While water is essential for all plant growth, it is not always uniformly available or distributed when and where the plant needs it. Therefore, supplemental water is often needed to sustain and support healthy plant growth whether it's vegetable plants, annual flowers, trees and shrubs or lawn grasses. Picture 1. For most of us, that means getting out sprinklers and hoses and watering on occasion. There are also automated systems available to aid in the distribution and convenience of supplying supplemental water to lawns. Following are some watering practices beneficial to lawns that can help minimize unintended, negative environmental impacts.
Water friendly lawn care practices anyone can implement
- During the hot and dry summer months, lawns will need about an inch of water per week including rainfall to remain green and growing. One inch of water per week may be sufficient for two weeks or longer during the cooler periods of spring and fall. Always remember to factor in the amount of water received via rainfall so as not to be applying more water than the plant needs or can use.
- Adjusting watering practices seasonally is necessary. In the spring and fall when roots are active and deeper in the soil, larger amounts of water can be applied per application but with longer periods of time between watering. In summer, more frequent watering is necessary due to shallower rooting depths. Shallow but more frequent application of water DOES NOT MEAN that the soils should remain saturated with water. (See the following section on the various problems associated with waterlogged lawns and soils.) Some soil drying between watering is beneficial for the plant. Slight moisture stress experienced by the plant will encourage rooting.
- When irrigating, avoid excessive amounts of water that may cause puddles on the surface of heavier clay soils. See Picture 2. Moreover, too much irrigation on sandy soils leads to the water moving past the root system increasing the likelihood that nutrients being carried with the water will potentially contaminate groundwater.
- Water early in the morning when temperatures are cool and winds are light. This puts more water into the lawn for grass plant use and less lost to evaporation.
- Mow grass plants higher (3.0 to 3.5 inches) especially during the summer to encourage a deeper, more robust root system. See Picture 3. Deeper roots can access greater supplies of water and nutrients in the soil. In other words, lawns mowed higher will better tolerate the warm and dry conditions of summer. When supplemental water is needed, it is often on a less frequent basis ultimately conserving water.
- Core aerifying compacted soils will: improve water infiltration, reduce runoff, increase rooting and access to soil nutrient and water reserves.
- Take advantage of irrigation system rain sensors and/or soil moisture sensors. These will prevent automatic systems from turning on during periods of rain or when there is already enough moisture in the soil.
Be careful not to keep your soil too wet!
Photo 4: Creeping bentgrass taking over in an excessively moist Kentucky bluegrass lawn. Bob Mugaas.
Never allow the surface soil to remain water saturated (i.e., waterlogged), even for short periods of time. See Picture 2. Healthy grass root systems need soils with equal parts water and air. Air in the soil pore space is required for both nutrient and water uptake. Too much water forces air out of the pore spaces creating a waterlogged condition. This yields root dieback and a shallow root system making plants more vulnerable to a number of serious plant stresses and diseases.
Other issues and problems associated with overly wet soils.
- Excessively wet soils can contribute to undesirable development of thatch (greater than ¾ inch or more). Excessive thatch is associated with poor stress tolerance and increased disease and insect problems.
- Soils that remain wet are often invaded by grassy weeds, which can be difficult to control once established in a home lawn. Examples include annual bluegrass, rough bluegrass, creeping bentgrass and yellow nutsedge. See Picture 4. Also, moist shady areas can be invaded by moss. This is another difficult plant to control unless the environmental conditions can be changed to not favor moss growth. Conversely, lawns that are allowed to dry somewhat between watering rarely have even minimal problems with any of these weeds.
- Research studies have shown that when additional water is applied or falls on already waterlogged soils, there will be an increase in the amount of runoff volume and potential nutrient loss under those conditions.
- During warm summer conditions, waterlogged soils can significantly increase the loss of fertilizer nitrogen back to the atmosphere in the form of nitrogen gas. Likewise nitrogen carried in water moving down through the soil past the plant's root system can also be accelerated. In either case, this can end up wasting the fertilizer applied and potentially contaminate ground water.
For more information regarding proper lawn watering practices, check out the Lawn Watering chapter of the Sustainable Urban Landscape Information Series at the U of MN Extension website.