Don't plant the Empress tree, please. If you go through older threads here, you will get a lot of info - and opinions - about it, but basically, the Paulownia is invasive in most of the south, and isn't a good choice.

Tulip poplar is a good, tall-growing tree, that can grow quite fast - some of my seedlings are about 8' tall, after 2 years in the ground and a year in a pot from where I "weeded" them out of flower beds. I don't have any mature ones close enough to my flower beds to be able to say, but other trees, shrubs and grass, seem to be well able to grow under the ones in the pasture. Be aware that whatever the tree, there WILL be tree roots in the bed, but tulip poplar roots won't be as greedy as some of the maples, etc. You will just have to deal with it - planting mostly shrubs and perennials, and having annuals in pots will help - that way, you won't have to keep digging among the roots. If you plan the bed, plant things now, widely enough so they can be established when the tree roots grow out to them, and mulch and water, things should be good.

The main "problem" will be that the initial plantings will be in the sun, and only as the tree grows will you have the shade from the tree, which the plants will have to deal with. So you may have to re-do the bed in 4-5 years, just because what does well in the beginning won't be happy with the increasing shade, but the shade plants can't go in until there IS shade for them..... But, it will all work out, I am sure.

I agree that the Tulip Poplar is a much better choice for this area. And it does grow surprisingly fast.

Thank you. Any ideas about dogwood, weeping willow, or redbud (cercis canadensis)? Thanks

Willows take a LOT of water, so probably wouldn't leave much for any plantings under it.

The other 2 should be fine, but, while they aren't in the "slow-growing category", they aren't especially fast-growing, either.

I can live with that :-) Thanks

Redbuds and dogwoods are small understory trees. Tulip poplars are tall trees under which the smaller trees can flourish. A weeping willow makes an enormous tree--very wide, beautiful but very messy and one that sucks all moisture out of an area.

I'm not familiar with your zone, but other beautiful small flowering trees for my zone would include Yellowhorn (Xanthoceras sorbifolium), Seven Son flower (Heptacodium miconioides), and many deciduous magnolias with fragrant bloom in white, pink, and yellows.

I've read that crabapple trees can be planted under, and the 20' x 25' one in our back yard has no surface roots at all after 30 yrs. The only thing I've planted under it is a Kousa 8 ft. away from its trunk and didn't run into problems digging out any underground root masses (unlike my maples, which have awful roots above & underground).
There are lots of very disease-resistant varieties out now; some are dwarf like 'Camelot' (10 ft.). I understand 'Robinson' is one of the fastest growers. If you cut & paste this link, and scroll down to the chart, it gives a lot of valuable info on many of the new crabapples out there:
http://www.ces.ncsu.edu/depts/hort/consumer/factsheets/trees-new/cultivars/mallus_hybrids-table.html

If you are considering non-flowering plants, I would urge you to consider japanese maples. Many have knock-out spring, summer & fall color, can be planted under as well. They grow slowly as a rule, but IMO it's worth the wait!

If you have any arboretums or parks nearby visit them and see what you like the looks of and then do some research on the tree and see if it meets your needs.

FataMorgana

Thank you all. It's a good idea to visit a park to see what I like. I thought that the roots of ALL maples are invasively spread out shallowly. I do like Japanese Maple. I can plant it, if it is not like other maples.... Great

Well, you're right, J.M. probably do have shallow roots. I've seen many a photo of J.M.s in gardens amongst shrubs & flowers, but it may depend on exactly what you decide to underplant with. Three years ago I planted baby 1-yr.-old J.M.s from World Plants in a pre-existing garden with azaleas, yucca, roses, crape myrtles, daffodils, tulips, iris. My baby J.M.s are now 1-3 feet high and everything is co-existing nicely so far. Perhaps dwarf J.M.s (like Bene Maiko only gets to 6')could be planted in the place of shrubs in your garden scheme.

I've seen a bunch of shantung maple (acer truncatum) co-existing with azaleas so it doesn't appear to cause a lot of problem with surface roots. I recall someone saying that it is more similar to JM root system. It's supposed to have nice yellow blooms every spring but apparently, it have to be big enough first. Very nice new growth throughout the growing season (new leaves are always purple reddish before turning green)followed by nice fall color ranging from yellow to orange to red depending on genetics. It isn't that much different than JM except A LOT TOUGHER.