"Or is it too late to even make a difference this season?"

It is never too late to address weeds :-) And if you wish to have any kind of thick, healthy lawn, you will need to get rid of them. Your removal options are manual or chemical - chemical lawn herbicides are effective and if applied correctly and with care, will have minimal impact on any insects or pollinators. Weed B Gon Plus is effective against more than 200 different common weeds. Do NOT use any weed and feed products - they are highly inefficient and contribute to water pollution.

Overseeding in your area is best left until late summer/early fall - August and September. In the meantime, address the weeds - you may need more than one application of herbicide - consider plug aeration and topdress after with a layer of organic matter as Christopher suggested.

I partially agree with Christopher. I would second the compost idea but fresh cow manure is more of an issue. It stinks, and God gave us noses to keep away from stinky stuff.

And I almost completely agree with Gardengal. When they brought in more soil, is it mounded up or just level with the rest of the yard. Maybe you could post a picture.

Start with a soil test. The Umass one is highly regarded. Then compare to what you need to grow grass. You want a local test, like UMass because they will understand what you have, which is probably acidic. Then get a lawn care book from your library. You want one that is not brand name (ie Scott, selling you on their products). Lastly, why fuss over crabgrass? It's green.

In my yard, I consider grass anything that is green, If I can not grow something green, I mulch it an plant some sort of flowering bush or plant. We have reached the point where we have something in bloom nearly all year.

However since I was raise with a green lawn and now that the trees have grown sufficiently, I am hoping to become more discriminating in what I consider grass

I am absolutely going to send soil samples to UMass. I was going to anyway for some apple trees, and figured lawn would benefit from knowing as well. Thank you for reminding me to get on that!

For some additional information, the septic was absolutely the root of the issue because there's a solid dividing line where they tore up the ground, and where the lawn was left alone. one is plush and soft and grassy. The other... a very motley crew of weeds, some yellow brittle grass, patches of good grass, and random bare bits with nothing growing. I might be misusing the term crabgrass, as I don't really know how to identify the really sharp dry brittle things sticking out that make walking barefoot in the yard unpleasant.

I do not want a perfectly uniform or weedless lawn in the long run. But, I think for grass to play catchup I need to really brutalize some of the weeds this year.

Ortho Weed B Gon seems like a good option to start. I also have a ton of clover and moss, not sure Ortho will work on them, but honestly I'm less concerned with them, as they're at least soft and green. I like that it's more focused so that I can choose which patches to apply to and not just nuke my yard with too many chemicals.

As for aeration and top dressing... I'm sure that'll be partly informed by the soil test. But do I stop dress with compost? Or with new topsoil? Both? Does anyone have any brands they like for that? I don't have any machines for aeration but I do have a pitch fork that might do in a pinch.

Once that's done, I imagine I'll be doing some fertilizing based on whatever nutrients are lacking in the soil test, right?

But, I am NOT supposed to plant new grass seeds until late summer?

Spring is for planting!!!! Plant the grass now. Don't buy grass seed from bags in a big box store. Much of what's in them is weeds. Well they're weeds in your climate. In other climates the seed you need would also be weeds for them. But your not only paying for seed you don't need but you're planting seed that'll haunt you forever. I'm talking Bermuda grass. My neighbor planted about a 1/3 of an acre with the stuff. It's all over the beds, A 3 foot wall of brown grass all winter in the vacant lawn on the other side of me. It's invaded the deep woods in back. And it sends runners all through my gardens.

Find a place that sells grass seed from a large container with a scoop and a scale. Find a mix with perennial rye, fescue and Kentucky Blue grass. Here they sell a mix called Penn State Mix, maybe they sell the same mix as Mass Mix, I don't know. What I've always used is from Pennington Seed. They're getting bashed on the Internet, but I've never had problems with it.

They used to recommend 3 pounds per 1000 Sq Ft. Now they say 4 pounds. I've always applied grass seed thick. Maybe 6 pounds per 1000 Sq Ft.

I'd suggest you cover it with bulk Mushroom Compost which doesn't smell as bad as manure. When it rains on it or you water it most of the smell is gone. On either product. Spread the seed and then the mushroom compost about an inch thick. Throw the shovels full or rock the shovel so it falls off the sides as you rock. The depth isn't a science project. Two inches won't stop the seed from sprouting or keep the old grass from coming up thru it. But 2 inches costs twice as much as an inch.

