What is Annua Poa (Annual Bluegrass)?

What is Annua Poa (Annual Bluegrass)
Annua Poa is one of the most common weeds in turfgrass, ornamental plating and gardens in the U.S. There are 2 types of Annua Poa. The annual type is more upright in its growth habit, and produces more seed than the lower growing perennial type. Annual Annua Poa tends to develop a fairly shallow root network, and needs frequent rain to flourish. 

Annua Poa vs Kentucky Bluegrass
Annua Poa has been considered to be a more grassy weed than any other type of grass. It is a lighter shade of green compared to Kentucky bluegrass. It also develops much more shallow roots. Annua Poa is also considered a weed species; unlike Kentucky Bluegrass it can survive low mowing heights of up to an inch and still reseed. On the other hand, Kentucky bluegrass is a dark green lush type of grass most desired to have in their lawn. Kentucky bluegrass also has a remarkable recovery rate from dormancy. However it is not very shade tolerant. This photo shows a lawn that has a mixture of the two types of grasses.

Annua Poa vs Crabgrass
While both Annua Poa and Crabgrass can look similar to an untrained eye, there are some key differences. Poa Annua flourishes in 65-70 degree weather, and crabgrass grows best in 80-90 degree weather. Poa Annua has thin, blade-like, and finer leaves that are green to tan in color, while Crabgrass has thicker leaves, and tends to be more low growing, causing it to appear wider and flatter. When identifying crabgrass seeds, they appear in tiny brown oval shapes almost like grains of rice. Both Annua Poa and Crabgrass have similar life cycles to where they will die off at the end of their cycle and rely on their seed to propagate. Crabgrass is extremely hearty, and can survive in full sun even with poor soil conditions, while Poa Annua will die off when it gets above 80 degrees. You can decrease both of these types of grass by consistently mowing every 7-10 days.  

Life cycle
Annua Poa is a cool-season grass, and its life cycle starts with germination in late summer/early fall. This is because it can wither and die in extreme heat and drought conditions. It continues to germinate all through the Winter as well. It germinates best when soil temperatures fall below 70 degrees Fahrenheit. It can also grow 6-8 inches if left unmowed. The seed heads will begin to form as early as 6 weeks old, and each plant can produce roughly 100 seeds in as little as 8 weeks. 

How you get Annua Poa grass
Annua Poa can occur within heavily shaded areas that are also known to be prime breeding grounds due to the shallow roots soaking up all of the moisture on the surface level. Also very compact lawns are prone to Annua Poa. You can actually spread Annua Poa when mowing the grass. The mower can spread the seeds throughout the lawn.

Disadvantages of Annua Poa
In the springtime Annua Poa is going to be a lighter color than the rest of the lawn which can be an undesirable look. It also gives the lawn a bumpy surface look. In the spring when its seed is blooming it may look like a weed in the lawn. Below is a photo of Annua Poa when blooming, it has white feathery, tufted seed heads. It can be a very hard, expensive and time consuming task to keep up with maintaining an Annua Poa free lawn.

How to treat it?
Unfortunately, no single control procedure has been 100% successful in controlling Annua Poa in turfgrass. You may use deep and infrequent irrigation to try to discourage the development of shallow-rooted Poa. You can try to withhold watering to not water the Poa as they do not survive drought. Once your desired grass is beginning to drought you can resume watering. There are certain types of products that can be slightly helpful with decreasing the germination amount. However, it is not always the best route to take economically in residential properties. You can also core aerate and overseed the lawn to try to choke out the Poa.