All of the commonly used turfgrasses – Kentucky bluegrass, perennial ryegrass and tall fescue – will flower and attempt to produce seedheads in spring. There is not much that can be done to prevent flowering and seedhead production in lawns (plant growth regulators are used on golf course turf for this purpose). It is largely a function of turf variety (some varieties naturally flower more than others) and spring weather conditions.
Cool spring weather can prolong the flowering period. Sustained, hotter temperatures will soon halt flowering and seedhead production and cause annual bluegrass to die out. One common weedy grass that is quite visible due to its light green color when it is flowering is annual bluegrass (Poa annua).
Flowering and seedhead production can detract from the appearance of turf leading homeowners to believe that a weedy grass has invaded. Due to their tough, fibrous nature, the flowerstalks are difficult to mow cleanly. Shredded flowerstalks left behind first turn white or grey and later tan. Lowering the mowing height will not eliminate flowering and is likely to stress the turf. As seedhead production peaks, the turf may start to look stemmy and less dense. This is because any individual grass plant that produces a seedhead dies. Fortunately, only a small percentage of plants in a lawn will enter the reproductive stage in spring, so turf density will return quickly if the lawn is properly mowed, fertilized and irrigated.