Annual Bluegrass Lawn Weed

Advice from the Help Desk of the
UC Master Gardeners Program of Contra Costa

Client:  This weed is growing in my lawn. Could you please tell me what it is and how do I eradicate and/or prevent it?

MGCC Help Desk:  Thank you for bringing the weed sample from your lawn for identification and recommendations on its elimination and control.

We have been able to identify this sample as Annual Bluegrass (Poa annua), a very common lawn weed in coastal areas of California. This annual weed looks similar to regular lawn grass for a short while. It also looks a little like Kentucky bluegrass, except it has a lighter shade of green, shallower roots, and develops a short seed head early in the season. It dies off when the weather gets hot, leaving big empty patches in your lawn

Annual bluegrass loves damp, shady areas. You can reduce favorable conditions for this weed by watering deeply and infrequently. The weed's shallow roots will not be able to reach down to where the moisture is. Annual Bluegrass will also invade lawns where the soil has become compacted. You can reduce lawn compaction by aerating during non-sprouting periods. This will allow water to settle deeper in the soil away from the shallow-rooted weeds.

Annual Bluegrass typically grows in dense, low clumps, 3 to 12 inches (8–30 cm) tall. To reduce its ability to survive in your lawn, mow your grass high, preferably between 3-4 inches to shade out the weed. Lawns with taller grass tend to have fewer Annual Bluegrass problems. Mowing high will also reduce the opportunity for flowering. Annual bluegrass reproduces by seed and can have many generations in a single season if left to flower and set seed.

For more information on this weed and its control, please see the UC Davis publication, How to Manage Pests in Gardens and Landscapes - Annual Bluegrass at http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7464.html.

Please let us know if you have any additional questions

Help Desk of the UC Master Gardener Program of Contra Costa County (VLT)

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Note: The  UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions.  Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA  94523. We can also be reached via telephone:  (925) 646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog  (//ucanr.edu/blogs/CCMGBlog/). 

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