weed 1

weed 2 -

When was he planning on seeding? If your landscaper want's to do it now, then he is ignorant on the timing of cool season grass and you shouldn't do what he says. The best time to seed in MA is around Sept. 1st, as that is when the heat and humidity breaks, and the nights become cooler. Weeds should be killed prior to seeding, as they will only be a hindrance to your new grass and if you let the weeds go to seed you will have to deal with them next year. You can kill them now with selective herbicides to limit spread and seeding (Weed B Gone products) and then kill everything with Round Up two weeks before seeding. Removing as much dead grass and weeds as you can with a mower set on the lowest setting is a good way to clear the seedbed of the dead plant matter. A lot of people worry about Round Up and weed killers, but the fact of the matter is they have been around for decades, have been studied extensively by many agencies and universities, are usually analogs of natural plant substances, and are not going to find their way into your food unless you are subsistence farmers. These herbicides are degraded by soil bacteria in a relatively short amount of time. Personally I would do a soil test now to determine what your soil is lacking. Putting down organic fertilizers throughout the summer will help raise your soil's organic matter percentage, which would be great for new grass.

What tiemco said. I imagine your pictures are of small areas of your lawn and may not be representative of the majority of the lawn, but what was the reason you dethatched?

Thanks for responding.. to answer your questions.. there are large sections of our lawn covered in those weeds in pic #1.. i thought i uploaded a pic, but it looks like it didn't make it, so i attached it with this post. it's like a field of those weeds.. i'm overwhelmed, since i thought it might be feasible to remove them by hand.. there are also patches of crab grass everywhere. there is a large patch of the tallish weeds in pic #2 as well.
we understood that seeding now isn't ideal, but our landscaper said that since we have a sprinkler system we could water it a lot and it might work better because we then could try to control any issues with run off due to our slope.
as for dethatching - we were told it would help remove weeds and then that it would help increase the soil to seed contact and loosen up the soil. Of course, they dethatched 2 weeks ago and haven't put down loam or seed since, so i'm not sure what the point was now.
as for chemical applications.. i have to say that i want to believe that round up is safe, but even if it is.. the monsanto business practices i've read about just make me want to avoid them. are there other alternatives? i'm not completely against it, i just want to understand if i have other options.
i'm thinking we need to halt this process right now and deal with the weeds. with my luck, we'll get a truck load of loam tomorrow though.
thanks for the responses.. please let me know if you have any other thoughts about our lawn.

Based on your posts, other than improving conditions for weed growth, dethatching was not advisable-especially this time of year. Without passing judgment on your landscaper, dethatching was really bad advice.
Hands down, the best weed preventative (and most enviormentally safe) is a thick healthy lawn. I've never been able to satisfactorily identify the weed in your first picture, but I once had it in my lawn in spades and no turf friendly (WeedBgone) herbicides had any effect. However, now that I have a thick turf, I haven't had one outbreak of any weed. (This years count is 7 broadleaf weeds and one small patch of POA) In the past year the only herbicide I've used is one spot treatment with WBG. Although some people report moderate success using organics as a preventative, I know of no organic weed killer that works. Both WBG and RU work. Sometimes we need to "bite the bullet" to reach our goal. Otherwise we are just screaming at the wind. Once you have a thick healthy lawn, your weed problems will be nil and you wont need to use the products of manufacturers you take issue with.

"as for chemical applications.. i have to say that i want to believe that round up is safe, but even if it is.. the monsanto business practices i've read about just make me want to avoid them. are there other alternatives? i'm not completely against it, i just want to understand if i have other options. "

Round-Up's active ingredient, glyphosate, is not protected by patents anymore, so you can buy any company's weed and grass killer that contains glyphosate and it won't contribute to Monsanto's coffers. I used Ortho's product, available at Home Depot. Glyphosate is safe, just don't drink it.

As for the dethatching, I don't think it was the worst idea, since any weed seeds it stirred up you can kill now with herbicides. Seeding now, even with a sprinkler system, is still not a good idea. If you don't want to kill everything now, then just mow your weeds like a lawn, that will at least give you some green, prevent erosion, and limit their seeding. Don't let your landscaper push you around, he just want's the paycheck, he knows it's the worst time to seed, but really doesn't care. If he doesn't know that, then he is not a very good landscaper.

"As for the dethatching, I don't think it was the worst idea, since any weed seeds it stirred up you can kill now with herbicides."

tiemco, what advantage was there to dethaching the OP's lawn other than padding the landscapper's pocket? I guess you are technically correct as sowing salt would be one worse idea, but I can't think of any advantage in this situation. Are you promoting dethatching for the advantage of growing more weeds so you can kill them?

If there was a heavy thatch layer, it would prevent good seed to soil contact, can harbor lawn pests and fungal spores, interfere with rooting of new grass, affect water infiltration, and doesn't really do much good for your lawn. Did the landscaper show you the thatch layer, or did you see them dethatch? He certainly could have done it just to up the bill, but if it was necessary then I say do it. Removing thatch with a power rake generally doesn't go deep enough to really stir up a ton of weed seeds as you are just skimming the soil, most seeds at that level would germinate anyway especially with all the watering that is necessary for growing new grass. I would worry more about weed seeds from core aeration and that new loam being brought to your yard. Any dorment seeds brought up can be dealt with now anyway, so it's not really an issue.