Grass ID can be difficult because it relies on fine and detailed features hard to see in photos, but this appears to be Annual Bluegrass, a very common species. It favors areas with compacted soil, so if the lawn hasn't been core-aerated in several years, it may benefit from having that done next autumn just prior to overseeding. Information about the plant's life cycle as well as management tips are included in the page linked above. As a winter annual (germinating in fall, overwintering, and reaching the end of its life cycle in spring), it will die out on its own by summer.

Miri

Thank you for your response. I understand it could be hard to tell exactly what kind of grass it is from the picture.
I did some additional research and got a different answer I would like to run by you. And more importantly, to know if it's not annual bluegrass and turns out to be one of the other options listed below if you could provide guidance on how to treat each one, if treatment varies from what you recommended in your response.

• Growth Habit: Annual bluegrass typically stays fairly low, and even a healthy patch of it doesn’t form the large, upright “tufts” you see in the images. Instead, it’s known for producing many small, pale-green clumps that go to seed at very low mowing heights.
• Color & Texture: Annual bluegrass tends to be a lighter or “apple” green, whereas the clumps you have are a deeper green and coarser in texture.
• Seed Heads: One of the telltale signs of annual bluegrass is its seed heads, which can appear even at just an inch or two tall in spring. If you haven’t seen fine, white-to-pale-green seed heads at low mowing heights, it’s probably not annual bluegrass.

Based on the photos, the coarse texture and upright, clumpy growth point more toward a pasture-type tall fescue (e.g., K-31) or possibly orchardgrass rather than annual bluegrass.

We can share a couple grass ID resources linked below that will be more definitive, since soil nutrient and pH levels can influence how deep or yellow-green a grass' foliage can be, and height and growth habit also can vary with soil compaction and (later in the season) mowing height. Grass ID traits rely on structural features like ligules, vernation type, collar shape, and other aspects that typically require magnification or close inspection to see clearly. (Explanations and illustrations of those terms are included in the linked resources below.) Lawns tend to be comprised of more than one grass species (often tall fescue dominant with a bit of fine fescue, perennial ryegrass, and/or Kentucky bluegrass mixed in, so try to sample only grass blades in the mystery clumps for identification).

• Turfgrass ID key -- Ohio State University
• Cool-season Turfgrass Identification -- Penn State

The grass pictured appears to have "boat-shaped" (or keeled) leaf tips, a characteristic trait of Poa (bluegrass) species. This would narrow it down to either Annual Bluegrass or Roughstalk Bluegrass, though it doesn't appear to have the growth habit of the latter. If/when it goes to seed, Annual Bluegrass will rapidly re-form seed heads if they are cut off by the mower (though it can also produce seed heads lower than mowing height), whereas that won't happen as prominently as with Roughstalk Bluegrass. As an annual, Annual Bluegrass dies back fairly rapidly at the end of spring, and is gone by summer. Roughstalk Bluegrass also looks like it's dying by late spring and early summer, since it goes dormant in hot weather, but as a perennial, it regrows once the weather cools again.

'Kentucky 31' is much coarser than the pictured grass, and Orchardgrass also has some features different from Poa grasses.

In Montgomery County, nearly all areas are prohibited from using non-organic herbicides on lawn weeds. For annual weeds, management will be easier since the plants will die out on their own (winter annuals die by the coming summer, and summer annuals die by the coming winter), and you can focus on overseeding (in late summer or early autumn) instead to thicken-up the lawn with desirable cultivars of grass.

For perennial weeds, management will be more difficult, and requires either digging out weed clumps or repeatedly treating them with one of the approved herbicides. Since those are contact-only, not systemic (root-killing), they work by exhausting the plant, forcing it to keep regrowing after every application that kills above-ground growth, which eventually uses-up the root energy stores and kills the plant. How long that process takes is hard to predict, but it might be several weeks at least, depending on when the weed in question is in active growth versus entering dormancy.

Miri