Julie Weisenhorn, Director, University of Minnesota Master Gardener Volunteer Program &
Kathy Zuzek, University of Minnesota Extension Educator
Watering your garden and lawn ... it seems so straight forward. When the soil is dry or a plant wilts water. If it doesn't rain for two weeks, water. If you happen to have the hose on, sprinkle on a little water.
Not so. There are many factors -the type of soil and the amount of sun and wind in your yard, the types of plants that you grow, weather patterns, and your cultural practices - that play into a landscape's water needs. The water-wise gardener considers and plans for these factors to produce beautiful landscapes while minimizing water use.
Study your Yard
Let's address the soil first. Knowing your soil type - sandy, loam, clay - is the most important factor when determining how much and how often to water. Having your soil tested at the University of Minnesota Soil Test Lab (www.soils.umn.edu) is a reliable, easy, and inexpensive way to find out what kinds of soil your yard contains. On one end of the soil spectrum are sandy soils with their large particles that allow water and nutrients to drain and leach away quickly, leaving you with a low-fertility soil that dries out quickly. On the other end are clay soils with their small particle sizes packed so closely together that there is little space between particles. As a result clay soils are prone to poor drainage, low air porosity, and compaction. It is not hard to figure out why sandy and clay soils are often called "problem" soils and that sandy soils will need more frequent watering than clay soils.
Adding organic matter- compost, peat moss, composted manure - will do wonders to improve the water-holding capacity of both sandy and clay soils. Compost-amended sandy soils will do a better job of holding on to water and nutrients. In clay soils, compost will improve the arrangement of all of the small particles, increasing the air space, so that oxygen is more available to plant roots and water drainage improves. With both soil types, adding compost improves the balance of water, oxygen, and nutrients in the soils, making it easier to grow healthy plants with lower input from you the gardener. For more information on soil amending and compost please visit http://www.sustland.umn.edu/implement/amending_soils.html
The light levels in your yard - full sun, partial shade, or full shade - and your yard's exposure to wind affects the moisture level of soils and how often you have to water plants. Sunnier and windier sites will need more frequent watering that more protected and shadier sites.
Right Plant for the Right Place
As you design your gardens and browse through your favorite garden center, remember to pick plants that will grow well in the soil types and light levels of your yard. If you want to minimize watering or have sandy soils, choose plant varieties such as sedum and low bush honeysuckle that tolerate drier conditions and require less water. Plants like turtlehead and red-twigged dogwood that prefer moist soil areas would do poorly under dry conditions.
Remember that some plants do well in full sun, others in partial or full shade. Attractive companion plantings chosen both for visual appeal and common water and light requirements will produce the healthiest and most beautiful landscapes while minimizing water requirements. For more guidelines about plant selection, visit the University's website Sustainable Urban Landscape Information Series (SULIS) at www.sustland.umn.edu.
Water-wise Cultural Practices
It's planting time. Spacing of plants plays a role in watering needs too. Placing plants too closely together will increase the competition between the plants for resources such as water and nutrients. Be sure to space plants based on their mature size, allowing them to grow to their full potential above and below ground to minimize plant stress.
Organic mulches - wood chips, shredded bark, pine needles, straw, grass clippings, shredded leaves - are great tools for the water-wise gardener.
A three- to four-inch layer of mulch over a garden buffers soil temperatures and serves as a barrier that slows the rate of water evaporation from soil into the air. The net result is less fluctuation in soil moisture and more water available to plant roots, which improves root growth while reducing irrigation needs. In addition, as organic mulches break down, they add organic matter to soils, improving the water-holding capacity of soils.
Mulches discourage weed growth in our gardens, eliminating the competition for water between our landscape plants and weeds.
Woody plants and turfgrass don't coexist well. We have all struggled to keep sun-loving grass varieties alive under the canopy of a tree. But with their density and close proximity to soil surfaces, turfgrass roots enjoy a competitive advantage when they cover tree and shrub roots, and siphon off vast amounts of water. This is an even bigger problem during periods of drought, creating a double dose of stress for woody plants. Replacing turf around trees and shrubs with an organic mulch eliminates all of these problems and reduces irrigation needs - no more pouring water on grass struggling to grow in shade, no more grass roots stealing water from roots of woody plants, and less evaporation of water from mulched soils around trees and shrubs. For more information on mulching, visit http://www.sustland.umn.edu/maint/mulching.html.
How about watering our plants efficiently to conserve water? Efficient irrigation means applying water in the proper amount and only when it is needed.
How do you know when you should water? As a rule of thumb, water infrequently but do water before plants wilt. When you do water, give plants a deep thorough soaking. Frequent, shallow watering causes plants to produce shallow root systems that cannot survive the heat and dry conditions of mid-summer months. Watering deeply and infrequently causes plant roots to grow deeply into the soil in search of the water, resulting in deeply rooted, more drought-resistant plants. Remember that sandier soils, higher temperatures and wind velocities, periods of drought, and recently-planted gardens all require increased watering.
Watering in early morning when evaporation rates are low conserves water.
Applying water at the root zone of plants either by hand or through drip irrigation is another water-wise practice. Drip irrigation is the slow application of water directly to the plant's root zone using emitters spaced along tubing lying on the ground. Water is absorbed slowly and more deeply into the soil and root zone, helping to maintain the right balance of water and air in the soil while promoting deeper root growth. No water is wasted on non-growth areas, evaporation is reduced, and runoff and wind-blown water is avoided, making drip irrigation a great water conservation practice. For more information on drip irrigation, visit http://www.ext.colostate.edu/pubs/garden/04702.html and http://www.dripirrigation.com/drip_tutorial.php
How efficient are automated sprinkler systems? The design of an automated sprinkler system determines its efficiency. But an efficient irrigation system can still waste water if it is programmed to run too often or too long. Initial programming and seasonal adjustments to the program of an automatic sprinkler system should be based on the type of plants you are growing and their water needs, soil type, seasonal temperatures and moisture levels, and exposure of your site to light and wind. Adjusting your sprinkler's programming seasonally both conserves water and improves plant health by matching water applied to plants' needs.
Rain sensors incorporated into your automated irrigation system are another water-conserving tool. Automatic rain shut-offs turn controllers off when there is sufficient rainfall. Your controller's manual override will do the same thing, but for people often away from home, rain sensors are a great alternative. For more information on efficient irrigation and home irrigation systems, please visit http://www.ext.colostate.edu/PUBS/Garden/07239.html