A picture would be worth a thousand words here. Bringing in soil might be good if you suspect the original soil has been washed away for some reason. Some trees will react to hard soil by sending their roots out at the surface. Then as the tree ages, the roots become larger and expose themselves above the surface. If that is what has happened, then adding soil on top of the natural grade will cause you drainage problems and could cost you extensively if water pours into your basement (worst case). Adding soil should be done with considerable forethought as to the consequences. Another thought on adding soil is to keep it lower than the root bark on the trees. Tree roots flare out from the base of the trunk. If you bury the root flare completely, then you are burying tree bark. Tree bark will often rot when it is below the soil level. It is best if you leave some root flare above the soil level to be sure you are not burying tree bark. Tilling is a bad idea for many reasons. One of the obvious ones is that you have roots everywhere. You can't till tree roots. A much less obvious reason is that tilling destroys soil structure by fluffing it up. Once it is fluffy it has to settle again. That process takes 3 years. When it finally settles it will settle unevenly leaving your surface bumpy. Grass seed should never be mixed in with surface soil. It always goes on top of the surface. Many people recommend "scratching" it into the surface but that is not necessary. Nor is covering it with straw. All you need to do is loosen the soil at the surface (1/16 inch deep) before you apply the seed, then apply the seed, and finally roll the seed down with a water filled roller (rented). Seed should remain at the surface. If you insist on straw, as goren said, be careful not to use hay. Hay is forage for animals and has seed in it. Straw is the left over after the seed is threshed out. New seed must be watered 3x per day at breakfast, lunch, and dinner for about 10 minutes. The idea is to provide enough consistent moisture for the seed to swell and open (germinate). Unfortunately these are the exact conditions that crabgrass seed needs. For this reason grass seeding is most successfully done in the fall after crabgrass has stopped germinating. Also grass sprouted now will have weak roots that cannot stand up to the summer heat and dry weather. That might not be that much of an issue in your area. Don't assume you have clay. Fill a mayonnaise jar half full of dirt. Then fill the jar completely with water and a drop of soap. Swish it around and let it settle. You will see rocks and sand settling immediately to the bottom of the jar. In an hour all the silt will have settled. At that time if you have clay, the water will be cloudy. Let it sit another day and see if the water clears up. If it clears then you do not have clay. Clay will cloud the water for days and days. There are several conditions of minerals that cause soil to seem to be clay when in fact there is no clay at all. Don't be too surprised by this. Adding gypsum without doing this test and a soil chemistry test can be a mistake. I disagree with goren on mowing height. The only grasses that need to be mowed lower than 3 inches are bermuda, centipede, bentgrass, and some zoysias. Kentucky bluegrass (which you can't grow in shade) should be no lower than 3 inches. Fescues and all the other grass types should be mowed back to 4 inches. Usually this is a mower's highest setting. Grass grown in the shade needs to be longer simply so it can photosynthesize. Can you post pictures showing the tree roots and one from a distance showing the trees with the canopy?

Jet Perennial Ryegrass. It is very dense, very dark green, fine bladed, and can be mowed down to 1/2" or 4" if you like. It takes the heat and drought as well, its only problem: Gray Leaf Spot. Now, if money is not an issue, you can spray chemicals and make it persits like a true perennial that it is.

it funny you should ask because I`m looking for the same thing and I live in a similiar climate. Evergreens are more difficult in my area now due to the government reintroducing deer. They can completely anniliate young evergreens. I have totally given up on white pines for that simple reason. White cedar aren`t tolerant of my regions drought. I like bald cypress, pond cypress,and dawn redwood. So far I haven`t had much luck with larches, but I`m not one to give up. Loblolly pine does pretty well. It tolerates extremely dry soils, wet ones and even the ones where no other pine here will live because of poor clay soil. There are better pines for less troublesome sites. It also has some problems with insects. I`m getting ready to post on just where I can locate just a few. So far all I have found is where I have to buy a thousand. Where they are native they aren`t sold much anymore due to insect problems. Maybe the problems aren`t as severe here. In an extremely cold winter they do suffer from wind-burn in my region but they always seem to recover.

Do you have a basement? Do you have some particular worry about the drainage around the foundation, i.e. some ongoing issues? Basically I would separate these issues and not think that adding a lot to your yard is going to magically fix the issue. The house probably should have had some kind of drainage (like French drains) around the foundation to deal with regular rain. "Flooding" could be a number of things but if it's the water table coming up too high, a yard that drains somewhat better isn't going to make that big a difference. So if that's your concern and you're really worried about it, consult a professional. You'll also want to look at your drainspouts and that they lead the right way. As far as amending soil for the garden part, if you really want to level things out it's going to mean adding a lot of organic material. This is going to depend what's available in your area, but wood waste, wood chips and wood in bulk are likely to be the cheapest. You may find local utilities (that clear wood trimmings around lines) may give away free. You can bury wood (hegelkultur) and add wood trimmings and chips either in ground or above ground. You'll likely have to repeat several times (the wood - any organic matter - will decompose and shrink over time). You'll hear that wood waste dug into soil may 'lock up' nitrogen for a while and make it harder to grow a garden - but over time the nitrogen returns to availability in the soil. It may take a few years but should eventually create a good garden soil. So partly depends on how big a hurry you are in. You can also do the way you propose it will likely just require a _lot_ of material. There's nothing wrong with doing a combination, either - all of the stuff will help. Sand is probably a bad idea. The more organic material, the more chance the soil biology will do some of the mixing for you. I'm mainly suggesting wood of various kinds as most likely available in very large amounts. As I said - the organic material/better soil won't magically solve drainage issues. It will help buffer rainfall some - less likelihood of pooling of water or standing puddles - but within limits if the soil deep down is all clay and/or the water table rises too high. This is pretty generic info - don't know anything about how bad your clay is (if you search here, you'll see lots of people have thick heavy clay soil problems), very little about how bad your flooding issues are, house construction, etc. There are more serious solutions to drainage and lots of info about ways to help, use Der Google. )