As far as the crab grass it's too late for this year. It's already sprouted. 2nd or 3rd week of April is about it to keep it from sprouting with pre-emergent. Weed killer won't kill it as it's a grass. As far as watering don't over do it. If it rains don't water. If it rains this evening don't water tomorrow, unless it gets to 90 or so. Remember one of the advantages of the mushroom compost is it keeps moisture in and under it.

After it sprouts you'll see off grass sprouting. It has a different lighter green color. Pull it, it should come out easy. Walking on the grass won't hurt it. Mow it when it needs it. Waiting till you can't get the mower thru it or can't pick up the clippings won't make it worth putting off mowing.

You can use a weed killer a month after the seed germinates. But remember; the fescue and Kentucky Blue grass takes 3 weeks to germinate. So wait at least 6 weeks to apply weed killer.

This fall over seed with the same grass seed or spot seed as needed. Next spring apply the Pre-emergent for the crab grass.

Oh my! I see John D disagrees with the rest of us. Here is why you don't plant grass seed in the spring. Crabgrass is a summer annual plant which drops seed in the late summer and fall so they can germinate in the spring. Germination requires several days of moist soil just like grass seed does. One main difference is that crabgrass can germinate in a very few days while rye grass takes a week, fescue takes 2 weeks, and Kentucky bluegrass takes 3-4 weeks. So if you plant KBG and water it for 3 weeks starting now, you'll have a yard full of crabgrass maturing quickly after it sprouts sometime in May. The second reason you don't want to sow grass seed in the spring is the tender new roots will not have had time to harden off to withstand the dry and warm summer soil. The grass will go dormant quickly which allows the crabgrass to take over completely. Whereas if you sow grass seed in late summer or early fall, the crabgrass will not germinate. That gives the new grass 9 months to mature without competition from crabgrass. Starting in late summer also give you a window to evaluate if you got enough seed down with time to add more before the frost hits. Grass seeded in the fall is much more likely to make it until the following fall. Having said all that, sure if you really want something green now, you can put down some grass seed. I would not spend a lot on it, as I think you'll have better results in the fall if you overseed with a better variety of grass(es).

The soil test will not tell you anything about aeration or whether you need more soil. Chances are very good that you do not need more topsoil. Compost would be something of value for topdressing if you must. It is not necessary, but if you want to spend the money and time, it's an interesting experience. Gardengal and I disagree on aeration, and I don't want to lose track of the topic. I don't aerate and she aerates all the time. We both seem to have our reasons.

Mother Nature does not bury Her grass seed under a mountain of topdressing. Her fields are trampled by animals which knock the seed to the ground and step on it. That's all you need to do. Scatter it and step on it. If you have a large area you can roll it down with a rented water fillable roller.

I discussed the crabgrass problem. If they had crabgrass last year they'll have it this year. That's no reason to not grow grass. The only reason to not grow grass in spring is that it's an urban legend or you're, perhaps, in Texas.

The spring is usually nice and wet here and I'm somewhat sure about Massachusetts. Late summer is very dry here; late August and September. And it gets very hot. Much hotter and dryer than in April.

If a person want's a green lawn now why wait out the seasons. Do it now. The grass will grow. I can almost guarantee it!

As I see it the main problem is a lack of topsoil from reading the OP's post. Grass will grow if you scatter some seed. But spreading grass seed doesn't improve the soil.

Can't say if this would be reasonable for the OP, but what I finally did for my sputtering, compacted soil, full sun lawn (motivated by heavy equipment on it from a fallen tree and porch repair, but I had a problem stretch persisting for years after a water main replacement) was to first kill any weeds (I didn't have a lot), gather a bunch of amendments - shredded paper, leaves, compost etc - then rented a rototiller and tilled it all in. Raked the tilled soil smooth and planted a mix of turf type tall fescues from the local nursery and Gardens Alive. Once the grass had grown enough - late fall - I laid down corn gluten meal to suppress weed seeds from sprouting. In the early spring I patched in any thin or bare spots with more seed. I now have a thick, weed free lawn. I only use corn gluten meal to feed and suppress weeds except when some of the creeping bent grass from next door gets a firm foothold along the edge of the lawn.

In comparison, I didn't till the side yard, and the difference is visible. I have read that soil shouldn't be tilled but in my case it made a huge difference in the growth of the grass.

