Kentucky bluegrass is itself a division of a larger family of bluegrass that includes rough bluegrass, a shade-tolerant grass; Canadian bluegrass, a cold-tolerant cousin; and annual bluegrass, a nuisance weed. Versatile Kentucky bluegrass, however, has hundreds of varieties that fall into three categories. Of these, the grasses in Category 1, classified as "Elite Turf Types" by Rutgers Cook College, are most often chosen for their vigor and resistance to turf diseases.
Compact types grow low and dense; they tolerate mowing heights as short as 1/2 inch and provide high-quality turf. Compact varieties may have a purple winter color, a long winter dormancy period and are very resistant to leaf spot disease. Compact Midnight varieties may be susceptible to stem and leaf rust and summer patch but have a dark green color and good heat tolerance. Compact America varieties are more drought-resistant, grow well in shade and are resistant to high summer patch and powdery mildew.
Aggressive High-Density and Mid-Atlantic Types
These grasses grow from medium to high density and overcome damage and disease well. Aggressive high-density varieties may become invasive and are very wear-tolerant. Mid-Atlantic varieties are more refined but have deep, strong root systems and spread by extensive rhizome systems; rhizomes are “runners” that grow underground and establish new plants. They are quick to green up in spring.
Julia-type Kentucky bluegrasses are extremely wear-tolerant, superior summer performers. Ulysses, Rampart and Avalanche are Julia varieties that are more resistant to brown patch and dollar spot than other Julia varieties. Julia varieties resist leaf spot and stripe smut.
The CELA type is named for four varieties: Challenger, Eclipse, Liberty and Adelphia. (Seed Research of Oregon adds the Jefferson and Rambo varieties to this group.) They green-up more quickly than compact types, making them good choices for athletic fields. They have good resistance to stripe smut and leaf spot.
Bellevue, Shamrock and Cheri Types
These types are medium growers and good quality home lawn turf grasses. All but Cheri types are susceptible to billbug infestation. Bellevue types tend to have long, tough stems in spring but leaf out as the season progresses; they stay green well into winter and green-up early. Shamrock types spread by strong rhizomes and are heavy seed-producers. Cheri types also are good seed producers and make medium to low-density turf.
According to Rutgers research, BVMG types are a category of varieties that are highly susceptible to stripe smut disease and slow to recover from yellow ring. Seed Research of Oregon lists them as poor winter turf and medium turf performers in summer with stemmy plants, high seed yields and susceptibility to billbugs.
Varieties like Kenblue are often included in lawn mixtures. These varieties constitute a classification of their own. They are vigorous upright growers used for soil stabilization and they produce seed early. Although they withstand heat stress well, they may go dormant during the hottest part of summer.