Annual Bluegrass

There’s the toe tappin’, git yer yee-haw on sort of bluegrass, and then there’s one of the most common landscape weeds: annual bluegrass.
Annual bluegrass (Poa annua) is a cool season annual or biennial that appears that appears  each year with the first rains. This weed is a member of the grass family.

Annual bluegrass (Rasbak) CC BY-SA 3.0

Annual bluegrass identification

Annual bluegrass starts out looking like many lawn grass varieties, Kentucky bluegrass, in particular, except that it has shallower roots, seeds more rapidly, and it is a lighter shade of green. To the untrained eye, grasses are grasses. A yellowish to dark green blade emerges, a couple more blades show up, and then a flowering stalk comes out of the center, hosting a flower cluster that spreads this problem far and wide. To identify annual bluegrass, you will need to take a closer look at the blade. The tip is said to look like the bow of a boat. The mid-blade may have a crinkly section. And the collar, where the blade meets the sheath (or stem), has a slightly pointed, jagged tip. Annual bluegrass grows low to the ground, spreading in clumps that can be 3 to 12 inches tall. The root system is fibrous and you may even see roots emerging from the lower portion of the aboveground stem. Flowers may be seen December through July. Flower heads are egg-shaped or triangular, and can be bright green or purplish.

​Why do you care?

At first glance, this weed may look like an acceptable addition to your lawn. It’s a grass. It’s green. It grows like crazy. So, why would we consider this particular grass a weed? Well, first, it turns brown and dies back as soon as the top of the soil gets dry, leaving ugly, dead patches in your lawn. Those patches then erode or create homes for other weeds. In the garden, this weed robs your edibles of water and nutrients needed to stay healthy and produce an abundant harvest.
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Annual bluegrass control

Watering your lawn deeply and infrequently will make life more difficult for annual bluegrass. It will also make your lawn healthier and more drought tolerant. Also, maintaining your lawn at a height of 3 or 4 inches will shade out this weed. Individual clumps can be dug out as soon as they are seen. I feed them to my chickens, but you can add them to the compost pile, as long as they haven’t gone to seed. Heavy infestations can be treated with pre-emergence herbicides in late summer or early fall, if you use that sort of thing. [I don’t.]

If annual bluegrass is seen in the garden, pull it out before it has a chance to go to seed and spread. You can also lay 6 to 8 sheets of wet newspaper over unplanted areas of the garden and then cover the paper with 2 to 3 inches of organic mulch, such as pine needles, straw, or aged compost. The wet newspaper acts like a weed barrier and the mulch feeds the soil while interfering with weed seed development.