I should mention that the topsoil layer was pretty thin, with dense clay underlying it.

raee, I don't like rototilling for 2 reasons, but in your case, 3 reasons. Reason 1) over a period of 3 years the fluffy soil will continue to settle unevenly leaving a surface bumpy and getting bumpier. Reason 2) rototilling destroys the soil structure that it takes 3 years to develop. Corollary to this reason is that the soil environment contains microbes that will die if they are dug up and moved to another soil depth/stratum. Reason 3) burying paper or anything woody tends to slow down the decomposition of those materials. The decomposer fungi need a lot of nitrogen to do the job which they normally get from the open air. When they are buried, the nitrogen comes from fertilizers you use on the lawn. Now, having said that, congratulations on the success. Starting in the fall was key to that success. Had you started in late summer you could have done the patching just weeks later instead of waiting until spring. If you would like to improve your side yard, you might open a new topic to discuss it.

John D said, "If they had crabgrass last year they'll have it this year." If that were true then we would all have crabgrass. Planting the right grasses at the right time of year and taking proper care of them can alleviate the crabgrass problem.

He also said, "The only reason to not grow grass in spring is that it's an urban legend or you're, perhaps, in Texas." I think what you meant to say is that the only reason not to sow seed in spring is an urban legend. That statement is a little vague in describing what the urban legend is. In 20 years of dealing with professionals and amateurs in lawn care forums, the consensus is that seeding cool season grass in the spring is a mistake with very few exceptions. The known exceptions are if you live in the Pacific Northwest and sometimes if you live north of South Dakota. Massachusetts might fit in as being north enough to seed in the spring without getting into the troubles I described earlier. When I lived in Dayton spring seeding would have been a big mistake due to the summer heat as John described.

Topsoil and clay can be improved. Just growing stuff will help due to the activity of the roots in the soil. As grass roots are sloughed off, they become food for the microbes living in the soil. Both the roots and the microbes improve the health of the soil. Another way to kick the improvements up a notch is to use organic fertilizer instead of chemical fertilizer.

In this area it is common for builders to get a footer and the concrete block in place before late fall and hopefully get it framed out also. Over the winter they work finishing inside the building. Those homes/buildings can't have the landscaping done over the winter. It's done in the spring. That's when the lawn gets put in. Big homes; million dollar homes. Those people aren't satisfied with a crappy weed filled lawn till fall. They get beautiful lawns done by people who know what they're doing before closing on the house.

The difference between sowing grass in spring or in fall is the amount of water used. The usage in many cases/seasons is less if planted in the spring. Over the summer all nice lawns are watered regularly. There's no shortage of water here.

OP has a septic system which caused this problem. I would bet they also have a well. I would guess that OP's lot is a half acre minimum; probably an acre or more. And it's my guess that the septic tank job involved digging a hole about 5X8' and piling the dirt from about 4 feet deep at most? So the area disturbed was 12' X 12'? There was probably some rutting. This is not a huge project. The good soil OP had is still there buried over top of the septic tank. Get some good grass seed down and cover it with mushroom compost, or peat or corn gluten meal or alfalfa meal. I have experience with peat, straw and mushroom compost. Peat will float away, straw is impossible to get back out of the lawn and looks terrible for a looong time. I recommend planting the grass when you need it. Spring, summer, fall, I've done it in mid December in zone 6 SW Pennsylvania and it sprouted for Christmas. Granted I was lucky. But get the job done so you can enjoy a nice looking lawn.

We had problems with crab grass a few summers ago and since it had already emerged we tried Weed B Gone crab grass killer on the lawn. It worked great, which I was really surprise. Killed it all within a couple of weeks. My brother is a horticulture specialist and he didn't think it would be effective, but it was. Since then we have treated the lawn in early spring with the pre-emergent stuff, and so far no more problems with crab grass.

Dchall, I certainly have no scientific knowledge about turf/soil structure, only experiential. I can only tell you that this is the 3rd year since I renovated that front lawn, and am not seeing any issues with bumpy settling. Further, I used the same method a few years before, when creating large garden beds in over half of my back yard - which would always have standing water after a heavy rain. No more standing water, and the year after I could dig quite deeply into the beds while planting and find no remains of the amendments visible - but lots of worms! The soil is still nice.

I suspect that loosening that very compacted clay soil has enabled the grass to root more deeply, allowing more vigor (and tolerance of dry spells). .

Emily - Thanks for the update, which I obviously needed!