Bog bluegrass is a graminoid, 2-7dm tall, with culms that are slender, solitary or in small tufts. It has a loose and open panicle, mostly 5-10cm long, the branches are long and slender, distant, the lower are mostly in twos, spikelet-bearing above the middle. Spikelets mostly 4-5mm long, narrow, 2-5-flowered. Lemmas are 2.5-3.5mm long, webbed at base with a few long hairs, the keel and lateral nerves are pubescent on the lower half or two-thirds, the intermediate nerves are glabrous and obscure. Sheaths are minutely scabrous. Ligule is short, truncate, the uppermost as much as 1.5mm long. Blades are rather lax, mostly erect, 0.3-2mm wide.
Can be distinguished from other Poa species by its lemmas, which are pubescent on the margins but glabrous between the inconspicuous veins.