Poa annua

Poa annua thrives in mild, temperate climates with high moisture availability. Poa annua grows best in temperatures between 60 F and 75 F. It germinates when soil temperatures are consistently below 67 F and adequate soil moisture is present. It is the most common putting surface in the northern United States and can grow equally well as a monostand or in a mixed stand with creeping bentgrass. Fine texture, dense growth and the ability to provide a smooth putting surface are what it is known for.

Poa annua has a vast and diverse set of genes, which gives it the unique ability to adapt to its environment by expressing different parts of its DNA based on environmental pressure and what gives it the best competitive advantage. Additionally, Poa annua can seed at very low mowing heights, so those advantageous traits are passed on to their offspring, further refining the high-performing local “ecotypes” of Poa annua many older golf courses are known for having on their greens. It also gives some peace of mind knowing a large seed bank is available in the soil ready to fill any unfortunate voids that may occur. While not a stand-alone reason to select Poa annua, adaptability and high seed production are certainly a feature of the grass.

It is said that the best Poa annua putting greens are like that now because decades of intensive management have modified the biotypes present. This is important to note since this is likely longer than anyone is willing to wait for excellent Poa annua greens. Poa annua’s ability to evolve makes it better able to withstand low mowing, repeated rolling and traffic. This sounds excellent but again, this process takes decades, likely longer than anyone is willing to wait for excellent Poa greens. If high-quality Poa annua greens are being expanded during a project and the course intends to keep Poa annua as the primary putting green turf, establish a nursery with cores from the existing greens to make expansions that will match in appearance and performance.

With all that being said, Poa annua has several limitations including susceptibility to disease and environmental stress like extreme cold and heat, and seasonal seedhead production. None of the challenges are insurmountable, but they are significant enough to factor in the decision-making process.

Key Characteristics:

• Fine leaf texture and high shoot density
• Adaptability to frequent mowing at low heights (below 0.100 inch)
• Excellent ball roll and speed when seedheads are properly managed
• Rapid colonization and natural presence on many golf courses
• Higher water and nutrient demands than bentgrass
• Prone to disease (e.g., anthracnose, summer patch, dollar spot and snow mold)
• Struggles in extreme heat and drought conditions 
• More susceptible to various forms of winter injury than bentgrass
• High traffic tolerance
• More shade tolerant than creeping bentgrass
  

Creeping Bentgrass

Creeping bentgrass is a perennial cool-season grass widely used for putting greens in cool and transition zone climates. When maintained at a high level it has a dense, upright growth habit with a smooth, uniform playing surface. Bentgrass is favored for its tolerance to close mowing and ability to recover from wear and tear. It is generally considered a stronger, more-resilient grass than Poa annua with regards to summer and winter survival. Plant breeding has focused on creating new bentgrass varieties with improved heat and drought tolerance. Breeding has also focused on improved leaf texture. Frankly, the goal has been to make leaf texture more like Poa annua! Improved bentgrass varieties are readily available for purchase as seed or sod, so you should not have an issue getting the bentgrass you want.

Key Characteristics:

• Fine leaf texture with high shoot density
• Tolerant of low mowing heights (around 0.100 inch)
• Provides a smooth, fast putting surface with consistent ball roll
• Can tolerate colder temperatures and longer durations of ice coverage than Poa annua
• Less prone to weed invasion because of its density during times when weeds typically germinate 
• Requires careful management to prevent thatch accumulation
• Vulnerable to heat stress, take-all patch, dollar spot and Pythium diseases
• Requires precise water management, but is more drought tolerant than Poa annua
  
  

Factors Influencing the Choice Between Poa annua and Creeping Bentgrass

Climate and Environmental Conditions

The local climate plays a significant role in determining which grass will perform better on a given course. This is a fairly obvious statement, but the decisions get complicated in many areas because both grasses may grow equally well but not necessarily at the same times of year or during common variations in weather. Growing environments also have a role in determining which grass to choose. If your course is heavily wooded, Poa annua is the better option. Conversely, in wide open environments creeping bentgrass will perform better.

In general, Poa annua thrives in regions with moderate temperatures, but will require more fertility, water and plant protectants at times. During periods of stress for cool-season greens, defensive maintenance practices will typically be required earlier with Poa annua than creeping bentgrass. Poa annua is also more vulnerable to winter injury than creeping bentgrass, which is a significant consideration in northern parts of the U.S. and into Canada.

Creeping bentgrass performs well in cooler climates and can be pushed farther south into the transition zone than Poa annua, but in hot and humid conditions it requires careful management. Historically, creeping bentgrass is more tolerant of challenging summer weather than Poa annua, but “puffy” turf during high humidity leads to slower green speeds and reduced surface smoothness. Bentgrass is less shade tolerant than Poa annua, so planting bentgrass near trees that can’t be removed could lead to suboptimal conditions. With that said, both grasses perform better in growing environments that offer plenty of light and air movement.

Maintenance Requirements and Costs

Both grass species require intensive maintenance to deliver quality putting green conditions, but differ in their specific needs. Poa annua requires frequent product applications for seedhead suppression and disease control, and more-frequent watering and fertilization. Creeping bentgrass requires more aeration, vertical mowing and sand topdressing to manage thatch and reduce disease pressure. The Green Section Record articles “The Ins and Outs of Managing Poa annua Putting Greens” and “The Ins and Outs of Managing Creeping Bentgrass Putting Greens” go into great detail on the specifics of successfully managing each of these grasses on putting greens. In lower-budget scenarios, bentgrass is arguably more durable but is also very likely to be invaded by Poa annua over time, so the most likely outcome is a mixed stand, which is very common and can still deliver perfectly acceptable playing conditions.

