Know Your Turf: Annual Bluegrass

Know Your Turf seeks to improve the reader’s understanding of the turf aspects of the golf course. Each post will explore and explain the uses of a species of a turfgrass in a golf course setting and how the management of that species influences the game. The majority of the information presented is from my own turf education and the purpose of these posts are to educate and inform, with no ambition to be authoritative. I encourage comments, suggestions and corrections in the comments section. Further information can be found at the Michigan State University USGA Green Section Archive and other turfgrass sources.

No species of turfgrass invokes more polar opinions than Annual bluegrass, commonly referred to by it’s scientific name Poa annua, or simply as Poa. Annual bluegrass suffers from a large amount of bad press in the golf agronomy field that is largely undeserved. However, the large majority of golf courses in the country have putting surfaces comprised mainly with Annual bluegrass including: Oakmont, Pine Valley, and Bethpage Black.

Species Overview

Annual bluegrass (Poa annua) shares a genus name with other Bluegrass species such as Kentucky bluegrass (Poa pratensis) and Roughstalk bluegrass (Poa trivialis), both of which are found in many golf course applications. While technically correct, referring to Annual Bluegrass as simply “Poa” is ambiguous at best, and such usage of the term has perhaps contributed to the black mark Annual Bluegrass has as a turf.

The plant is identified easily by the boat-shaped tip of an uncut leaf. This is unique amongst most turf found on putting greens. Annual bluegrass appears in non-uniform stands as bunches of lightly colored turf growing relatively upright compared to the turf (usually bentgrass) around it. The plant persists in high traffic and shaded areas on putting greens where other turf is grown, especially in areas frequently used for hole locations. In fairways, Annual bluegrass is often found in areas where surface water drains or in areas frequently pockmarked with divots.

In general, Annual bluegrass is a cool-season plant (C3 pathway for respiration) with an annual life cycle that produces viable seed after overwintering. The seed sits in the thatch and germinates in the fall. The plant then overwinters before repeating the cycle again. Seed production is most noted by golfers in the mid-Spring as the putting surfaces comprised of Annual bluegrass become bumpy and puffy as the short seedheads flower.

Annual bluegrass has a bunch growth habit, which means several leaves tiller from one initial crown without the development of extensive stolons or rhizomes. This growth habit mitigates the development of grain on the greensward. As such, Annual bluegrass generally relies on seed to perpetuate itself though proper conditioning can develop a reliance on vegetative methods of propagation.

While comprised of many biotypes, two are noteworthy in golf course applications. Poa annua reptans demonstrates a more perennial nature developed through selective pressure from use on putting greens. Because of this perennial nature, Poa annua reptans is capable of developing a limited stolon structure and produces limited seedheads in the Spring. The second biotype, Poa annua annua, is mostly found on the golf course with Annual bluegrass that germinates in early spring in bare, or compacted turf. Seed is produced by this type all season when conditions dictate and the type comes under severe stress during the heat of the summer – rarely surviving. The seed from this biotype can persist in the soil for up to six years.

Golf Course Applications

Arguably, Annual bluegrass is the most suited turf for the closely-mown areas found on the golf course. The high tolerance of low heights of cut, bunch growth habit, and persistent nature of its propagation methods allow for a turf manager to provide a smooth, fast and easily recovered putting surface under ideal conditions. The issue arises in finding these ideal conditions and it is only in the extreme northern climates that Annual bluegrass will survive the summer stresses without considerable assistance from turf managers.

Annual bluegrass is found in all areas of the golf course from putting green to low-maintenance rough. Annual bluegrass selected for tee and fairway areas present considerable demands on the turf and turf managers, especially with water and other resources during the high-heat of the summer. Golf courses with high traffic will find considerable difficulty in keeping large areas of the plant alive during these conditions. While under considerably more stress during the heat of the summer than fairways or tees, the localized nature of putting greens (typically three to five acres for an eighteen holes with a practice facility) make for a more economic use of Annual bluegrass as the resource requirements are limited to a smaller portion of the golf course.

Why the black mark?

The stigma against Annual bluegrass comes from the difficulties in maintaining the turf through the summer. As soil temperatures increase, the plant loses root density and the ability to take in water and other nutrients. Furthermore, the C3 respiration pathway becomes extremely inefficient at air temperatures exceeding 88 degrees F. In order to mitigate these natural setbacks, a turf manager must constantly cool and irrigate the plant in order to keep it alive. Such frequent irrigation not only diminishes the golf course’s playability but also taxes the soil structure, requiring cultivation efforts such as topdressing and aeration that further hamper playability during times of cooler temperatures in the spring and fall.

However, in the century or so since turf research first produced reliable data, turf managers have developed many effective techniques in mitigating golfer pain with regard to maintenance of Annual bluegrass as a golf turf. While seasons like the summer of 2010 still present large challenges to turf managers, Annual bluegrass has become a manageable turf in the same traditional climate zones as other cool-season turf, such as Creeping bentgrass. Research and practice in maintaining Annual bluegrass as a putting surface will further serve to remove the stigma of Annual bluegrass as a desirable putting surface.