Gardening within the root zone of a large tree is always a challenge, especially one like the Liquidambar (sweet gum), with an extensive network of surface and feeder roots. The roots outcompete smaller plants for any available soil moisture and nutrients and the tree when in leaf will often shield rainwater away from reaching the underplantings. Plants best suited to this type of environment are those that will tolerate dry and typically unfavorable soil conditions. Whether they need to be shade tolerant or can be more sun loving will depend exactly on how much light reaches this planting area but they will all need to share the characteristic of being drought tolerant. And they will need help initially to get established, with frequent deep watering and perhaps some nutrient supplementation through fertilizer or a layer of compost. One of the things you could try - in addition to a better suited plant selection - would be to enlarge the size of the bed. Using the sweet gum as an anchor for one end of the bean shape, draw the shape out so that the opposing end is well clear of the canopy. While the roots will still be present, the area will be more exposed to the elements, receiving more direct sun and rain. You could also raise the soil level in this area, which will give the new plantings a better start than digging directly into the rooty, nutrient-starved existing soil. You just need to be careful not cover the entire perimeter around the base of the tree with additional soil, as this can deprive the tree roots of oxygen and eventually kill it. But raising in it one particular area well away from the trunk will have no adverse effect. And a larger planting area will carry more impact than a smaller "ring" around the base of the tree. There are lots of drought tolerant perennials (and quite a few shrubs) that will grow in this situation, especially in a zone 7 climate. Google up some lists or visit a local nursery for their recommendations. Smaller sized plants will establish easier than larger, more mature ones (and they are far easier to plant when digging through compacted, rooty soil). Most annuals tend not to be the slightest bit drought tolerant so you may not have as much success with them. And often the plants best suited for these conditions are not the showiest with respect to flowering so you may need to dial down your expectations and focus on foliage or other long term interest. Good luck!

I put thick layers of thick layers of wet paper (newspapers I had saved, telephone books, the newspaper type ads received in mailbox, etc.). I got it wet by soaking it in water in a big garden pull-type plastic container. I did that because I had read that it would start breaking down much faster if it was wet. I then covered with cardboard and watered it well, too. Because we have constant wind, I did have to put heavy stones in strategic places so the cardboard stayed in place. But when it all composted, I had wonderful earth to plant in.

I am (slowly) getting there. When I first started to garden, shrubs seemed a terrific wheeze to effortlessly fill space. In short order, my tiny garden was filled with weigela, escallonia and other slightly dull but large and easy specimens. Naturally, after only 17 measly shrubs, the garden was stuffed and I was bored, bored, bored. Out they came and fell into a continuing infatuation with seed raised annuals...and later branched out into perennials. When I got an allotment, I was fixated on huge roses and rapidly filled the entire plot. Fruit gardening probably opened the door again and when I actually got some acreage, shrubs have been appearing on my radar a bit more frequently...although I have struggled a bit with dismissing prior assumptions of innate stodginess. Aso, having a very alkaline soil has rendered some really choice shrubs unusable (enkianthus, disanthus, fothergilla, zenobia, eucryphia, even cornus...but otoh, lilacs, philadelphus and deutzia fit well in the not very manicured woodland spaces, while lavender and salvias play happily in the perennial borders...but yep, this is an area ripe for exploration (for me).

This book is definitely one of my favorite garden reference books. I also recommend 'Bringing Nature Home, How You Can Sustain Wildlife with Native Plants" by Doug Tallamy, & "The Midwestern Native Garden, Native Alternatives to Nonnative Flowers and Plants" by Charlotte Adelman & Bernard L. Schwartz.