Bob Mugaas, University of Minnesota Extension Educator
In some areas of the state, lawns have received ample moisture this spring to maintain good growth and color while others have been quite dry; Twin Cities included. In fact, supplemental lawn watering has already begun in many areas around the Twin Cities. In most cases, it will take about 1.0 inch of water per week to keep Kentucky bluegrass lawns green and actively growing through the summer months. One question frequently asked by homeowners is “How do I know how much water my sprinkler or irrigation system is putting out?”
Photo 1: Typical oscillating sprinkler. Bob Mugaas
Determining how much water is being supplied by a sprinkler is not a complicated process. Simply place several small flat bottomed containers within the distribution pattern of a sprinkler. Tuna fish cans work well for this measurement. A simple rain gauge or two placed within the water pattern will also work so long as the gradations are close enough to measure small amounts of water. Turn on the sprinkler as you would to normally water the lawn and leave it on for an hour. After an hour, measure the depth of water accumulated in the bottom of the container. For example, if the average accumulated water in the cans were ¼ inch for that hour, then you can assume that your set-up is putting out about a ¼ inch of water per hour. Looking at the amount accumulated in each container will also be helpful in determining the uniformity of water distribution and may suggest the amount of overlap needed to ensure all areas receive equivalent amounts of water. With automated systems, place the containers within the distribution pattern and measure the amount of water accumulated after a cycle for that part of the yard is completed. This will give you the amount of water be applied for that particular cycle.
Photo 2: Black medic (Medicago lupulina). Bob Mugaas
By early to mid-June, many of our annual broadleaf lawn weeds will be starting to germinate. One of the best times for controlling these weeds is in this early growth stage before they have started to mature. Examples of our common annual broadleaf weeds include prostrate or spotted spurge, erect and prostrate knotweed, lambsquarter, redroot pigweed and purslane. The clover like plant, black medic as well as yellow woodsorrel are usually considered annuals although some plants may overwinter and behave like a biennial or short lived perennial. Taking a few minutes to walk your lawn in order to determine when some of these weeds may be germinating allows one to easily remove them by hand and/or treat them with an herbicide. Remember, removing and/or treating plants with an herbicide is much more efficient when they are small, even at the lower application rates stated on the product label.
Photo 3: Yellow Woodsorrel (Oxalis stricta). Bob Mugaas
For those sites that are irrigated, regular mowing will be required throughout the growing season. Maintaining heights at about 2.5 inches should be adequate for most home lawns. For those lawns not receiving irrigation, mow only as needed and required by the growth of the plant. Try to follow the general rule of thumb to not remove more than 1/3 of the height at any one mowing. For example if you are maintaining a height of cut at about 2.5 inches, then mowing should be done when the height reaches about 3.5 – 4.0 inches.
While most walk-behind rotary mowers adjust mowing heights by resetting the four wheels to the desired height, it is occasionally a good idea to see how close that setting really is to the actual height of cut. The easiest way to do this is to simply take a ruler and gently push it through the turfgrass canopy until it rests firmly on the lawn/ground (may not be actual soil) surface. Then look across the grass plants just in front of the ruler and see what the height is. For example, if the ground is firm then mower wheels will ride higher and consequently the height setting will more closely approximate the actual cutting height. However, where the ground is soft or there is a significant thatch layer present, the wheels will sink more deeply into the lawn and hence the mowing height is actually less than the wheel settings would indicate. In fact, where there is significant thatch present mower wheels can ride so much lower that the lawn surface between the wheels is actually scalped. Remember to take the time to adjust your mower correctly, periodically verify that the mower height settings are actually providing the desired height of cut, and always mow with a sharp blade.