Annual Bluegrass

Annual Bluegrass (Poa annua)

This is a cool season annual and can be perennial depending on location and strain type. Kentucky Blue Grass (Poa pratensis), Rough Blue Grass (Poa trivialis) and Canada Blue Grass (Poa compressa) are three common turf grasses in the Poa family and found worldwide. Annual Blue Grass is considered a weed and like Bermuda Grass, will die out creating brown and bare patches in lawn.

This annual weed has shallow roots and grows in poorly drained, extremely moist and compacted soils. It can grow in direct sunlight but prefers shade. It also likes cool weather. As temperatures rise it begins to die off.

Poa annua is lighter in color than Kentucky Bluegrass and is often described as having curved 'boat-shaped' leaves about 1/8th inch wide and slightly pointed.

Annual bluegrass stems grow up to 12 inches tall and at the top have an open, feathery panicle, or flower cluster.

Panicles house white seeds
that bloom throughout
growing season.

Weed seeds germinate late summer to late fall and this grass weed starts to grow in spring. Re-seeding happens quickly, during summer into fall. This weed is competitive. It forms dense patches and will take over turf if given the chance.

Use a preemergent herbicide to control annual strains. Apply late summer or early fall (especially if lawn is new) and when evening temperatures begin to cool. Aerate soil to reduce compaction regularly.

When seedlings start to grow in spring pull or hoe immediately. Solarizing black plastic mulch can be an effective manual method of killing weeds. Once under control apply garden mulch.

FYI:

Kentucky Bluegrass, Rough Bluegrass and Canada Blue Grass
(Poa compressa) are popular turf-grasses. If planning on re-seeding lawns, when purchasing grass seed it is important to read bag labels. Sometimes bags will include Poa annua - which isn't good.
When cutting grass it's best to have a grass clippings bag attached to mower. This helps to remove any seed heads.
Fertilizing lawn regularly helps crowd out this common grassy weed.

Related Articles:

Pre-emergent Herbicides

What Preemergent Herbicides are and what they do.

Inorganic Mulch Types

Options other than solarizing black plastic mulch.

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