In general, everything I know and have read says NOT to plant trees near a septic tank and leach field - shrubs and perennials usually can be planted with no problems, but aren't "shade plants". If the septic system is there, then I think you will have to either decide that the leach field may be damaged and need to be replaced down the road, and plant regardless - which can run into BIG bucks, and probably damage the tree roots to where they need replacing - or find another way to shade your house. Window awnings are a traditional means of shading at least part of the house. You could also build a porch, which would shade at least the lower half. You could plant a pergola, plant it with vines, and let it shade the house - how much depends on height, width and style. You could put trellis on the side of the house - spacing it out about a foot, to allow for air space for circulation and cooling - and plant vines or train espalier trees on it. Since you say this is the western exposure, and most of the heat from the sun will come from the Southwest, can you plant something more to the south that would be out of the leach field area and give enough shade to at least part of the house? Some oaks, and tulip trees, can grow pretty fast, given the right conditions. A male sweetgum is speedy-growing, also. And there is always something like a thornless honey locust, which will give lighter shade.

My purpose for the retaining wall is two-fold. Primarily to keep our 60inches of annual rain from washing dirt off the mound I planted the tree on and into the low area around the tree that needs to stay low enough to drain water from around my house. I want the low wall to be visually appealing so I plan to match it with the rock wall (part of an outdoor shower). The bonus for the sturdy wall is that I can use it to help support a freeze cover during cold winter nights. My main purpose for posting was to get input from folks with mature Dancys to see how big they get. I'm guessing mine won't get as big as some since my winters will be a little rough on my tree. I'm in Zone II, it's recommended for Zone I.

15'-20', you want essentially a shrub limbed up, not a tree, what is commonly called a "Patio Tree" would be in that size range. "Small" trees are usually considered to be in the 25'-35' range. When you go to a nursery and look at the label of a tree or shrub, and there's a size, that size especially for a tree, is the size after 10 years. Trees keep growing. They are not like humans and stop growing at a certain age. Stay away from showy flowers, if you don't want litter. Ditto for deciduous unless you want it to drop all its leaves in winter. Metrosideros 'Springfire'. Some of the selections of Pittosporum tenuifolium that are smaller than the species. Citrus, if you want to pick the fruit. The Eriobotrya delflexa, Bronze Loquat is a well-behaved patio sized choice. Crepe Myrtles are very attractive and they come in all sorts of sizes, but they do drop their leaves in fall and the flowers while beautiful end up on the ground. Before you make any choice educate yourself. An inappropriate tree can end up costing a lot of money to remove.

I take it that the stone mulch area is roughly centered around a tree? I would clean up its shape such that it is circular. I would try to hide the odd detail of "crying" trim at the windows. (I don't think it's an enhancement.) (FYI, they are domes, not balls.) Would also enlarge the steps and landing, planting nothing in that area exceeding the floor height.