My old neighbor used to have a multitrunked one he'd planted about 15' from the front door. He always said he put it too close, and even though they were pretty they were a nuisance. They shed bark and leaves and each year some sort of caterpillar decimated the leaves til they looked ratty. I'd think in small confines you wouldn't want them. I don't know how much it dried up the ground, but they do tend to grow where it's watery in nature, which would indicate to me they're thirsty. I know he didn't have anything growing under his save maybe some liriope. When he left the new neighbors cut it down, along with nearly everything else.

What about redbuds? Not sure if they have shallow roots or not. I know the maples and dogwoods do. There are things that will work under them, though- my bloodgood maple has sedum, scilla peruviana, setacresia (purple heart), columbine, veronica, black liriope, dianthus, heucheras, goldflame honeysuckle, a climbing rose and some other odds and ends under it, and it's about 15'+ now. Cyclamen and hellebores would do well too. I have lots of little species bulbs and daffs in there that do well, too. You want to pick things that can take dry semi- shade if you go that route. Most all trees will want to run roots into the soil. You can get around it some by putting the plants in pots and sinking those, though that isn't what i did.

Hmm. I'm looking for something taller than a redbud, maybe in the 30-40 ft. range. Any other suggestions?

How tall is that bloodgood?

I have a sweet bay magnolia (magnolia virginiana) growing beside a patio with plants underneath -- gardenia, heuchera, perennial geranium, winter daphne, colocasia, nandina. So far, all is well. We saw one growing right up against the winery building and brick walkway at the Biltmore Estate Winery and decided to plant one. Very fragrant in May and semi-evergreen (ours has been evergreen the last two winters). Loose habit for filtered shade. Pretty tree.

There is a variety that will grow to 40 feet.

We got ours from Dickinson Garden Center in Chapel Hill.

Hope this helps,
Cameron

Here is a link that might be useful: photos of my magnolia

Do some research as to how big bloodgoods get. I think it'll be too wide for your space when & if it gets tall enough though, based on mine so far. It's about 2/3 as wide as it is tall right now.

It may be tough to find a 40' tree that will still fit comfortably in a 20' wide space. You need to be considering columnar types for that. JCRA has a new columnar liquidambar (sweet gum) that's very pretty. I think it doesn't get the gumballs, either- a very nice bonus! I agree with cameron- sweet bays are lovely.