Question
Hi,
I just moved into my first house in Medford MA (near Boston) and am trying to improve our lawn for next year before winter sets in.  We were really busy and so tried to see what would happen with just planting some grass earlier this spring - without much soil preparation.

It didn't turn out half bad - we got somewhat of a lawn I'd say with not too much effort - so I don't think our soil is too bad.  The grass got a bit brown during the summer but this improved significantly after I started watering thoroughly on a weekly basis.

So my grass is green now but I think we've made other mistakes.  First I don't think we put enough seed down.  Our lawn is very thin - i.e. there isn't enough grass to make it a nice lawn you'd want to sit on. There aren't bare spots - rather it is uniformly thin throughout.  What is the best way to make it thicker?  I tried putting down more seed earlier but I don't think it helped.  After doing more research I believe the seed may not be contacting the soil sufficiently.

I beleive the problem is linked to a fatal mistake we made early in the summer - we let the grass grow long (thought it would keep the weeds at bay) and then we didn't collect the clippings.  The clippings became brown and covered the soil where we didn't have grass growing.  Should I de-thatch the lawn, which I believe means to rake up the dried clippings? And then plant more grass seed?  Does this damage the existing grass?

The last problem is weeds.  When is the best time and best stuff to get rid of these?  Interestingly we only have weeds in the part of our yard that gets a lot of sun.

Our lawn could be at a higher level in that when it rains heavily all of the rain in the neighborhood seems to collect in our backyard.  
So I wouldn't mind making an investment in top soil if I knew that would help my thinness and weed problems.

Thank you for your help, I am very motivated to get this lawn thing right.

Answer
You can spread grass seeds in early fall (in a week or so) and walk on the lawn, use a roller or otherwise to ensure good soil seed contact. The best result you have if you use a rake with sharp discs (thatch rake) to scarify the soil and make places for the seeds to lodge. This will damage the existing grass somewhat but done carefully it should not be too bad. thatch rakes costs $20 at home depot. it is a long handle with 5-6 half moon shaped discs with sharp edges which you pull over the soil. You can also rent mechanical dethatchers (vericutters.. the ones with the discs which slices, not the ones with metal arms which pulls thatch up. They would be too destructive).

You do not need to dethatch as such (thatc is partially decomposed roots, crowns and rhizomes which form a barrier between the roots and the green grass. The thatch layer is spongy and although brown like soil, it is felt like in quality and create a thick "cloth like" barrier which water can not penetrate). Dethatching a new lawn is not necerssary. You can use a dethatcher (provided it is the type with the discs) to rip up the soil level for new seeds to lodge into, but not for the purpose of pulling up thatch. Therefore, if you use a mechanical machine then make sure it is set to a very shallow setting (not too deep).

Once seeded, walk on the lawn, or use a landscapers roller to roll the seeds so to ensure good soil/seed contact.

Keep seedbed (lawn area) moist until new seeds germinate. Do this by watering daily (or twice daily) until new seeds are 2-3" tall (will take 2-3 weeks).

You can spread fertilizer w/broadleaf weed control products (weed-and-feed) in late fall (end october) but make sure your new grass (sowed early september) has come up and have been mowed a few times.

Correcting drainage problems is something that I recommend. If the water sits for more than an hour or so, it pays to correct drainage. Just adding soil will probably not be enough, however. You may be looking at installing a drainage pipe which vents off your property.