Hi pinkgator, Can you be more specific about where you live? Is it zone 9a or 9b? Makes a big difference to some of these plants. In your choices, astilbe is unlikely to do well as it needs more cold. Philodendron you have to look up the type individually for cold tolerance, but if you are 9b, there are many types that would work under your oaks. Leather ferns need a lot of moisture and would be unlikely to get that under oaks unless you sprinkle quite a bit or are able to water it with a hose regularly. Liriope are likely to do well. Caladiums are tricky. If you live in 9b, they have a decent chance of coming back each year. In 9a, I doubt it, but you could plant them as annual bulbs and they would be beautiful under oaks. I am in 9b/10a Sarasota, and I have loads of oaks. I have variegated ginger, understory palms (chinese fan palms, wallichias, arengas, cabada and several others), many types of philodendrons, bird's nest anthuriums, landscape begonias, white bird of paradise, firespikes, pentas, macho ferns, fishtail ferns, holly ferns, heliconias, cast iron plants for extremely dry, non-irrigated areas, beautyberry bushes, wild coffee, brunsfelsia, cycads (dioons, encephalartos, zamias, coonties), powderpuffs, crotons, acalyphas,shrimp plants, justicia golden flame, and many others I'm sure. The trick is to not disturb the roots when you plant, choose something that won't require much irrigation (live oaks can decline if they get pampered too much with water, thick mulch, added soil on top of roots), and add as little as possible in terms of additional soil or thick mulch. I love Meem's garden (Hoe and Shovel). In that photo you see variegated alpinia zerumbet (ginger), liriope, dianellas, landscape begonias (red and large round lily-pad types), holly ferns and saw palmettos. Browse her site and you'll get loads of ideas! Good luck and have fun. Anna

I don't know pin oak, but I do find it mentioned in lists of trees unsuitable for underplanting with rhododendron and azalea....it's on the list as an unsuitable associate, reasons for that grouping of trees are: too dense or fiberous rooted. Have you dug around theplanting area under your tree to see what, if any, root competition there might be? Are the lower branches drooping in form so that they exclude too much light? Sometimes these larger trees can really rob the soil of nutrients and water more than we realize...do you mulch with compost or organic plant remains? I'm growing many oriental hybrids, foetidus, macrantha in my acidic clay. About once every 12 - 18 months, I push a stick of plain blackboard chalk down in next to each plant for a slow release of lime (three sticks for a large clump). Seems to work very well, and I don't have to be concerned about changing the PH of an entire planting area and making the acid lovers unhappy.

There really is no grass ( turf) that does well under oaks. Oak trees don't much like grass under them either. From the link St Augustine For Florida Lawns "'Palmetto' 'Palmetto' was a selection found by a Florida sod grower in 1988 and was released in the mid 1990s by Sod Solutions. It is of intermediate growth, with shorter leaf blades and internodes than many other cultivars, but is slightly larger than the dwarf St. Augustinegrass cultivars such as 'Seville' and 'Delmar'. It has a nice growth habit and does well in full sun or partial shade, but not in dense shade. It is sometimes referred to as drought-tolerant, but research has not shown that it has any greater degree of drought tolerance than other St. Augustinegrasses. It often has problems with disease, particularly in Florida's humid environment. It tends to have a lighter green color than many other cultivars." The link below has good info too. Here is a link that might be useful: Growing Turfgrass in the Shade

The most shade tolerant varieties of St. Augustine are Bitterblue, Deltashade, Captiva, Delmar and Seville. Floratine, Classic, Jade and Raleigh varieties also do well in the shade. Similar sounding Floratam and Floralawn are NOT as shade tolerant. All St. Augustine varieties are more shade tolerant than other lawn grasses. Tree leaves are meant to be the mulch that prevents other plants from growing. The leaves break down to feed microbes which make soil nutrients more available to the tree. The problem with live oak leaves is that they are leathery and take much longer to break down, and they smother any emerging plants when they drop in the spring. I have had good results with Holly Fern (Cyrtomium falcatum) under my mature oak. I do have to water these twice a month in the summer in Central Texas.