Bob Mugaas, University of Minnesota Extension Educator
Early May usually finds most Minnesota lawns well into turning green and in need of a first mowing. Remember that the early part of the grass growing season, late March through the first part of May, is when our lawn grasses produce the best root growth of the year. Therefore it is important to not be mowing too short as shorter mowing heights reduce the amount and depth of those roots. Maintaining an average mowing height for around 2.5 to 3.0 inches, even at this time of year, is appropriate. Those larger, more robust root systems are important in providing the plant with the necessary water and nutrients to sustain the plant through flowering and increase the plants ability to withstand summer stresses.
For average home lawns consisting primarily of Kentucky bluegrass and growing in sunny conditions, early May is a good time to apply that first application of fertilizer. Usually this will coincide with about the time you plan to mow for the first time. This will be especially true if there was no fertilizing done the previous fall. It’s best to apply about ¼ to ½ inch of water following the fertilizer application to help it dissolve and move into the soil where it will be less apt to runoff and be available for plant roots to take up.