ISSUE  10   July 12, 2007


Questions on how to care for lawns (particulary Kentucky bluegrass types) during hot, dry weather have been answered by the NDSU Plant Diagnostic Lab. Several samples of turf from early May were suspected to have suffered from drought stress from the previous year. We suspect that these homeowners did not provide any supplemental water during the long period of hot, dry weather conditions in some parts of the state last year. The prolonged dry period in Fargo this year has ended with recent showers, but prior to these showers, area lawns were showing water stress. Even though the cool-season grasses predominantly grown in North Dakota become dormant during hot weather, they still require water to survive, contrary to some long-held beliefs. No water on dormant grass during hot, dry periods, particularly on sodded lawns, can lead to dead grass and poor recovery. The general recommendation is to provide turf about one inch of water per week, even during hot, dry weather. The actual amount of water may vary from this general guideline, depending on the number of trees or other plants competing for the moisture, thickness of the thatch layer, disease, clay content, level of compaction, and other factors, so adjust your watering needs accordingly.

Watering in the morning hours is usually best for at least two reasons: 1. less water is lost to evaporation (compared to watering in the heat of the day), and 2. foliage is exposed to fewer hours of wetness (prolonged leaf wetness favors development of foliar diseases). If you who do not have an automated sprinkler system and are typically rushed in the morning (like me), morning watering may not be practical. So against my better judgement, I normally water during evening hours. This practice puts my lawn at risk for disease development, but I balance that risk (I hope!) by watering less frequently, about once per week during dry periods. For most lawns seeded to Kentucky bluegrass, applying about 1 inch of water during dry periods once a week is sufficient. If your lawn has a weak root system, which is the case for most sodded lawn samples I receive in the diagnostic lab, an application of -1 inch of water twice weekly is beneficial.

If you water your lawn, you can measure the output of your spinklers by placing several Solo cups around the lawn and measuring the depth of water after a period of time (say, 20-40 minutes). If the depth of water is greater than 1 inch, you are probably overwatering, especially if you have little thatch and few trees competing for the water. It is seldom necessary to run most sprinklers for more than 20 to 60 minutes. In the interest of conservation, it is a good idea to measure your water output to avoid the expense (both financial and environmental) of over-watering.

If you choose not to water your lawn during drought periods, be prepared for thinning or general decline, although some grasses may handle drought stress better than others. If you do notice decline as a result of not watering during dry periods, over-seeding (broadcasting seed over the existing grass and raking the seed so it contacts the soil) can fill in thin areas.

The following link brings you to a website that lists NDSU publications on lawn care and related topics:  

Kasia Kinzer
NDSU Plant Diagnostic Lab

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