Brothers Lawn Service & Landscaping

Identifying Annual Bluegrass

Annual bluegrass is a grassy weed that can cause some serious problems in lawns. This weed often masquerades as healthy turf, which is exactly why you need to know how to spot it in your lawn! Keep reading for information on how to identify and treat annual bluegrass, and be sure to call the experts at Brothers for all your weed control needs!

What Is Annual Bluegrass?

When attempting to identify annual bluegrass, there is one big question that most people seem to get stuck on: is it a weed or is it grass? After all, annual bluegrass (Poa annua) is very closely related to the popular Kentucky bluegrass. The answer, however, is that annual bluegrass is classified as a weed by most people in the lawn care industry.

Annual bluegrass is seen as undesirable in residential lawns, which is the main criterion for categorizing a grassy plant as an invasive weed. Annual bluegrass has shallow, weak roots that often steal nutrients and water away from the surrounding turfgrass in a lawn. This weed thrives in poor soil conditions and will even seek out thin patches of grass. Homeowners mostly dislike annual bluegrass because of its unsightly, bright green growth that makes lawns appear uneven and patchy.

What Does Annual Bluegrass Look Like?

What does Bluegrass look like

Annual bluegrass is a small, light green grassy weed that can grow to be 6 to 12 inches tall. The leaves of annual bluegrass are long and thin, with a canoe-shaped tip. The leaf blades are rolled up at the edges, which is a key identifying factor for this weed. The seedheads of annual bluegrass are very fine and delicate, often appearing as if they have been made out of cotton. These seedheads tend to be white or faintly light pink in color, and they will appear on the plant in mid-to-late spring.

Differentiating annual bluegrass from the surrounding turfgrass can be difficult, especially if the lawn is mostly made up of Kentucky bluegrass. However, there are a few key identifying factors that can help you tell these two grasses apart. Annual bluegrass has much narrower leaves than Kentucky bluegrass. The leaf blades of annual bluegrass also have a rolled appearance, while the leaves of Kentucky bluegrass are flat. Finally, annual bluegrass produces small and fine seedheads, while Kentucky bluegrass produces larger seedheads.

The roots of annual bluegrass are also very different from the roots of Kentucky bluegrass. The roots of annual bluegrass are very shallow, while the roots of Kentucky bluegrass can grow up to 6 feet deep. This difference in root systems is one of the reasons why annual bluegrass is seen as a weed. Below are just a few key points to keep in mind when trying to spot annual bluegrass:

  • The grass will appear brighter/lighter in color than surrounding grass.
  • The leaves are smooth and have a canoe-shaped tip.
  • Leaves are spread somewhat far apart.
  • The seedhead is very fine and cotton-like.
  • Growth happens in a bunching pattern.
  • Shallow roots can be seen if you pull the weed.

When & Where Does Annual Bluegrass Grow?

water puddling up on a lawn (2)

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 for the year. Once soil temperatures reach down to 70 degrees or below, annual bluegrass seeds will begin to germinate. From germination, the plant will emerge in fall, go dormant during winter, and finish its life cycle the following spring, when temperatures get warmer.

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 seeds, which can remain viable in the soil for up to 5 years. The distinctive, delicate seedhead 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 seedhead is contacted. This method of expansion is what makes annual bluegrass such a nuisance to homeowners and lawn care experts. 

This weed can also spread through turfgrass sod that has been infested with annual bluegrass. When you install new sod, it is important to make sure that it is free of any weed seeds, including annual bluegrass. If there are any weed seeds present in the sod, they will likely germinate and infest your lawn.

How To Treat Annual Bluegrass

Heart Lawn

As is the case with most lawn care issues, prevention is always better than corrective action. Maintaining a healthy lawn is truly the best way to keep annual bluegrass off your property, but things happen, and weeds will always find a way to grow in lawns. The tips below will help you to both remove and prevent annual bluegrass from taking over your lawn.

  • Hand Removal: This is the most effective way to get rid of small patches of annual bluegrass. To remove the weed by hand, use a garden trowel or shovel to dig up the entire plant, including the roots. Be sure to dispose of the weed properly, either by throwing it in the trash or composting it.
 
  • Pre-Emergent: Pre-emergent herbicides are a great way to prevent annual bluegrass from ever taking hold in your lawn. These products work by creating a barrier in the soil that prevents weed seeds from germinating. Be sure to apply pre-emergent herbicides in late summer or early fall, before annual bluegrass has a chance to germinate.
 
  • Mowing: Mowing your lawn on a regular basis is one of the best ways to prevent annual bluegrass from taking over. This is a short weed in comparison to many grasses, so keeping your lawn a little higher than normal (3 to 4 inches) could help suffocate the shorter weeds.
The importance of mowing your grass to the proper height
  • Fertilizing: Applying fertilizer to your lawn on a regular basis will also help to prevent annual bluegrass. A healthy, thick lawn is much better equipped to crowd out weeds than a thin, patchy lawn. Be sure to apply fertilizer according to the manufacturer’s instructions, as too much fertilizer can actually do more harm than good.
 
  • Reseeding: Reseeding your lawn on a regular basis will help to fill in any thin or patchy areas where annual bluegrass might be able to take hold. Be sure to use quality seed that is suited for your climate and soil type, and lay the seed down in late summer in order to stop the weed before it starts germinating.
 
  • Watering: Proper watering is essential for maintaining a healthy lawn. Be sure to water your lawn deeply and infrequently, as this will encourage deeper root growth. Deep roots are much better at crowding out annual bluegrass than shallow roots.
 

If annual bluegrass has already taken over parts of your lawn, be sure to select a herbicide that is specifically designed to kill annual bluegrass, as other herbicides will not be effective. The longer you wait to act, the bigger your annual bluegrass problem will become. For the best results and the healthiest lawn possible, call your local lawn care provider today!

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