Annual Bluegrass, Poa annua L.

In nature, annual bluegrass, Poa annua L. behaves as a true annual. It germinates in fall or spring when moisture is adequate and develops quickly, often flowering six to eight weeks after germination. In the Pacific Northwest we see it most commonly as a winter annual (Fig 1). After flowering and setting seed these annual types die typically from drought and leave dormant viable seed behind to germinate when moisture again becomes available. This efficiency in seed production makes annual bluegrass a major component of the seed bank of cultivated soils. Fig 1. Perennial type annual bluegrass on left vs. annual type on right. Annual types are rare in fine turf in the Pacific Northwest. When turf managers plant turf they initiate all of the commonly used cultural practices including irrigation. Under irrigated conditions a selection process begins that encourages development of so-called perennial biotypes of annual bluegrass (Gibeault 1972). Among othe