Save my Lawn or Start Over

Question: My lawn has developed significant amounts of some kind of invader species. It may be that I have a mix of species (different color and growth pattern). At first I thought it was crabgrass but in looking on your website some looks like it could be annual bluegreass (maybe?).  The lawn is thin and I think it needs to be aerated, as I've noticed it doesn't seem to drain very well. I'm guessing there isn't a simple answer, but is it possible to tell from the pictures what I'm dealing with? I am trying to weigh starting over versus investing some time to try to improve health of the existing lawn. I'm worried I've let whatever this alternative species is spread too much, but maybe not. If you do have any insight it is greatly appreciated.

Thank you, 

Matthew Call

responder: Brian McDonald Replied May 02, 2023, 12:33 PM EDT
response: Hello Matthew,  The invading species look to be annual bluegrass and Roughstalk bluegrass. In Oregon, encroachment of other grasses is normal over time. If you want a perfect perennial ryegrass lawn, you will have to spray both post and pre-emergent herbicides every year (5 or more applications per year) and you will still see encroachment over time. The post emergent herbicide needs to be applied by a commercial applicator. In spite of all these efforts, at some point, you will have to kill your lawn with glyphosate, cardboard, or plastic and start over.  Every golf course in western Oregon has converted to entirely annual bluegrass in spite of large budgets to try and prevent it. The good news is that annual bluegrass can make a really nice lawn, albeit a little lighter in color.  My recommendation would be to let it convert and focus on good maintenance. Once the different grasses coalesce, your lawn will not look so splotchy.   As far as coring goes, it will only improve infiltration if you have compaction on the surface because the water needs to infiltrate the surface and then move through the soil and go somewhere (i.e., out a drain). With our clay soils, unless you can get water into subsurface drainage (i.e., through a French drain), the soils only drain so fast, which is pretty slow. On soil, even French drains are moderately effective, and only if you have a slope on your lawn where excess water will move on the surface and get into the drain.  Coring is a really good maintenance practice to help your lawn develop a healthier root system which can reduce water use, but it is only of limited usage to improve drainage on a soil lawn because water moves through soil so slowly.  The easiest thing to do right now is to overseed the bare spots with more perennial ryegrass. But I would check to see if you have crane fly larvae in your soil as they can thin out our lawn. Take a 6" flat shovel and cut a "6 inch square about 3 inches deep. Turn the sod over and sift through the soil with a 3-tined hand weeding tool are some other sharp object. If you have high crane fly larvae populations, you will find them. You should find 6 or more in that size sod piece. Often, they will be near the surface in the top 1", but they can be at different depths. Look on the internet for a photo of European crane fly larvae to see what they look like.  I hope this helps.  Good luck.

responder: The Question Asker Replied May 02, 2023, 12:54 PM EDT
response: That is very helpful. Much appreciated. Thank you.