What city do you live in? Does it get 100+ degrees in summer where you live? If so, nothing will do too well in full sun (6+ hours or full afternoon sun). The sun is too intense and the pot soil just gets too warm. Conversely, if you can put your barrels in morning sun/afternoon shade, you can grow almost anything, assuming your soil, nutrients and water needs are taken care of. Don't give up on your lemon tree. It's hard to keep them looking good outside during winter unless you live in Miami or San Diego. If you think it can hold on for another month, I'd give it a shot of mild liquid fertilizer now. You will still need to address the hot afternoon sun problem though.

Welcome to the world of gardening! You've gotten some good ideas. Here are a few other things to consider. For color Katie ruella is a good little border plant. It's a dwarf and comes in purple, pink and white and will bloom in just about any conditions. Mexican Oregano blooms almost year round in those same conditions for me. Texas Betony is good. I see you already have Mealy blue sage that seems to be liking it there. There are other sages to consider. Also ornamental grasses such as the purple fountain grass you already have. Some grasses grow nicely under trees such as inland sea oats for me For something with a little height consider some of the Texas native understory trees. I think Possomhaw holly does very well in the Houston area. It has bright red berries in fall and winter. Mexican red bud stays small for me and blooms heavily in the spring. Anacacho Orchid Tree is a lovely little white blooming understory tree that butterflies love. You may have to make your bed a little wider to accomadate all the nice things you'll find to grow there. Sorry I don't have any experience with Virginia sweetspire. Beauty berry might be nice in the corner. It gets very large here in San Antonio in full sun, but in part sun would be smaller. Check out some of the plants on the site linked below plus a local privately owned nursery would be able to make more suggestions. Also visiting a botanical center and seeing whats growing well in similar conditions that you have is very helpful. Here is a link that might be useful: Natives of Texas

Combination of advice. The advice from the paint store fella is how the company advises their products be used. However, the clue is keeping a wet edge. If you let an edge dry, the next application will simply be over a dry area, and that is where the peeling can happen. So, the big IF---IF you can keep a wet edge, you should be fine. IF you cannot, you will probably have problems. There is where Jane's idea has merit. Apply stain early, when keeping a wet edge is easier. That will make the application area larger and you will get done faster. Or, wait for a cloudy, rainless day.

Agapanthus may be a possibility. They aren't native, but they come from a similar climate (southern Africa). When we moved to our house in Marin last year, there were many agapanthus lining the patio. We dug them out (actually a tractor did it) as we replaced the patio. Despite the digging out and all connected to creating a new block patio, little agapanthus sprouts still pop their heads up every now and then. At the fence line there are more periodic volunteers which get mowed and still show up later. That spot stays wet from neighbors' enthusiastic watering and underground seepage from the nearby hill. They have done fine in the hot, the cold, the wet, and the dry. The flower is very attractive, but so is the plant when the flowers are done. The ones in our yard were knee high, but they come in various sizes. Had we preserved the originals, we would have needed to divide them as they get dense. On the con side: clearly agapanthus are persistent, aggressive even. They grow on rhisomes, which is a plus and a minus.