Bob Mugaas, UMN Extension Educator - Horticulture
Minnesota lawn grasses are known as cool season grasses as their peak periods of growth and activity occur during the (usually) cooler seasons of spring and fall. These grasses include Kentucky bluegrass, fine fescue, perennial ryegrass and tall fescue. The middle of May through most of June is the prime flowering period for these cool season grasses in Minnesota. Kentucky bluegrasses tend to be the first of the grasses to begin flowering with the fine fescues, perennial ryegrasses and tall fescue coming on slightly later. See Picture 1 of Kentucky bluegrass flowering.
In most instances, even if we are regularly mowing the lawn, these shoots continue to elongate in an attempt to produce their flower cluster known as an 'inflorescence'. See picture 2. The result of mowing regularly is that we often do not see the fully elongated flowering stem
Of course, not all of the shoots present in a lawn will have gone through the biological changeover to a flowering 'bud' the previous fall. Hence, our lawns have enough growing shoots present, even though the lawn may be a little thinner, it still looks and functions like a lawn. Also, by the time we get to early August, a new round of grass shoots will be starting to form along with the production of new leaves, rhizomes, tillers and roots. This growth will continue through the fall period when once again grass shoots with sufficient biological maturity will make the changeover to flower buds that will again produce next spring's flowering shoots.
Because these flowering stems temporarily disrupt the otherwise uniform appearance of a healthy lawn surface, their presence is often viewed unfavorably. The important point here is that grass flowering is a normal, temporary condition common to most lawns. There really is little that we can control within this naturally occurring process. If desired, mowing slightly shorter for a couple of times to remove more of the inflorescence can make the flowering stems less apparent. Also, increasing mowing frequency for 2 to 4 weeks during peak flowering will help keep flowering stems from becoming too visible and disruptive. However, since flowering occurs just before the warmer and drier parts of the growing season, it will be important to raise mowing heights back up as soon as possible to encourage as much root growth and rooting depth as possible before those more stressful conditions settle in.
On the flip side of the grass flowering question is whether or not any of seed produced will actually provide some 'reseeding' back into the lawn. In other words, if one lets their lawn go to seed will they receive some benefit from the seed produced in terms thickening up the lawn. The short answer to that question is usually not. Since the process of mowing continually cuts off the developing flower cluster, any seed that starts to develop doesn't reach sufficient maturity to actually be viable. In an unmowed situation such as would be the case in a seed production field, the flower stems are allowed to fully ripen, turn brown and dry. The seed is then harvested just before it has a chance to naturally disperse from that dried flower cluster. That harvesting usually occurs from mid to late in June to perhaps early July.