BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Poa pratensis | Kentucky Bluegrass 



GENERAL BOTANICAL CHARACTERISTICS : 
Kentucky bluegrass is an introduced, perennial, short to medium-tall,
cool-season, sod-forming grass.  The leaves are primarily basally
attached and are usually 4 to 12 inches (10-30 cm) long [100].  Stems
are numerous in a tuft and grow 12 to 36 inches (30-91 cm) high.  The
inflorescence is an open panicle.  Kentucky bluegrass is shallow rooted
and is intolerant of drought.  Most roots and rhizomes are found within
3 inches (7.5 cm) of the soil surface [40].


RAUNKIAER LIFE FORM : 
   Geophyte


REGENERATION PROCESSES : 
Kentucky bluegrass is a vigorous herbaceous competitor.  Not only does
it spread by rhizome expansion, it also produces abundant seed which
accounts for good seedling recruitment and establishment on disturbed
sites. 

There are 2.1 to 2.2 million seeds per pound (4.6-4.8 million/kg).
Germinative capacity varies from 75 to 94 percent.  Seeds require light
for germination [35].

In eastern Washington, fresh seed sown in July began germinating on
November 18; seedling emergence continued into December beneath an
occasional snow cover.  Autumn seed germination was regulated more by
temperature and moisture than by the amount or quality of light [14].


SITE CHARACTERISTICS : 
Kentucky bluegrass is widely distributed across North America, growing
on a wide variety of sites in numerous vegetation types, but grows best
and is most abundant on moist sites where the climate is cool and humid.
In tallgrass prairie it may be abundant on uplands and lowlands because
of abundant annual precipitation, but in mixed-grass prairie it is
abundant only on lowland sites [49,105].  In the West, cool, moist
conditions optimal for growth typically occur on northern exposures, at
moderate to high elevations, and in riparian environments [49].  In the
Southwest and in California Kentucky bluegrass is often confined to cool
mountainous regions [113].  It grows best in full sunlight but will
tolerate light shading if moisture and nutrients are favorable [49,100].
Kentucky bluegrass grows in prairies and fields, mountain grasslands,
mountain brushlands, mountain meadows, riparian woodlands, and open
forests and woods.  It is common along roadsides.

Soils:  Kentucky bluegrass grows on a wide variety of soils, but thrives
on well-drained loams or clay loams rich in humus [113].  It also
thrives on soils derived from limestone [49,100,113].  It is somewhat
exacting in its chemical fertility requirements, needing large amounts of
nitrogen during active growth stages [100].  Optimal soil pH is between
5.8 and 8.2 [100].  

Elevation:  Elevational ranges for selected western states are as
follows [27,101,124]:

       State                 Elevational Range

        CO              4,000 to 12,000 feet (1,220-3,659 m)
        MT              2,800 to 7,500 feet (854-2,287 m)
        NM              5,576 to 11,480 feet (1,700-3,500 m)
        UT              4,200 to 10,800 feet (1,280-3,290 m)
        WY              4,600 to 9,100 feet (1,400-2,775 m)

Associated species:  Kentucky bluegrass is ubiquitous.  Associated
species in specific habitats are presented below:

Mountain and riparian meadows: redtop (Agrostis alba), smallwing sedge
(Carex microptera), analogue sedge (C. simulata), timothy (Phleum
pratense), Baltic rush (Juncus balticus), meadow barley (Hordeum
brachyantherum), western aster (Aster occidentalis), common yarrow
(Achillea millefolium), strawberry (Frageria virginiana), largeleaf
avens (Geum macrophyllum), wild iris (Iris missouriensis), cinquefoil
(Potentila gracilis), common dandelion (Taraxacum officinale), velvet
lupine (Lupinus leucophyllus), and buttercup (Ranunculus spp.)
[47,61,68,128].

Mountain grasslands: Big sagebrush (Artemisia tridentata), rough fescue
(Festuca scabrella), Idaho fescue (F. idahoensis), cheatgrass (Bromus
tectorum), mountain brome (B. marginatus), common dandelion, snowberry
(Symphoricarpos albus), and rose (Rosa acicularis) [25,89,95].  


SUCCESSIONAL STATUS : 
Facultative Seral Species

Kentucky bluegrass is extremely competitive.  Due to past grazing and
lowering of water tables in western riparian habitats, Kentucky
bluegrass now dominates many sites once occupied by tufted hairgrass,
woolly sedge (Carex lanuginosa), widefruit sedge (C. eurycarpa), aquatic
sedge (C. aquatilis), bluejoint reedgrass (Calamagrostis canadensis),
Cusick bluegrass, and willows [47,62,88].  Once it has gained dominance,
it is persistent and remains a relatively stable community component.

In the Intermountain West, aspen/Kentucky bluegrass communities are
grazing-induced seral stages which have replaced the following climax or
near climax communities [80,82]:  aspen/mountain snowberry/Fendler
meadowrue (Thalictrum fendleri), aspen/mountain snowberry/pinegrass
(Calamagrostis rubescens), aspen/Fendler meadowrue, aspen/pinegrass,
aspen/mountain snowberry/elk sedge (Carex geyeri), and aspen/elk sedge.

In ponderosa pine and bunchgrass habitat types, Kentucky bluegrass is
often the herbaceous layer dominant on sites with a history of past
grazing abuse.  Daubenmire [25] called such sites a "zootic climax"
because even after the grazing disturbance has been stopped for many
years, there is no indication that Kentucky bluegrass will give way to
the native climax species.  


SEASONAL DEVELOPMENT : 
Kentucky bluegrass is one of the first grasses to resume growth in late
winter or early spring.  It grows rapidly, and in many states it flowers
in May [19,27].  In Kentucky and Missouri, seeds are mature by mid-June
[125].  By midsummer plants become nearly dormant.  With cool
temperatures and precipitation, growth resumes in the fall and continues
until daytime temperatures approach freezing [97,105].

Flowering time for several states is as follows:

Montana - late May and early June [97]
North Dakota - late May and early June [69]
Nebraska - May [105]

Kentucky bluegrass phenology was studied over a 3-year period on the
Sheyenne National Grasslands in southeastern North Dakota.  Timing of
phenological events was as follows (average dates for the 3 years
studied) [69]:

Resumption of spring growth - green leaves observed during snowmelt in
mid-March, but rapid growth began in early April.

Flowering - flower stalks appeared in mid-May.  Most flowering occurred
in late May and early June.  Nearly all plants completed anthesis within
one week.

Seed maturation - mature seeds were observed in mid- to late June.  Seed
stalks became dried after anthesis and were easily removed by wind.
Most stalks were removed by midsummer.  

Senescence and regrowth - maximum leaf height occurred in mid-June and
leaf senescence occurred shortly thereafter.  Plants were semidormant
during midsummer.  Large amounts of vegetative regrowth began in late
July and early August.  Forty percent of leaves present at the end of
August were new growth, which continued for a short time after the first
hard frost.

Related categories for Species: Poa pratensis | Kentucky Bluegrass