- Kentucky Bluegrass (KBG) has slightly better heat tolerance but will require lots of water to overcome heat and drought stress of summer to avoid dormancy.
- KBG will have better cold tolerance over the winter in the northern colder areas such as Minnesota, Montana, or the Canadian lawns north of the US.
- Perennial Rye will fare better in mild cold season locations that get regular water from irrigation or rain such as the Pacific Northwest.
- KBG is a Rhizomatic grass type that will spread horizontally on the ground via it’s underground rhizomes. Perennial ryegrass will not spread similarly, it will bunch in small clumps like a tall fescue however the bunches are much less lumpy and can be maintained at a much shorter height.
- PR is a grass that will do well when cut in the 1-2″ range while KBG will do better when cut in the 2-3″range. During periods of high heat and/or drought KBG will perform better if maintained on a higher height of cut in the 3-3.5″range similar to a tall fescue.
- PR will not usually tolerate high heat for long; extended stretches of intense heat will cause it to die off which is why it’s frequently used as a winter lawn cover crop in high heat zones in the lower transition and upper warm season grass zones- places like northern Texas, Georgia, or various locations throughout California and the greater the South West.
- KBG will usually require more fertilization in addition to more water to remain healthy than PR although PR does do well in wetter conditions.
- Both grass types will suffer from disease and fungus if not well fertilized and if irrigation leaves leaf tissues wet too often and for long stretches of time. KBG tends to resist disease a bit better than PR with all things being equal however
- For foot traffic tolerance both grass types will give you similar results although most people find PR will hold up better over the long haul so long as you are ok overseeding thin areas every fall.
- If you apply weed preventors to your lawn every Spring (or fall for Poa Annua) you’ll usually find fewer complications in getting the timing right when growing PR in a lawn over KBG.
- The lowest 1/8″ base of PR will usually be a magenta color and the area where the leaf branches out from the center shoot will have a small auricle “arms” that wrap around the center stalk. KBG will not have a magenta color emerging from the ground and the auricle isn’t really there at all – it will look like nothing is trying to wrap around the center stalk.
- Seed heads that emerge from KBG will look like a miniature pine tree in shape and fullness while seed head from perennial rye will be a tall shoot resembling the tops of wheat. The KBG seed head has a blueish tint which is where KBG gets the “blue” in it’s name.
- Both grass times have a folded vernation meaning as the new leaves emerge from the center stalk they are folded at the base and open up to nearly flat or boat shape at the tips.
- Leaf texture is the easiest way to differentiate these grasses. PR has a matte side of the leaf blade and a shiny side with a mild vein running vertically up and down the leaf. KBG on the other hand has more of a uniform leaf texture that is closer to matte than shiny and the vertical rib on the blade is much more noticeable.
- Generally both grass types look very similar to the untrained eye and they feel very similar too, very soft to the touch which is why they are blended together often in seed and sod. KBG will do better in full sun while PR can tolerate a bit more shade but not much more.
- It is far easier and faster to establish PR from seed than it is to establish KBG. KBG germinates slower (albeit at slightly cooler temps) than PR and will grow slower for the first couple of months but once established it will self repair whenever damage or disease occurs as the rhizomes from healthy turf spread into thin areas. PR will not repair itself and will thus require overseeding to fix blemishes or bare spots.
- Because KBG is rhizomatic it is the cool season grass type that requires dethatching more frequently than any others. PR rarely will need dethatching at all on it’s own but KBG can benefit from light mechanical thatch removal and regular liquid dethatch applications.
Overall both grass types are excellent choices for cool season lawn owners that can get enough water on the ground once or twice a week to keep them green through the summer. For cooler areas that don’t get much water very often then neither grass type will work… tall fescues would be better. And for those people that experience heavy shade from dense trees or buildings then mixing in plenty of fine fescue will be the way to go if not going for a 100% fine fescue lawn.
