Well, the first thing to know is that you have the wrong soil for a lawn. If you want to keep it, you're going to have to lime it every year to make it more alkaline.

Oaks are pretty tough to grow under - there are whole discussions devoted to growing under oaks.

One way to rehab it is to cover it in mulched leaves and coffee grounds for the winter. You could cover the whole thing in a few layers or cardboard and either put new soil on top or do a lasagna bed, then reseed in that.

Lawns tend to go dormant here in the summer instead of the winter, which I hate, so you think about that when you choose the new grass.

Before you do any of that, though, check out some oak threads and see what other people have done that has worked. Good luck!

Gord, you might find this treatment ( John Caine, staff designer at Joy Creek Nursery ) interesting - I've used it for areas of poor drainage, but haven't had reason to do an entire lawn this way.

It would help with your clay and drainage, but I can't speak for the shade you are encountering from the oak trees - I don't have the oak.

If you are new to the area and enjoy gardening, you might enjoy the display gardens later in Spring at Joy Creek - they aren't far from you.

Here is a link that might be useful: Improving lawn drainage

gord
You have my sympathies. I have the exact same lawn. Under a big white oak, & soil so nasty that it was really bumpy to walk on. Full of moss. I've been here two years & I tried aerating & applying compost & lime. A big waste of money & time. I would take the advice of both of the people above. I finally put a layer of cardboard down over my lawn this winter (free from the grocery store, or you can use your moving boxes-just take off all the tape) & soil that I had, but any compost-able material will work. Lasagna gardening as mkirk says. There is lot of info on that on these forums. You rake out the lumps and stones, roll it with a weighted roller (which you can rent) and just seed it over. This way you're not tilling under the oak tree & disturbing it's roots. Also less labor for you! Anns suggestion to add fine grit gravel is an an excellent idea. I'm not sure about the compost tea. I don't think planting under oaks is as dire as mkirk says, but they do tend to suck up a lot of water & nutrients from the soil. I plan to reseed with white dutch clover myself, which never needs fertilizer & is much more drought tolerant. You will appreciate that when you see what the water bills are like in Portland. I have two friends in California with all clover lawns & they're beautiful, & even hold up to little kid traffic. I plan to seed the clover in March. It will be interesting to see how it does.

Thank you for the tips. I will do some expermenting and cross my fingers.