What Is Annual Bluegrass?

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bluegrass in lawn

Annual bluegrass (Poa annua) is a member of the grass family, just like most types of grassy weeds. It is a cool-season annual plant that is well adapted to Kansas City's moderate climate. Homeowners in our area are often a bit confused as to whether annual bluegrass is a turfgrass or a weed, so the Heartland team wants to share our knowledge with you! This post will help you understand everything you need to know about annual bluegrass in your lawn, and be sure to read our guide to grassy weeds for even more information on how you can keep your turf healthy!

Identifying Annual Bluegrass

annual bluegrass up close

Before getting into more intricate details about annual bluegrass, you must first understand how to properly identify it. Annual bluegrass looks identical to many types of turfgrass, especially before it matures and develops a seed head. It has narrow, light green blades that are slightly hairy or completely smooth, which roll up in the heat of the day. This rolled or "canoe" shape is one of the most reliable indicators of annual bluegrass, as it will likely differ from many types of turfgrass. Spotting bunches or clumps in your lawn that appear lighter and more narrow than the surrounding grass is a good place to start when trying to identify annual bluegrass.

This grass weed grows between 6 and 12 inches tall at a much quicker rate than most turfgrass. The seed heads of annual bluegrass are very fine and delicate, often appearing feathery or as if they have been made out of cotton. These seed heads tend to be white or faintly light green in color, and they will appear on the plant in mid-to-late spring. Seed heads of annual bluegrass are unsightly in a lush lawn, making them easy to spot for treatment. However, seeds will not be produced until the plant is matured, which allows this annual bluegrass to go undetected until that time.

Look For These In Your Lawn:

  • Brighter/lighter color than surrounding grass
  • Taller growth than surrounding grass
  • Smooth leaves with canoe-shaped edges/tips
  • Leaves that are spread somewhat far apart
  • Feathery seed heads in bunches
  • Light green or faintly pink seed heads
  • Growth in a clumping pattern
  • Shallow, fibrous roots (when pulled out)

Is Annual Bluegrass A Lawn Weed Or Turfgrass?

What does Bluegrass look like

Annual bluegrass can be viewed as both a grass and a weed; after all, it is closely related to Kentucky bluegrass, which is one of the most commonly used turfgrasses in cool-season lawns. However, annual bluegrass is typically considered a grassy weed in the lawn care industry for a number of reasons. Annual bluegrass does not produce the same high-quality lawn you would get from other grass types. It has very shallow and weak roots that make for a low-quality and dangerous lawn for foot traffic.

When it is found growing in lawns made up of a different type of turfgrass, annual bluegrass will use its invasive and shallow roots to get first access to nutrients in the soil. Before long, an annual bluegrass invasion will result in a patchy, thin lawn full of bunches of bright green grass. In other words, annual bluegrass creates an unsightly and unhealthy mess when it invades lawns, which is the defining characteristic of a lawn weed!

Annual Bluegrass vs. Kentucky Bluegrass

identifying Kentucky Bluegrass

The closely related Kentucky bluegrass (pictured above) is a beloved turfgrass because of the lush, deep emerald color it produces in a lawn. Annual bluegrass has much narrower leaves than Kentucky bluegrass, which do not create the best appearance or feel for a lawn. The leaf blades of annual bluegrass also have the aforementioned rolled appearance, while the leaves of Kentucky bluegrass are flat. The roots of annual bluegrass are very shallow, while the roots of Kentucky bluegrass can grow up to 6 feet deep. The deeper roots of Kentucky bluegrass create a healthier lawn that can sustain and support even growth throughout the year. A further comparison of these grassy cousins is detailed below.

Annual Bluegrass

  • Annual
  • Produces a seed head
  • Lighter green color
  • Undesirable in all climates
  • Quick growth crowds lawns
  • Shallow, invasive roots

Kentucky Bluegrass

  • Perennial
  • Produces a seed head
  • Deep green color
  • Cool-season, desirable grass  
  • Grows at a normal rate
  • Deeper, healthy roots

When & Where Does Annual Bluegrass Grow?

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Annual bluegrass is a cool-season weed, meaning that it thrives in cooler temperatures. This weed will begin to germinate in late summer or early fall when temperatures begin to cool down for the year. Once soil temperatures get down to 70 degrees or below, annual bluegrass seeds will begin to germinate. From germination, the seedling will emerge in fall, go dormant during winter, and finish its life cycle the following spring, when temperatures get warmer. In late spring or early summer, annual bluegrass will flower and set seed, starting the cycle all over again for this annual grassy weed.

Annual bluegrass is commonly found in all types of turfgrass, including Kentucky bluegrass, tall fescue, and ryegrass. This weed can be found in both sunny and shady areas of a lawn, and it is common to lawns all across the country. However, annual bluegrass tends to prefer shady areas with moist soil. This weed is commonly found in areas of a lawn that have been damaged or disturbed. Compacted and patchy lawns are also commonly home to annual bluegrass, as this weed thrives in areas that see heavy traffic.

How Does Annual Bluegrass Spread?

bluegrass seedhead

Annual bluegrass spreads largely through its seed production, and those seeds can remain viable in the soil for up to 5 years. As many as 100 seeds can be produced by annual bluegrass in as little as 8 weeks. The distinctive, delicate seed head disperses its seeds very easily, which leads to many new plants starting to germinate in the blink of an eye. Pests, larger animals, the wind, and lawn care tools are just a few examples of the ways annual bluegrass can spread when its seed head is contacted. This method of expansion is what makes annual bluegrass such a nuisance to homeowners and lawn care enthusiasts.

This weed is also notorious for invading squares or strips of sod, even before the sod is laid down in your yard (which is one of the major disadvantages of sodding a lawn). If you lay down sod that contains annual bluegrass seeds, the highly invasive roots will spread all throughout the sod strips, and you will start to notice uneven turf as annual bluegrass pops up in between the edges of the sod pieces. Always be on the lookout for annual bluegrass if you choose to sod rather than seed your lawn!

How To Prevent Annual Bluegrass

scaled seed spreader

Annual bluegrass is one of the most difficult grassy weeds to control in lawns. Removing annual bluegrass after it emerges is possible due to its shallow root system, but hand-pulling annual bluegrass should be confined to small patches rather than large swaths of your lawn. The same is true of applying post-emergent herbicides, as applying too much non-selective weed killer will destroy the healthy turf in your lawn.

Always call a professional, like the ones here at Heartland Turf & Landscape, for the best prevention and control of annual bluegrass in your lawn. Pre-emergent herbicides and mulching around the yard are two excellent options for blocking annual bluegrass seeds, and these methods are most effective when applied by a professional. Keep an eye out for annual bluegrass, especially in a sodded lawn, and try to maintain a healthy lawn throughout the year with proper fertilization, overseeding, and weekly mowing. Remember, the best defense against annual bluegrass is a well-manicured lawn, so get out there and do your part to keep Kansas City lawns beautiful and weed-free!