If you are near Los Angeles State and County Arboretum (Arcadia), Huntington Botanical Garden or Descanso Gardens I am sure a visit to one or more of these would reveal potential selections for your project. Maybe the Sunset demonstration gardens in Menlo Park would be worthwhile, I haven't been there. If you are down near San Diego, Quail Botanical Garden (Encinatas, near the freeway) has shade plantings as well.

I'm all about plants that do something and don't need a lot of water. How about a rosemary? They're drought tolerant, flower, smell and taste great. Or a lavender plant. Or try some natives. My aloe vera likes a bit of shade here in The Valley, you might try some in that spot, it will spread and you can use it on your sunburn after the beach! I grow other succulents in part shade like jade plants (winter flowering). Boxwoods are slooooooooow in general. I have a mature hedge and decided I'd like it to be a little taller. I stopped trimming it a YEAR ago. It's gotten a little fluffier, with a few inches of growth on the sides. The top has sparse growth, the tallest sprig is only about 8 inches tall!

If you have room for 3 feet of plant width, butterfly bushes would be one choice. Lots of colors to choose from and the only maintenance will be to water and feed and cut them back hard in the spring. They even stay green through most of a mild winter. You can choose low growing ones like the Low and behold series or Adonis blue or tall ones ike Black knight or Royal red to suit yourself. Full size butterfly bushes can get wide, but they respond so well to pruning. No disease or pest problems. If you need something narrower, you might consider clematis stans or even obedient plant, if you want low, or a hardy bamboo if you want tall. I only suggest bamboo if the pots are sitting on concrete since the roots can escape through a drain hole and you do not want bamboo in the ground. If you put obelisks in the pots, you could also go with any number of vines and go as high as the obelisk you choose--clematis, trumpet vine, perennial sweet pea would all work. Or throw some morning glory or moonflower vines in the pots every spring and go with annuals. The obelisks would provide winter interest. The key is going to be what size and material you choose for the pots. In order to have the plants survive the winter you need a good size pot like 12 inches or larger. A resin pot will take less damage from freezing and thawing and will not dry out as fast as a clay pot inthe summer. If the pots are in unrelenting sun, the larger the pot, the less often you will need to water in the summer.

greenhearted, there are quite a number. Here are ones that work for me (acid, well-drained soil) some in shade and some in full sun, some in both. I'll just do a list and let you do some research as to what would be mostly likely to work where you are as far as light levels, hardiness, and soil pH and texture. Geranium 'Biokovo', G. 'Wargrave's Pink', G. 'Karmina', G. 'St. Ola', which I think are all types of Geranium x cantabrigiense. I have two types and they turn a deep red in winter. wooly thyme and variegated thyme a range of Sedums such as 'Angelina' and 'Dragon's Blood' Iberis sempervirens - the shorter forms are tidier IME Cranberry doesn't need a bog, just average acid soil Saxifrage if it's sunny - I don't know that all types are hardy or evergreen, and I am sorry that I've long since lost any memory of the particular variety I have. Veronica 'Georgia Blue' sun or shade European ginger/Asarum europaeum Epimedium - some are evergreen, some aren't; some spread, some clump Polygonatum humile/dwarf Solomon's seal I think is evergreen, but not sure. Good groundcover regardless Mitchella repens/partridgeberry Some types of Dianthus - My D. 'Greystone' is a lovely bluegreen groundcover that remains all winter Some coral bells and foamy bells: Heuchera, Tiarella, and their cross, Heucherella. How evergreen they are varies some, and how good they look in winter also varies along with how well they spread. Pachysandra, which includes a variegated choice, will spread, but isn't as rampant as the ones below in the list I mostly avoid. There are a few low-growing evergreen shrubs such as bearberry, some of the cotoneasters, lower-growing heaths/Erica or heather/Calluna if you have acid soil, and conifers such as low-growing junipers or Microbiota decussata, though all of those are a bit taller. I have learned to avoid aggressive groundcovers except in areas where they are well-contained. I hate having to remove aggressive plants from the lawn or other spots where I don't want it. You may find them useful depending on your circumstances: Vinca/periwinkle; Hedera/ivy; some kinds of Lamium; Ajuga has some rampant spreaders and some more well-behaved; sedge/Carex also vary lots, with only some evergreen and amount of spreading variable (I have C. 'Ice Dance' which spreads fairly vigorously).