Playability and Performance

From a golfer's perspective, both grasses can provide excellent putting surfaces, but there are key playability differences. Poa annua tends to produce a very firm and fast putting surface, particularly in dry conditions. The presence of Poa annua seedheads in the spring – and at other times of year in some locations – can slightly disrupt ball roll, whereas creeping bentgrass typically maintains its speed and smoothness throughout the playing season.

Golfers often have strong preferences for one grass or the other – but those opinions are not always based on facts or what is truly possible at a particular course. If you happen to play in an area with a high percentage of well-maintained Poa annua greens, golfers may believe it is the superior surface simply because of who has them. Some of the world’s top golf courses, including Pebble Beach and Oakmont, feature Poa annua greens due to their texture and playability and the suitability of Poa annua in their climates. However, these are facilities with significant resources available.

Disease and Pest Resistance

Disease management is a critical factor in turfgrass selection. Poa annua is highly susceptible to anthracnose, snow mold, summer patch and dollar spot, which means it requires an aggressive and expensive fungicide program. Annual bluegrass weevil is also problematic in Poa annua greens and collars. This is currently one of the most expensive pests to control.

Creeping bentgrass is prone to dollar spot, take-all patch (especially on new greens), and Pythium blight. These diseases can generally be managed with preventative fungicide applications, proper aeration and irrigation practices, and newer bentgrass varieties that are more resistant to diseases like dollar spot. New varieties will still require a comprehensive plant protectant program, but depending on weather conditions there will be opportunities to stretch application intervals and save money. In a climate with extremely high disease pressure, like the transition zone, I would typically recommend bentgrass options.

Tolerance of Mowing and Traffic

Both Poa annua and creeping bentgrass tolerate low mowing heights, which is essential for putting greens. Anecdotally, I think Poa annua can tolerate a lower height of cut than bentgrass but that doesn’t mean mowing lower is necessary to provide good conditions. From a championship and daily play perspective, both can tolerate the same low mowing height if needed, so this is not a significant differentiator.

Poa annua exhibits excellent wear tolerance and recovers quickly from damage, making it more resilient than bentgrass under high-traffic conditions. Some courses also choose Poa annua over bentgrass because of winter traffic and shade. If you plan to play on the greens during winter, or if shade is a concern at any time of the year, Poa annua is better – albeit marginally. Considerations like this make Poa annua a popular option in places like the Pacific Northwest, where shade issues, cloudy and damp conditions, and play during winter all favor Poa annua over bentgrass.

Preferred aeration timing can influence grass selection also. If your course aerates in very early spring and/or very late fall, Poa annua encroachment is more likely to occur in bentgrass greens. However, this also means that if you maintain Poa annua as the primary grass you can extend the window for aeration. Creeping bentgrass should be aerated when it is actively growing for quickest recovery and to minimize potential Poa annua invasion. This is often late spring/early summer and late summer.

Many golf courses that start with creeping bentgrass greens find that Poa annua naturally infiltrates over time. Mowing at ultra-low heights and performing aggressive surface management practices can contribute to Poa annua encroachment due to its adaptability, prolific seeding and wear tolerance. Fertility practices, water management and growing environments can also play a role in Poa annua encroachment. The risk of encroachment is an important consideration. If you argue for bentgrass greens and it only takes a few years before they have large populations of Poa annua, that may not be well received by golfers and decision-makers. There are more tools available today to control Poa annua in bentgrass greens, but there is a very good chance your maintenance team will spend time handpicking Poa annua plants if the intent is truly to keep the greens predominantly bentgrass. Not every course has the resources to manage Poa annua invasion effectively, so it’s important to set realistic expectations or simply choose to stay with predominantly Poa annua greens if those are working for your facility.

Water and Fertilization Needs

Poa annua often requires higher moisture levels than creeping bentgrass to maintain optimal performance, but can become susceptible to root rot and other diseases if overwatered. Creeping bentgrass also requires consistent irrigation, especially during stressful parts of the summer, but it requires less watering than Poa annua. It performs better with deep, infrequent irrigation because of its naturally deeper and more-fibrous root system.

From a fertility standpoint, producing high-quality Poa annua putting greens will require more nitrogen than creeping bentgrass, especially the newer bentgrass varieties. Applying 3-4 pounds of nitrogen per 1,000 square feet per year is common for Poa annua, whereas 1-2 pounds of nitrogen per 1,000 square feet per year is common with creeping bentgrass. Less watering and fertilizer can translate to meaningful savings in input costs and staff time.

Which Grass Is the Right Choice?

There is no definitive “best” grass for cool-season putting greens – only the best choice for a specific course based on climate, maintenance capabilities and golfer expectations. Superintendents will hear opinions from golfers about the two grasses based on what other courses have, but site conditions, maintenance resources and amount of play can all be significantly different even among courses in close proximity. Knowing that comparisons from golfers are likely, it is even more important for the superintendent to do their due diligence so that they can weigh the options and present a fact-based case for the facility.

Many courses with high Poa annua populations in their greens choose to embrace it rather than fight it, even when renovation presents an opportunity for converting to bentgrass. There is also a new seeded variety of Poa annua bred for improved characteristics that make it a good choice for courses looking to improve their Poa annua greens without waiting for natural selection to work its magic. Conversely, new courses typically use bentgrass for its maintenance and playability advantages and because there are simply more seed and sod options available. They may try to keep their greens predominantly bentgrass or expect eventual Poa annua invasion and plan to maintain a mixed stand. There are also plenty of courses that have predominantly Poa annua greens that switch to creeping bentgrass for improved disease resistance and/or better tolerance of extreme cold or heat. Ultimately, the decision between Poa annua and creeping bentgrass should align with your course’s environmental conditions, available resources, and long-term maintenance strategies to provide golfers with the best possible playing experience.