Is it full shade all year? You could do caladiums for summer, but they need regular water. Bulbs are nice because they don't need much in terms of nutrients and trees are greedy. But, they need to be replanted for the same reason.

How much sun do you have? I have a magnolia that is very greedy, but I get sun. I put in cacti and have snapdragons that have return twice now. Also, wood sorrel.

Can't wait to read the suggestions.
c

In my years of gardening I have found that planting under large trees is usually challenging. Not only do the plants have to compete for moisture, there is generally little soil available due to the feeder roots of the trees. I have found that planting bulbs or very small plants (rather than gallon-size) are easier to plant in these conditions. You may try shopping in the natives section of your gardening center as these natives are more likely to work well in these conditions. The key is to find something that will thrive, rather than survive.
Molly

We've used Turk's cap (malvaviscus arboreus var. drummondi) under the dense shade of a fruitless mulberry with good results. They will grow to ~4ft in shade if left alone, but can be kept trimmed to about 2ft which may fit your space.

Cedar sage (salvia roemeriana) is a smaller option. It grows naturally under cedar (juniper) trees. We have some growing under a dwarf peach.

We've used columbine (aquilegia canadensis, a. chrysantha) and pigeon berry (rivina humilis) under the more dappled shade of crepe myrtles.

Non-natives we've used under trees include pink oxalis (probably oxalis crassipes) and bearded iris, though iris does not bloom reliably in heavy shade.

Forgot to mention scarlet sage (salvia coccinea). I cast some seed left over from another project under our orient pear tree last year. The photo was taken just as it started to bloom in June. Unfortunately didn't get a shot in full bloom, but shows how robust it was above the tree roots even without being properly thinned.

Was intended as a temporary filler, but looks like it is coming back, so will give it another year. What's nice about it is that it does well in dappled shade and blooms from fairly inexpensive seed the first year. Only negative was that it required more water than St Augustine wherever it got more than an hour or two of direct Sun.

Are you dry or humid?

Under Live Oaks in Austin (dry) I planted Columbine, Blackfoot Daisies, Purple Trailing Lantana, and Vinca (depending on the sunlight--is this on the North side, or the South side of your house?)

In Houston (humid) I only have Oxalis planted, but my neighbors have: Liriope, Spider Lily (Hymenocallis), Turk's Cap, Lantana, Ajuga, Ruellia, Impatiens, and Indian Hawthorne.

Live Oaks have thick, shallow roots & they suck up all the water, so even in wet climates it's best to plant shallow rooted plants that tolerate shade & dryness.

I have alot of oak trees in my yard. The front rows are gerber dasies, cycleman, and snapdragons, with alot of amaryllis bulbs and oriental lillies that come back every spring. In the middle of the beds I have variegated ginger, holly ferns, and red leaf ti plants. In the background I have larger plants, like potato plants, and in areas of dapple shade I have planted iochroma,brugmansia and some tropical hibiscus. Variegated rubber trees, variegated iron plants caladiums, impatiens, and african hostas do very well in full shade .I have sandy loam soil. Barbra

That's interesting, burntplants, I have blackfoot daisy, trailing lantana, and lantana in full sun. Granted, it's the east side of the house, so they get late afternoon shade, but.... My Turk's Cap and pigeon berries are in part sun to dappled shade under red oaks on the opposite side of the house. The latter haven't bloomed yet, but they're only going into their 2nd summer. Iron plants would work well, I have some in a back corner that rare if ever gets watered and they're perfectly happy. I think. :)