in the morning will help to conserve water.

The amount of water that should be applied when irrigation is necessary is an important consideration in water-wise gardening. The old adage “to water thoroughly but infrequently” applies well to water-wise gardening. When irrigating, sufficient water should be applied to have the top six inches of soil moist (but not soggy) for a few hours after the irrigation system has been shut off. Soil type along with delivery rate will dictate the amount of time an irrigation system must be operated to accomplish this goal. With all irrigation systems, runoff reduces water-use efficiency. Since water runoff is greatly influenced by the physical property of the soil, the need for proper soil improvement before planting becomes of even greater importance.

In conclusion, water is the natural resource that ultimately will dictate Earth’s population. The summer of 2012 appears destined to be one of the driest in recent memory and is a good object lesson that water-wise gardening should be a way-of-life for all gardeners. By following the practices outlined above, gardeners can produce attractive, colorful landscapes while at the same time conserving our most valuable natural resource.