Kentucky Bluegrass - America's Favorite Cool Season Grass

Kentucky bluegrass is by far the favorite and most widely used of all the bluegrass species.

It is one of the more beautiful cool season lawn grasses. It is known for its excellent uniformity, color, density and texture. It can be purchased in both seed or sod. Kentucky bluegrass seed is commonly included in seed mixtures with other fine bladed grass types.

One of the identifying characteristics of bluegrass is its boat shaped tip. If you look carefully, the tip of the blade folds together to resemble the bow of a boat. If you pull the length of the grass through your fingers, the tip will split, leaving two small points. Only orchardgrass has a similar shaped tip.

Bluegrass’ advantages

Kentucky Bluegrass forms a dense and attractive turf. For some people, the thin blades are more appealing than wider bladed grasses.

One of the principle advantages of bluegrass over other cool season grasses is its ability to spread. The fact that it can spread and heal itself when damaged is probably the greatest reason for its popularity. It spreads through the production of rhizomes. See Plant Structure for a complete explanation of rhizomes. Rhizomes are stems that grow horizontally just below the surface of the ground. Each rhizome produces a “node” every few inches along its length from which a new bluegrass plant will sprout. On high traffic lawns where damage is a frequent occurance, bluegrass is an excellent choice. Athletic fields will often use a combination of bluegrass and perennial ryegrass. The bluegrass will heal damages and perennial ryegrass for its high wear resistance.

Kentucky bluegrass seed is blended with tall fescue seed when grown for sod production. Fescue doesn't have the structure to hold sod together, but bluegrass does. When sod is harvested, the roots are cut, but the rhizomes from the bluegrass keep the sod from falling apart.

Since the rhizomes grow underground, they help ensure the survival of the plant. It can survive damage that would kill other grasses. Even if the grass were to be removed at ground level, bluegrass could still grow back because of the underground growing points on the rhizomes.

Kentucky bluegrass has better cold tolerance than other cool season grasses. It can withstand periods of very cold weather that would normally damage fescue or ryegrass. The adaptation zone for bluegrass extends through the cool/humid and cool/arid regions.

However, bluegrass doesn't do well in the south. It is too hot. I have heard from people as far south as Dallas, TX asking how to keep their bluegrass alive. It is always best to choose a grass that does well where you live.

Bluegrass’ disadvantages

Bluegrass is considered a high water user in summer, partly because its root system does not extend as deep into the soil as other grasses. Without proper irrigation or sufficient rainfall in summer, bluegrass is one of the first grasses to go dormant. On the up side, even after extended drought, bluegrass has the remarkable ability to recover from dormancy without damage.

Another disadvantage is that Kentucky Bluegrass is not very shade tolerant and will thin or die if planted in heavy shade. Rough bluegrass, on the other hand, is a variety of bluegrass that has much better shade tolerance. Shade grasses, such as fine fescues, are also compatible with Kentucky bluegrass.

Common and improved bluegrass varieties

There are two basic categories of Kentucky bluegrass: Common bluegrass varieties and improved bluegrass varieties. To see the specific varieties, click on the Cultivars page.

Common bluegrass varieties are the oldest cultivars of Kentucky bluegrass. The older varieties are used in most seed mixtures and is the type usually seen growing in home lawns. The term used for these older varieties have become known as the “public varieties”. It is a very attractive lawn grass with all the attributes listed above. However, the major drawback is that the older cultivars are highly susceptibility to the fungal grass disease called “leaf spot”.

Common bluegrass varieties are best used on sites that will not be receiving regular fertilization and irrigation. This is because common bluegrass will become too disease prone when placed on a fertility program.

This presents a problem with seed mixtures sold in lawn and garden stores. Many of these stores that offer bluegrass, sell the older “public variety". Again, it is not a problem unless you intend to fertilize regularly throughout the season. It is better, if possible, to purchase your seed through a store or warehouse that supplies the landscape and turf industry. Many of these warehouses sell to the public and their employees have a better product knowledge. You can usually get improved Kentucky bluegrass blends that are resistant to leaf spot. Remember, even if bluegrass is a small percentage of the seed mixture, it will reproduce and spread. Most other cool season grasses can not spread like bluegrass.

