I'll suggest a real favorite of mine, Angelonia. This heat and sun loving plant will bloom non stop, without any primping or prodding, up until the first serious frost. The purple one provides a color that really stands out in most gardens. Plant Angelonia (an jel O nia) at least twelve inches apart; they grow quickly to fill that space and more, and up to two feet tall. It's much loved by bees and butterflies, and even hummingbirds. No pest or disease problems that I've ever seen, but I don't have an irrigation system which can end up causing problems. Speaking of which, Angelonia is very drought tolerant once established.

I agree with Ricky and Tom. That's a tough area, but a rock garden with succulents could work. With that space, anything else might require constant pruning. One plant that I really like that you might consider is firecracker plant, which is happy without water. Irrigation would be complicated there, most of it would run down the drive. And you wouldn't have to worry about one of the main problems with firecracker plant _ it will root wherever it touches the ground, so it can spread out of control. Not a problem if it's bounded by concrete. It would end up draping over your driveway and your path some. But it's a can't-kill-it kind of plant here in Miami. It would fill in pretty quickly, but I don't know what would happen on those tiny corners. Attaching a link with pics. Ricky, Tom, thoughts? Y'all know this stuff better than I do. Here is a link that might be useful: firecracker pics

I am a little surprised at your planting. I would expect the azaleas to grow taller than the boxwood, making the boxwoods better to plant under a window. One possible companion plant is Astilbe. Prized for both foliage and flowers, perennial astilbes grow well in both open and dappled shade and even tolerate deep shade. The plants grow best under deep-rooted trees such as ash, oak, sweet gum and honey locust. Although astilbes will grow in sun, shade intensifies the color of the flowers and makes them last longer. The lustrous, finely divided leaves have a fern-like appearance. Mounds of green-to-bronze foliage become 12 to 18 inches tall. In midsummer, feathery plumes of flowers are produced. Each 8- to 12-inch plume tops a stalk 2 to 3 feet tall. Blooms last for several weeks. Of the A. arendsii hybrids, 'Peach Blossom' is light pink, 'Rosy Veil' is dark pink, and 'Red Sentinel' is rich, bright red. A white variety is also available. Astilbes can be used in flower borders, massed as a ground cover, or planted with spring bulbs to hide their fading foliage. They produce excellent cut flowers and can be dried for winter arrangements.

Scrap wood is certainly fine and it what I use in my garden. First make sure the box is located where it will get at least 6-8hrs of direct (no shade) sunlight, not daylight but direct sun. If you stand between it and the sun you will see your shadow. It looks like there may be some things nearby that will block the sun. < I should get a tomato cage for the tomato plant, right? Do the peppers need anything?> You can try the cages on the pepper plants, often the soil is too soft to support tomatoes in cages but can work for peppers which won't get as big or heavy. But for tomatoes I like Upright supports screwed to the side of the bed. I found some links from days gone by but feel free to search for more. http://forums.gardenweb.com/discussions/2162223/can-tomatoes-and-peas-climb-twine Vertical Support Not sure which side is North in your photo but make sure you plant your taller plants (tomatoes) on the North side. This is so the tall plants don't block the sun. Spacing can be taken from the seed packet - use the seed spacing after thinning since you won't be thinning. Draw it out on paper to see if you will have room for what you have planned. Keep a Garden Notebook. Each spring review what went well last year and what needs improvement. Winter is a good time to plan the next garden layout, plants, etc. Start small and try to avoid overcrowding. If you want more plants next year make another box. Cherry tomato plants tend to grow very tall (vines) and will provide lots of tomatoes. I am so glad you are teaching your son to garden. Kids are like sponges and learn so quickly then will ask you questions you never ever thought of to make you think AND learn. HTH and good luck. Any other questions?