Evergreen Lawn, fact or fiction?

Researcher looking at turf
Photo credit: EESC slide collection
Q:

Is there a grass that stays green year around in the Willamette Valley? I thought perennial rye would but am not sure now.

- Benton County, Oregon
A:

All the cool season turf grasses will stay green year around, but you have to water them in the summer. No grass will stay green if you don't water it. Some can stay green longer than others under short term drought, but in the Willamette, our drought period is long enough that all the cool season grasses will turn brown if you don't water them in the summer. And grasses such as perennial ryegrass and tall fescue do not go dormant, so some of those plants will die and your lawn will "clump out" and other grasses and weeds will move in.

Most lawns in the Willamette Valley have converted to bentgrass naturally over time because it goes dormant and can survive long term drought. It also does not require as much fertilizer as perennial ryegrass, but it needs to be mowed at 3/4" - 1 1/4" to look good (which is lower than what most rotary mowers will cut at), and it needs to be watered regularly or it will turn brown too.

The reality is that even if you plant perennial ryegrass in the Willamette Valley, it will convert to something else. If you water and fertilize it regularly, it will convert to annual bluegrass (the grass that is light green and flowers heavily in the spring). If you don't fertilize it much and don't water it, your lawn will convert to bentgrass. Both of these grasses come from seed present in your soil. And annual bluegrass flowers profusely, so it never lacks for a seed source. The conversion will start in the first year and accelerate rapidly in years 2 and 3. By year 5, you will have a blend of grasses - perennial ryegrass, bentgrass, annual bluegrass, and probably a couple others as well.

Brian McDonald
Senior Turfgrass Research Assistant
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