Because I have been thinking so much about trees, I have also been thinking about shade. So many of us garden under trees here in New England, so we are very familiar with shade gardening. In fact, I remember distinctly a couple of decades back now (although it seems like almost yesterday) when my Mom bought a house, she asked for me to help with the landscaping.
Well, she was blessed with full sun. And I had been gardening in shade for almost a decade by that point. I had to completely reverse my thinking to pick out trees, shrubs and perennials for her. In addition, she was at the beach and had very sandy soil–not my heavy clay. It was really a total switch for me. Luckily we found some good garden centers where we could choose some plants.
But it always shocks me when I start thinking about shade–and how I might describe shade, for example–for a lecture I am giving. You come across the descriptions of “part-shade” as 4 hours of sun. That’s totally shocking to me because there are areas which get 4 hours of sun in my yard and I call that “full sun!”
For the record, “full sun,” is described as at least 6 hours of continuous sun. There are very few places in my yard that I have that–in fact, I think the only place that I do have 6 hours of sun is around my mailbox where I grow my roses.
But shade has its own advantages. The houseplants–even those that normally sit in my south windows all winter–prefer a partially shaded site once they’re outside and getting the benefit of true sunlight. And those that like less light prefer it under the shade of my dogwood, which actually throws quite a bit of shade, but still permits some early morning sunlight to get to the plants (before they roast on these midsummer days!)
True shade houseplants actually sit on my front stoop where the shade from the house protects them. Shade from a building is of course total shade–all light is blocked. Some ambient light filters to them from the front, but nothing gets to them from the rear–and they are completely happy and growing like that.
So all shade is not created equal–it helps to remember that whether you are gardening in containers or in the ground!
Gardendaze 
I’ve been on both sides of the “shade” fence here. At first I had too much, courtesy of the far too many oaks that were eventually, over the next few years, eliminated. So now I have the opposite problem, at least until some of my newly planted deciduous trees get some size to them: Too much sun! The only Full Shade area I have is under a large Japanese maple, which means it’s also Root-Filled Dry Shade. I haven’t done anything with that bed yet but when I do, it will need some really tough residents in order to cope with that situation.
The Spoiler was watching news coverage of some trees that had come down in several places recently. One had come down on a house and had rendered the house uninhabitable. He turned to me and said, “wow. We could get wiped out here.” It was very sobering. Luckily in the case of the homeowners in the news, they were at work when the trees came down, so they were at least safe.
Trees are a blessing–and then suddenly they are not–like when you are dealing with years of their accumulated roots. I have heard of people trying very small plugs of plants to get in between those roots, or trying to spread a very thin layer of compost first (but you don’t want to add too much for fear of smothering those roots).
With all the absolute beauty that you have created in your yard, I am convinced that you will be able to find a solution that will work.
Karla