Kentucky Bluegrass (Poa pratensis) — Plant Profile

Phenological Calendar

Stage	Typical Window	What to Look For
Spring green-up BBCH 09	Mar 1-Mar 30	Later to green up than ryegrass or fescues; needs warmer soil temps (50°F+)
Active vegetative growth BBCH 21	Apr 1-May 15	Vigorous rhizome spread; fills bare areas
Peak spring growth BBCH 39	May 1-Jun 15	Rapid top growth; seedhead production visible if unmowed
Summer stress / semi-dormancy BBCH 45	Jul 1-Aug 31	Goes semi-dormant in summer heat; browns without consistent irrigation. More heat-sensitive than other cool-season species in western WA.
Fall recovery BBCH 21	Sep 1-Oct 31	Strong fall recovery with cooling temps and rain; good rhizome extension
Winter dormancy BBCH 97	Nov 15-Mar 1	Retains better winter color than some species; rhizomes dormant

Diseases (6)

Thekopsora minima and Naohidemyces vaccinii Rust

Podosphaera aphanis var. aphanis Powdery Mildew

Necrotic Ring Spot

Stripe Smut

Various fungi (Phyllosticta spp., Septoria spp., Cercospo... Leaf Spot

Typhula Snow Mold

Pests (3)

European Crane Fly

White Grub

Billbug

Cultivars (1)

'General modern cultivars'

Modern KBG cultivars offer improved disease resistance, especially to leaf spot and rust, compared to older cultivars. Thousands of cultivars exist. In western WA, select cultivars rated highly for rust resistance and leaf spot resistance by NTEP.