ALWAYS avoid rototilling in preparation for a lawn. It sets you up for unevenness that takes a lot of work to fix.

What kind of grass do you have?

More importantly, where do you live? - because the party is at your house ;-)
If you live in SoCal, please be pretty specific because the entire range of zones is within a few miles.

Here are some basics of lawn care that might give you some ideas as to where you drifted off course.

1. Water deeply but infrequently. Infrequently means no more than once a week in the hottest part of summer and less frequently in cooler weather. Deeply means at least one inch at a time. You can measure one inch with tuna or cat food cans. Deep watering protects the turf from weeds and grows deep grass roots. I water my lawn once a week in the heat for 1-3 hours per zone.

2. Mulch mow your grass at the highest setting on your mower UNLESS you are growing bermuda, centipede, or bentgrass. Mulching returns the grass clippings to the soil to decompose and restore fertility. Mowing at the highest setting provides additional shade to the soil to keep it cool, helps protect the turf from weeds, and allows the roots to grow deeper.

3. Fertilize regularly with something. I like organic fertilizer but your choice usually has little impact overall if you are following 1 and 2 above. Just do something. So I can remember when, I fertilize on the major national holidays. Being in the south I start on Washington's Birthday and end with Thanksgiving. If you are farther north or at higher altitude you can start later. Also if you decide to use chemical fertilizer, then do not fertilize on the 4th of July.

If the drainage is that bad, you will have to do something about it. It is hard to grow a nice lawn if it is always wet. Also, do you have full sun?

I totally agree with dchall and eriocaulon and wish to add my two cents. Your statement that the ground seems wetter and soil is heavy with clay suggests an issue with the soil that you are trying to grow your lawn on. IMHO your soil is crying out organic matter. You need to amend the soil increasing the OM contained therein. Adding organic material to you lawns soil is the very good for whatever grows there. Compost is one method. Mulch mowing all your Autumn leaves into you your lawn is another. Changing from mineral fertilizers to organic fertilizers feeds the soil microbes which in turn feed the grass plants. I am a strong believer in the use of compost for problem areas of a lawn. A quote from member Scoot Cat in this forum: "An application of compost will do much more for your soil than just populating it with microbes. The compost, along with feed grains will continue pass through the microheard over and over, gradually releasing nutrients, conditioning your soil and forming humus. Fungal strands and grass roots will grow deep increasing the biomass below the surface. Moisture and nutrient retention will increase as the greater biomass acts as a sponge soaking up moisture and nutrients, releasing them when needed." I strongly agree with his statement. Here is a link with additional information on the benefits of compost. "Compost"
And have a look at the Organic Lawn Care FAQ linked below.
Bill Hill

Not sure the zone, but I live in Berkeley, not far from S.F. Bay, so the climate is semi-marine. At this point, the lawn is half crabgrass. I'm so pitiful I'd even be okay with that if I could just get it to grow! The lawn is surrounded by trees, so only the middle area gets what I'd call full sun. I live in a condo with some water nuts, so the advice about "more water, less often" is probably apt. So, to summarize, the advice I'm hearing is:
1) Reduce irrigation frequency, increase irrigation density.
2) Organic ammendments (compost, mulch).

So,would mechanical aeration help? What about sand to lighten the soil?

Thanks!

Yes and yes. If you live in a condo you might not have control over the water schedule. Getting control of it can be a nightmare. Mulch is only in the form of mowed over leaves, not actual mulch. The mulch has to disappear below the blades of grass. I call it micro-mulch (where can I trademark that word???) You also need to control mowing height. Where you're located you should have a cool season grass like fescue or Kentucky bluegrass. Again if the condo assn wants the grass mowed tight to the ground, just forget about having it look really nice. Crabgrass LOVES to be mowed close to the ground.

I was hoping you'd forget you asked about aeration and sand. Sand really won't help you if you need more living microbes in the soil. Mechanical aerating will give you a lot of peace of mind but it might not be the long term panacea you're looking for. If you aerate, aerate the snot out of it. Run it north, south, east, west, and every combination of compass headings you can come up with. I saw some pretty convincing pictures from a regular here. I believe he said he had about 12 holes per square foot when it was finished. Also if you have high and low spots in your yard, you can sweep the plugs removed by the aerator into the low spots to raise them slightly. Otherwise just leave the plugs where they land.

If you read the organic lawn care faq and wonder where to find a feed store in Berkley, ask anyone who owns a horse. Or call your local county sheriff. They know where all the horses are in the county.

The crabgrass does not surprise me but shade and crabgrass don't mix. Is the crabgrass growing in the sun? If not then you don't have crabgrass but probably have another pest.

And if you have that much crabgrass I'm going to suggest you try to switch your turfgrass to Kentucky bluegrass. It really needs sun, too, but what you have isn't working (can you thin out the trees??). The nice thing about KBG is that it does not thin out like fescue types of grass, it thickens up. Of course it needs some sun to to do that.

Just to set a goal for you, I'm going to post a picture of a fully organic KBG lawn grown with no weed killers. His only maintenance is infrequent watering and mowing high (and organic fertilizer).

{{gwi:79363}}

Now as to the crabgrass, it does not like deep infrequent watering. It like daily watering for 10-20 minutes per day. It also does not like shade. If your grass looks like that above, you'll note there are no thin or bare spots. There is no place for crabgrass to get hold. He could have crabgrass on both sides of that lawn but it cannot penetrate the dense turf. Mowing high and infrequent watering will take care of crabgrass in most lawns. Fescue lawns are different from most other turfgrasses and need to be reseeded every year or so for maximum density. It can be done but KBG is so much easier to handle.

Something else to consider if shade cannot be opened up is planting other ground covers. There is a dwarf mondo grass that looks like short grass that has curled over on top. It loves shade and will very slowly take over the lawn. I had two small patches in my grass when we moved in in 1992 and they are now 6 feet across. I really should do something about that, sigh.