I planted several apple trees on the dike of a pond and others on a considerable slope. I had my best luck mounding the soil and planting the bare root tree actually above grade. My soil is quite sandy in some areas but the only amending I've done is adding some richer soil from a different area on my property to the mound soil. I mulch heavily with woodchips and water if it doesn't rain for 3 weeks or more. I don't know why the mounding approach seems to work so much better but the results have been pretty consistent. the only negative I've encounterreed is that the semi-dwarf trees on mounds take some staking to keep them growing vertical.

You should search for several previous threads on gardening under trees--also Google results. The silver maple is a real challenge, but things like hostas, bulbs, daylillies, some groundcovers and other things can work. Most success is had with planting in small pockets and with plants that tolerate dry conditions (hostas will do so once established and if not in sun). What you need to remember about planting under a tree with aggressive surface roots is not just the idea of adding thin layers and using loose organic materials (shredded leaves, grass clippings, fine bark) rather than dirt--although I would not recommend placing 6 inches at once--it's that you won't ever build up significant depth of good "soil" because the tree will extend its root system into what you layer on top of it. So your resulting bed will always tend to be a mat of roots and will not turn into inches of nice loam as will a regular lasagne bed elsewhere. So when you add a layer of mulch, it will be a layer of mulch at first, into which you typically can't plant much, and then a year or so later, the broken down part will be tree root heaven. Another unintended consequence that you should be prepared to deal with is that weeds will grow better the more you improve the soil surface, and will often grow better than what you want planted, so sometimes you turn a bare-ground, rooty area eyesore into a weed patch eyesore by adding more nutrient material to the surface. Also, the maple whirlies will take root easier. So, take a look at what part of the bed will be mostly silver maple, versus other, and don't plan on any kind of lush flower garden under the maple. Another idea to consider is using containers under the trees. Sometimes you can establish a groundcover for unity (tying the trees together) and then nestle in container plantings, both for height, and because by avoiding root competition you can grow a lot of things--shrubs, annuals, perennials--that you could not grow directly in the ground.

If you decide to modify the clay with sand, remember you'll be working it roughly 50-50 and it adds up. A thousand square feet of clay to remove and replace, four inches deep, is twelve heavy cubic yards, so it's good to avoid carting stuff away. As a rule of thumb, think of sand for drainage and organics (tons of it!) for growth. Two separate goals. If you do go the French rubble drain route and use an imbedded tube, look into local conditions concerning using weed barrier/landscape fabric to guard against finer materials seeping around the gravel/rubble. It can get in the way of drainage, even at what might seem to be a super slow rate. Here, in our very arid ground, I wrap a perforated three or four inch plastic pile with sunscreen when I bury it in the fill, so if the fabric/pipe clogs the fill might still drain and vice-versa.

"Jap" is a pejorative dating back to the Second World War. Weeping Japanese lace-leaf maples of the size shown here are worth thousands of dollars on the retail market. Specialists in large trees catering to the demand for instant landscaping here "mine" them from old properties and re-plant them elsewhere, getting again, thousands of dollars for them in the process. If there is one of these kinds of operations working your local area you may be able to get one of them to take yours away for free, if nothing else. Of course, they may want to be able to drive up to it with a machine and scoop it up all in one move. With the tree right in front of your house, with buried utilities perhaps present and a lawn you want to keep this may not be feasible. If you are wondering the taller shape shown in the Dig Doug cartoon would be achieved by installing an adequate stake and training the existing specimen up, to be more tree-like. And visually effective.