Improved varieties

Improved varieties were released many years after common bluegrass varieties hit the market. These cultivars have been developed for use on sites that will receive regular fertilization and maintenance. Improved bluegrass was designed to be much more resistant to various turf grass diseases and also have a slower growth rate. If your plan includes regular fertilization and irrigation, the improved varieties are the better choice. These varieties are the types most often used on golf courses and professional recreation areas where fertilization is performed.

Bluegrass maintenance

Irrigation and drought tolerance

Bluegrass has the natural ability to survive several weeks or even months of drought that would injure many other cool season grasses. Following a drought, new growth will spring up from the rhizomes. Bluegrass has a shallow root system, so if it doesn’t rain, it will need to be watered a couple times a week during the summer to keep it green. Kentucky bluegrass should receive at least ½ inch with each watering.

Mowing requirement

Kentucky bluegrass can be mowed as low as 1.5 inches in the cooler times of the year. This height increases to 3 to 4 inches in summer to help it survive the summer heat. Personally, I rarely adjust my mower below 4 inches all year. That may seem high if you are not used to it, but the grass quickly adjusts. The additional blade length enables the grass to endure drought, traffic and other conditions much easier.

Fertilization

In the industry, the amount of fertilizer is stated in pounds of Nitrogen per 1000 sq. ft. per year. Kentucky bluegrass requires 4-5 lbs of nitrogen per 1000 sq. ft per year. There is an easy formula for determining how much fertilizer to apply regardless of the percent of nitrogen in the bag. For full information on lawn fertilizers and how to apply them, see the fertilization section of this site.

Insect problems

Bluegrass can suffer damage from white grubs, billbugs, sod webworms, and leafhoppers. White grub controls can be applied as a preventative. You can use products like Merit by Bayer, Grub-Ex by Scotts or similar products. With these products, they only kill the insects that feed on the grass and not beneficial insects. Insecticides can also be applied as soon as damage is seen. Damage can occur quickly, so it is important to monitor for insects or be aware of the time when they are active.

Disease problems

“Leaf spot” and “melting out” are two of the more common diseases that affect the common bluegrass varieties. They can best be controlled by proper watering techniques and infrequent use of high nitrogen fertilizers. Common bluegrass will become disease prone when fertilized on the same schedule as other grasses.

Necrotic ring spot is another serious disease of heavily fertilized bluegrass. Once established, it is difficult to control. Fungicide treatments are necessary. Preventative maintenance includes core aeration to relieve soil compaction and to help control thatch. As with all grasses, knowledge on the use of organics to build up beneficial micro-organisms is extremely helpful. Beneficial micro-organisms are the natural enemies of disease pathogens.

Other bluegrass varieties

Rough Bluegrass

Rough bluegrass is used in shaded and damp areas. It does not perform well in full sun or in arid dry locations. The exception is when is it used in winter to overseed dormant burmudagrass. This is about the only time when rough bluegrass can make a beautiful, full sun lawn.

Annual bluegrass

Annual bluegrass is grassy weed with a one year life cycle. It is a “winter annual”. Annual bluegrass germinates and matures in the fall, lives through the winter and produces seed in the spring before it dies. It is most noticeable in early spring when other grasses haven’t yet come out of dormancy.

It presents the biggest problem in closely mowed turf where more sunlight is available. Lawns that are mowed at 3 or 4 inches rarely have any problems with annual bluegrass. It can easily thrive in a variety of soil conditions including compacted soil. By the time warm season grasses green up, annual bluegrass has started dying back.

In areas like gravel driveways, Round-Up can be sprayed to control it and other weeds. In lawns, try to manage your grass is such a way that encourages the lawn grass and not the annual bluegrass. The easiest way is to raise the mower blade to mow at higher levels. It doesn't prefer sites where there is too much competition, so maintaining a thick turf is helpful. To control annual bluegrass in warm season grasses, you can try overseeding in the fall with ryegrass. A pre-emergent applied in the fall before annual bluegrass germinates will help. However, only use a pre-emergent if you don’t intend to overseed.