After working on your lawn this last month, you may be wondering why your lawn has so many different types of grass. I will try to explain as best as I can so that you will have a better idea of which direction to go when budgeting your valuable time and money on your future landscaping projects.

Most of the foreign grasses that invade your lawn do so because there is a breakdown for some reason, usually lack of maintenance. In the spring, all of the local un-mowed fields, meadows and roadsides that have tall un mowed grass will go to seed. The wind picks up the seed as do cars, trucks or anything else that the seed can lodge into and then they eventually end up in your lawn.

When your lawn has a dead area, possibly due to many factors, the seeds settle into the bare spot and germinate. Most healthy lawns will keep the majority of these weed seeds out if properly maintained because the seed needs both light (photosynthesis) and water to germinate. However, even the best manicured lawn will have unwanted grass eventually. I figure the life of the best maintained lawn is no more than 10 years unless it is over seeded annually.

Because grasses are all in the same genus you cannot spray out to differentiate from one grass or another. There is not a selective herbicide that will do this. Roundup, which is a non-selective herbicide, can kill the affected area and after 7 days be re-seeded with the desired grass, usually Perennial Rye.

There are a few main types of grass that will invade your lawn if you do not spend the time maintaining your green space. Here are a few. Call me and I will come over and show you the difference.

• Perennial Rye- This is the desired grass and is used predominately by sod farms in our area. It is a deep, rich green color with fine blades, and when you dig into the root crown it will show red as the root crown enters the soil. It is forever a perennial. Maintained properly, just like a Rhododendron, it will not spread because it is a bunch grass.

• Turf type Tall Fescue- Newly improved, this grass is used in some applications for lawns, although in my opinion, falls short of the quality of Perennial Rye. It is a dark green, thicker leafed Perennial bunch grass. It is more drought tolerant than the rye but is suspect to weed seeds because it is more of an open growing grass in the lawn. Sod farmers are starting to grow this grass and time will tell if it becomes popular.

• Fine Fescue – Sometimes called Chewing’s Fescue, or Red Fescue, it includes all different types of fine bladed Fescues. These grasses do better in shaded conditions and can be mixed in with rye grass to fill in under trees with lots of shade, especially Chewing’s Fescue. Susceptible to wear patterns, it thins when exposed to full sun and has a tendency to create thatch in poor soil areas like the soil most likely in your yard. I have experimented with this variety without much luck. It is a very high maintenance grass.

• Poa Annua- This grass is an annual blue grass that is labeled by Oregon State Extension as a noxious weed. You can identify this grass by its yellowish green color and low growth habit. It is an annoying grass usually taking over in hard, compacted areas of the lawn. Over the next few months this grass will go to seed, propagate and spread with white seeds growing below your lawn mower height. It grows great in the poorly maintained areas of the lawn. Poa Annua plays havoc on golf greens because it will grow below the desired Bent grass on the golf green and below the reel mower height of 3/32nds of an inch. It is impossible to eliminate once it germinates in your lawn. If this happens, spray out with Roundup and over seed with Perennial Rye.

• Poa Trivialis- This is also an annual that spreads by rhizomes and rarely goes to seed. It is hard to spot and will blend in with Rye until it spreads throughout the entire lawn and then must be killed out with roundup.

• Annual Rye-In most lawns this grass turns into a bi-annual and sometimes lives multiple seasons. It blows in with the wind during spring and summer seeding months. It is sometimes confused with Poa Trivialis.

• Tall Fescue- In most cases, this perennial is not a favored grass and blows in during the spring and summer seed months. It has a very wide blade, the widest in your lawn. It is course and dark green, very thick with a heavy crown. It will not spread because it is a bunch grass, but it is definitely an eye sore in the lawn. Dig it out by hand or spray out with roundup and re-seed with Perennial Rye.

• Bent grass- Sometimes called creeping Bent; it is predominately a coast grass that adapts well in dryer climates. There are many different varieties and you can identify it by the round, matted growing patches in your lawn. It will eventually spread throughout the entire lawn. Spray out infected areas with Roundup and re-seed.

• Velvet Grass- I have seen this grass take off lately. It is a perennial and spreads by rhizomes and by seed. Identify this grass by its light green color and fuzzy wide blade. Unlike the other grasses, this grass will spray out using 2-4D, yet is hard to entirely eradicate because the 2-4D is a contact herbicide and usually won’t completely kill the rhizome root system. We usually just kill the infected area with roundup and start over.

• Orchard Grass- This perennial bunch grass is very dark green with a wide stiff blade and looks a lot like Tall fescue. It usually has a broader leaf and crown. Eradicate by pulling, digging out of ground or spray out with Roundup.

• Crab Grass- I don’t see as much of this as the others above because it is more of a warm season grass, thus it would be a summer annual here in the Willamette Valley. Again, there is not much you can do but dig it out and over seed the affected areas.

In review, the list of possible desired grasses for your lawn would be Perennial Rye, Turf Type Tall Fescue, or Chewing’s Fescue. Thee rest are mostly noxious weeds and should be prevented and eradicated from the lawn.

Remember that the best way to control all of these grasses is to properly maintain your lawn. A healthy balance of water, food, aeration and soil PH balance will enable the desired lawn, most likely Perennial Rye, to maintain deep roots. Deep roots means the grass will be thicker up top, thus eliminating most of the unwanted grasses in your lawn.


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