Here are the basics of lawn care...

2. Water deeply and infrequently. Deeply means at least an hour in every zone, all at once. Infrequently means monthly during the cool months and no more than weekly during the hottest part of summer. If your grass looks dry before the month/week is up, water longer next time. Deep watering grows deep, drought resistant roots. Infrequent watering allows the top layer of soil to dry completely which kills off many shallow rooted weeds.

3. Mulch mow at the highest setting on your mower. Most grasses are the most dense when mowed tall. Bermuda, centipede, and bent grasses are the most dense when mowed at the lowest setting on your mower. Dense grass shades out weeds and uses less water when tall. Dense grass feeds the deep roots you're developing in 1 above.

4. Fertilize regularly. I fertilize 4 times per year using organic fertilizer. Which fertilizer you use is much less important than numbers 1 and 2 above.
   

You do not need to aerate again...ever, if you follow the steps above. Yes your soil might get hard again, but it is easily fixed by spraying soap and possibly by spraying molasses (jury is still out on that one).

If you kill the weeds, will you have anything left? If you want to kill weeds, I always suggest spot spraying with Weed-B-Gone. It works only on broadleaf plants like clover and dandelions. It does not work on grasses.

The soil test will tell you if you have acidic soil. It should also tell you which type of lime to add (if any) and how much is enough or too much. Some lime sources are much more effective than others.

Do the trees provide much shade? Of all the cool season grasses, only fescue has tolerance for shade.

Yes you should add organic matter. I would add it in the form of organic fertilizer rather than compost. Compost is good for replenishing your soil microbes, but if your lawn was neglected, then you probably don't have a problem. The problems come when the owner over applies chemicals. You don't have that problem. Just fertilize with organic fertilizer at any time and you'll be good. You cannot overdo it with organics like you can with synthetic fertilizers.

Thanks for the advice dchall.

This section of the lawn is 80% covered by vegetation. Of this 80% veg., approx 20% is undesirable weeds and moss... so yes, there will be some good grass left if I kill the weeds. Is there any advantasge to killing off the weeds now as opposed to sometime early in the fall or late summer? I know I should give myself at least 4 weeks after weed killer application to start the seeding. Or does that not apply to a post emergent weed killer?

The trees provide some light to moderate shade on about 50% of the lawn. The other 50% of the lawn gets just about full sun.

I don't know what type of grass is growing there now, but if I use tall fescue and KBG, to overseed and repair bare spots, will the lawn look funny? Will it eventually all blend together to look uniform?

There are mixes of fescue and KBG that go together. I don't know what they are off hand but the seed sellers know what they have.

If you kill the weeds, chances are different weeds will move in for the summer. I would leave them be and just practice taking excellent care of what you have. You'll be surprised how nice a field of weeds can look under proper care. Also get ready to fertilize on Memorial Day. That is your last chance for the summer (unless you want to try organic). Synthetic fertilizer and summer heat don't mix. The next opportunity is Labor Day.

Now is the time to ask, What do you want out of your lawn? Do you want a show place? Do you want it mostly green most of the year? Do you want to sponsor sports activities or run large, playful dogs over it? Your wishes at this point will really dictate which grass types to favor. KBG will not grow in shade. KBG will spread and fill in where there are bare spots. Some fescues tolerate some shade but they will not spread by themselves to fill in holes. The more uniform your mix of seeds the more uniform it will look. At the transition area from shady to sunny you will see a mix of KBG fading into fescue. You will likely need to overseed the fescue every year to keep it dense. Also the answer to the question above will dictate how much time you take preparing for seeding. You can seed into an existing lawn or you can kill everything and do a renovation. The full renovation takes more planning and longer execution so you really want to do that right. Seeding into existing grass is a matter of mowing short, power raking, blowing off all the chaff from the power rake, drop the seed, roll the seed down, and watering. You can do all that relatively quickly. Renovating takes at least another two weeks to kill the grass first.

With seed you get what you pay for. The seed you find at the box stores always has a small percentage of Weed and Other Crop listed on the guaranteed analysis. The weeds and other crop seeds you want to beware of are bentgrass and common bermuda. They don't have to list the exact species of weeds and other crop. All they have to do is list the weight percent in the bag. The problem with bentgrass and bermuda is the seeds are the size and weight of dust. Even a few thousandths of a pound will give you a lawn full of weeds. The best seed will have 0.00% of weed and other crop. Those will cost more but you don't have to start right away with a mess of tenacious weeds. Those seeds are sold on the Internet and at some really good seed houses.

Clover is only a weed if you don't like the look. When I was a kid you could not buy grass seed that did not have plenty of clover seed in it. When clover is evenly seeded across the yard, it looks very plush. It gets white flowers every week. Clover grows to 4-5 inches high and stops growing. It never needs fertilizer and can tolerate soil conditions that would set back normal grass. I think it has a lot going for it. When it looks bad is when it is just clumps of clover in the grass.

So back to business: If you are new, the place to start is to get your watering under control. If you are watering more than once a week now, stop that. Watch the grass so it does not wilt. If it does, then water, but the idea is to water longer, not more frequently. Your mileage will be different from your neighbors because of differences in soil, grass type, grass height, wind, and shade. Your performance will be different from mine due to heat, humidity, sunlight, and clouds. Oh and your sprinkler will be different, so you can't just say to water for an hour but you can say an inch. My setup takes 8 hours to get an inch of water. Fortunately my soil and shade conditions don't require more than a half inch per week. Before you water each time, spray with baby shampoo at the rate of 3 ounces per 1,000 square feet. Use the Ortho hose end sprayer with the big dial on it. They are sold everywhere. Soap will allow the irrigation water to follow to seep deeper into the soil. This step will save you a lot of grief. Deeper water penetration will stay in the soil longer and prevent runoff. The soil also benefits from improved microbial populations. Spray each time before irrigating for the next two months and you'll be good to go. It will soften your soil without aerating.

Anytime you feel a driving need to do something to the lawn, apply organic fertilizer. It will never hurt to apply even if you applied yesterday. Or you could spray it with molasses, milk, or even baby shampoo. These are helpful and can be done all at once or never, depending on your interest in this hobby. If you are interested in reading about the modern approach to organic lawn care, go to the GW Organic Gardening forum and find the FAQs. Scroll to the bottom of the list to find the Organic Lawn Care FAQ. It will point you to a low cost, low hassle approach to lawn care. I promise it will surprise you if you are unfamiliar with the topic. I stopped counting downloads on that FAQ years ago but since then it has spread all over the Internet forums. I'm guessing several hundred thousand downloads??? I know a lot of people who have gotten started with it and have spectacular lawns. I'll attach a motivational photo for you.

I have had this photo around for years since it was posted here at GW by a member named William. I had forgotten what his circumstances were and have recently posted that this was a KBG lawn where he had recently raised his mower height. Last week I found a text file I had stored with my original copy of the photo. I had this all wrong. It is a fescue lawn that William had converted over to an organic program. He was sharing the results. Here it is.

{{gwi:80292}}

This is not unusually good for an organic program following the 1-2-3 plan I posted earlier. You should expect this.
1. Proper watering
2. Proper mowing height
3. Proper fertilizer

Note that weeds are not a problem when you have this all under control. William has a weed in his yard. You can play Where's Waldo with it if you like. He was very happy, though.