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Annual Bluegrass

This grassy weed (also called winter grass, poa annua, speargrass) is capable of growing at mowing heights as low as 1/4". It thrives in cool, moist weather even in damp, shaded areas. It produces hundreds of whitish green seed heads at any mowing height. Because of its tolerance to close mowing and seed head formation, it is especially difficult to control.

Studies have shown that the annual bluegrass seed can even germinate in total darkness. The Achilles heal of this weedy pest is that it is a very shallow rooted and therefore needs water on a regular basis. However, because of Its shallow roots, it can tolerate compacted soils making the grass able to survive in areas where regular turfgrasses struggle.

Annual Bluegrass Photo

Annual bluegrass has "boat-shaped" leaf tips that curve up like the bow of a boat. It tends to grow in small clumps and seldom reaches heights over 10".

Annual bluegrass summary:

  • Winter annual or biennial

  • Reproduces by seed and stolons that root at the nodes

  • Leaves are about 1/2" - 3/4" long

  • Annual bluegrass occurs on wet, compacted soils and in cool temperatures

Efforts to find chemical controls for annual bluegrass have been thwarted by its diverse genetic make-up. It is officially described as a cool-season winter annual. Winter annuals are plants that germinate in late summer to early-fall, overwinter, and produce seed in the spring. Typical winter annuals die soon after seed production as daytime air temperatures increase.

Non-chemical treatments

  • Since annual bluegrass is shallow rooted, avoid watering it during extended dry periods as seen frequently in late summer. Desirable turfgrasses will survive longer dry periods that the annual bluegrass will not survive.

  • Aerate compacted soils regularly so that desirable turfgrasses can better survive.

  • Over seed infected areas in the spring and fall.

  • Reduce or eliminate fertilization in the spring