Hey chicamarie,

You might want to go to page two of the messages listed on this site and look at the thread "what to plant under/near a cedar tree". There is some info there that will likely pertain to your situation. Generally it is a bad idea to add soil around existing trees. Here's one of the responses to that thread, posted by by gardengal48:

"I'd like to know more about this raised bed. How big is the bed and how much is it raised? Does it go all the way around the tree? While an established cedar will have a root system that will extend far beyond a raised bed, it is NOT a good idea to raise the soil level around a tree by any significant amount. Or to increase the soil level around the base of the trunk. It can smother feeder roots and starve the tree of oxygen and moist soil or mulch against the trunk can promote rot. It's not necessarily an immediate result but you can kill or seriously compromise the health of the tree by doing this.
Under normal conditions (no raised bed), planting under a cedar calls for plants tolerant of dry shade. Obviously various natives like salal, mahonia and sword ferns will work. Geranium macrorrhizum is an excellent choice. So is lamium, the vinca, Euphorbia robbiea, dwarf sarcococca, epimediums and wintercreeper (Euonymus fortunei ctvs.). Dry shade is not a situation that encourages a lot of showy flowers -- look for your color in foliage rather than flowers."

Something different I have under my maples as opposed to under my cedars is patches of Anemone nemarosa, an ephemeral plant that grows from rhizomes. It comes up in spring, is covered with flowers, then disappears by summer. That would mean the ground would be bare from summer to early spring. But some annual could grow there in that time. I just have the soil bare, but other places things grow up in that spot but are not there in early spring when the Anemones are blooming.

Other plants I use-
*Viola labradorica, dark leaves, purple flowers, self-sows modestly.
*Hakonechloa, Japanese Forest Grass, yellow or variegated forms
*Autumn Joy sedum, tall pale green succulent, lovely, won't necessarily bloom in shade
*Oxalis oregana, or the one I have has pink flowers, don't know the species name
*Wintergreen, always looks great, white flowers and red edible berries
*Oregon holly grape, Mahonia, which comes in short and tall forms, and has an edible berry.

I live in Portland and have some extra Sedum 'Autumn Joy'

I also have muscari and lily of the valley which are invasive but would certainly work.

We also have a large maple; a Norway maple with its very shallow roots. It is difficult but we have gardened a quite large bed somewhat succesfully under it for nearly 20 years (and the former home owner for the first 20 years of the tree's life).
- Around the trunk is a good collection of skimmia which have been there for at least 25 years. They do well in the greater amount of shade right neear the trunk.
- our favourite under that tree is a large collection of early spring bulbs - snow drops and glory of the snow (chiondoxa) that have been there for over 20 years and always give an excellent show. The key to their success has been an addition of compost every year (either maple leaf mold or composted bark mulch. I believe that they do better with the leaf mold). In fact, over the years, the bed has been raised by about a foot or more b/c of the addition of the compost. B/c it has been gradual there has been no harm to the tree; indeed those greedy roots always move into the new compost quite quickly
- Sometimes tulips have done well for a few years on the sunnier side of the bed but have never lasted long. I may try again with species tulips to see if they last longer
- summer is more difficult b/c the bed is so dry. Those fibrous maple roots always move up near the surface and suck the soil dry. Some years, when I am willing to water frequently, tuberous or fibrous begonias have done quite well. The past couple of years, I have been surprised to have some good success with hosta (the 'June' variety which can take the hot afternoon sun that comes in on one side. They do need a good addition of compost (which also helps the early spring bulbs) but the hosta seem to be rooted deeply enough not to need watering too frequently.

Some people have asked why we keep such a difficult-to-garden under tree in our front yard. But it is not impossible to grow under it and it is a reasonably attractive, large tree. We love the shade that it provides the house on warm summer afternoons and evenings.

Thanks for all the good advice. I think I might plant shallowly with a good layer of mulch and compost and see how it goes. Another source about planting under maples suggested Epimedium, which looks like a good for my yard. They also suggested Japanese Painted Fern.

I'll take a gander around Portland Nursery this weekend and do some cost comparisons.

Thanks!
Christy