All, I'm compiling a listing of hosta-friendly trees for a "Fact Sheet" that we plan to post in the updated AHS web site in the near future. Although I have a few favorite trees that work for many of us in the Northern Hemisphere, I'd like to hear what others believe. I do have the two previously published articles from the AHS Journal and they are a good start. Here's my short list that I'd like input on or additions. Thanks everyone:

Oaks - deep roots and high canopy
Pines - can grow hostas under them although the pine trees do pull a lot of moisture from the soil and drop needles often
Other Conifers - ?
Maples - Japanese maples work nicely, red, silver and Norway maples, too many surface roots
Dogwoods - are great companions for hostas
Elms - work well
American Persimmon - work well (if they do not bear fruit that is)
Ginkgo Biloba - also work very well (male trees only!)
Willows - can grow hostas under them but expect root competition
Flowering Pears - not sure how they will do long term so would like to hear other's experience

I look forward to hearing what other's have found to be the best partial shade providers for their hosta gardens.

Here's a few more tree types that hostas grow under without problems- these were listed in Rosemary Barrett's book "Hostas" from 2004.

Birches (Betula)
Tupelo (Nyssa)
"Handkerchief Tree" (Davidia involucrate)
Eastern Redbud (Cercis Canadensis)
Sweetgum (Liquidamber styraciflua) (I find these trees as too messy with their seed droppings)
Dawn Redwood
Swamp Cypress
Magnolias
Ornamental Cherry

Roger,
Dogwoods may not have root competition, but in Western Washington, when hosta need more water, the dogwoods don't want that much water and we have problems with the dogwoods. I don't know if that is the case in other places, or with all species of dogwoods.

Thanks for the additional insights Carol. I have both Florida and Chinese dogwoods that are thriving with my hosta collection. This area averages about 36 inches of rainfall per year and I have an irrigation system that runs a couple times per week. Perhaps I'm right at the sweet spot for both plant types to survive in the same garden beds.