Lush Green Yard Care Blog

What Is Annual Bluegrass?

What does Bluegrass look like

It can be difficult to detect grassy weeds in your lawn, especially ones that look so similar to your turfgrass. Without a proper understanding of what constitutes a lawn weed and what kind of damage weeds can cause, your grass will be left vulnerable to many types of invasive species that will steal valuable nutrients and resources from the soil. Thankfully, Lush Green is here to help!

To make sure every lawn in Colorado stays as healthy and vibrant as possible, we have put together this guide to help homeowners identify and prevent annual bluegrass in their lawns this summer. With a little knowledge and know-how, we are confident that everyone can maintain a lush green lawn!

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How To Identify Annual Bluegrass

annual bluegrass up close

Annual bluegrass (Poa annua) is a species of grass that is not very different from the grass you have in your lawn. In fact, in colder climates, annual bluegrass may even be sold as a turfgrass. The problem with annual bluegrass primarily comes when it finds its way into warmer climates, or when its seeds begin to germinate in lawns that consist of different turf types. When this happens, Poa annua is invasive and destructive, and there are certain ways you can identify it for treatments if you know what to look for.

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 desirable 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 bunch-type growth is a key trait of annual bluegrass that many healthy turf types do not exhibit.

It 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 cottony in both color and texture. 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
  • Faster growth than surrounding grass
  • Narrow leaves with canoe-shaped tips
  • Leaves that are spread somewhat far apart
  • Feathery seed heads in bunches
  • Light green or white seed heads
  • Growth in a bunch pattern
  • Shallow, fibrous roots

Annual Bluegrass vs. Kentucky Bluegrass

identifying Kentucky Bluegrass

Unlike annual bluegrass, Kentucky bluegrass (pictured above) is one of the most desired turfgrasses among homeowners, but the two are actually very closely related. Kentucky bluegrass (Poa pratensis) belongs to the same family and the same genus as annual bluegrass, but it is generally considered to be a much less invasive and more attractive turfgrass.

The closely related Kentucky bluegrass 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 and invasive, 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.

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

What Does Annual Bluegrass Do To Lawns?

bluegrass in lawn

Annual bluegrass can cause a variety of issues in lawns, ranging from a temporarily unsightly appearance to permanent damage. This grassy weed grows quickly and has shallow roots that make it difficult for your lawn to stay healthy or full. Annual bluegrass competes for resources and space with other grass in the area, and these shallow roots allow it to gain first access to nutrients and moisture in the soil.

As a cool-season grassy weed, annual bluegrass requires higher amounts of nutrients when its seeds try to germinate in lawns during hotter weather. Unfortunately, annual bluegrass is also able to thrive in cool-season lawns when most turfgrasses are going dormant. As a result of these factors, lawns are often left discolored, thin, and patchy due to a lack of adequate nutrition and/or space to grow.

When & Where Does Annual Bluegrass Grow?

bluegrass seedhead
  • When: Annual bluegrass 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 seedlings will emerge in fall, go dormant during winter, and finish their 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.
  • Where: Annual bluegrass is commonly found in all types of turfgrass, including Kentucky bluegrass, tall fescue, and ryegrass, and it is common in lawns all across the country. This weed can be found in both sunny and shady areas of a lawn, but it prefers partially sunny areas with moist soil. Lawns with open, direct sunlight may have a better chance of withstanding annual bluegrass because it prefers indirect sunlight. 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?

Annual weeds do have enough time to develop overly complex root systems by which they can effectively spread an invasion through rhizomes and stolons, so they have to rely on seed production and distribution. Seeds can be dispersed by things as simple as foot traffic, irrigation, wind, and more. A single annual bluegrass plant is able to produce over 100 seeds in as little as 8 weeks, and each plant can produce over 350 seeds in a single season. Once seeds are distributed, dormant seeds can stay viable in the soil for up to 5 years.

How To Prevent & Treat Annual Bluegrass

Push-seed-spreader-used-to-overseed-a-lawn (1)

Treating annual bluegrass in your lawn starts with good lawn care practices. Prevention is a more effective form of weed control than corrective measures, so make sure you call a lawn care provider to apply pre-emergent herbicides in fall, before seedlings emerge. Applying products containing bensulide, dithiopyr, and prodiamine can be effective at controlling annual bluegrass, but there are other ways to prevent the weed. Keep the following tips in mind, and be sure to call Lush Green Services for all your weed control needs in Colorado!

  • Mow High: Scalping your lawn allows annual bluegrass to gain a stronger hold and develop more seeds.
  • Water Deeply & Infrequently: Annual bluegrass loves moisture, so avoid overwatering and frequent watering.
  • Aerate In Spring & Fall: Annual bluegrass thrives in compacted soils, which can be alleviated by aeration.
  • Overseed: Applying seed to thin patches in your lawn can help your lawn stay lush, green, and ready to overpower annual bluegrass!
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