cynthia - I've tried loropetalum in sun and shade - in the deep shade it got leggy and sprawley, didn't bloom well, and the leaves greened badly, and it wasn't a very pretty shade of green - kind of muddy green. The one I have now is a Changs Ruby which is fairly compact and gets sun from about 9am to 1pm, and then light shade thereafter. It stay pretty compact, and the leaves color up better, but after it flowers I do have to trim back some of the longer shoots. I keep it easily to 2 1/2 to 3 feet tall. So it might work for you. I guess you want something evergreen? And is it small where only 1 plant can go, or do you have room to put several different things, and how tall do you want the planting to be?

Hi debndal. It's not very deep. Approximately 20 inches, and probably 12 ft long. I have 7 parsley plants in there side by side and their branches just barely overlap.

I hadn't thought of doing a mixed planting....duh! That leads more to more potential plants!

Thank you for the info about loropedalum, that is what I was afraid of. It seems that folks around here use that purple wandering jew. One uses Redentas and their window planter has about 9 spotted leopard plants. They get less sun. I don't think I want to water those.

Someone whose faces north uses caladiums, and that's a possibility, but again, I don't want to water them. So you see, this is why I'm living with parsley whose bottom branches are very brown.

Cynthia, I would plant sun coleus. I have some in pots that get full sun for a few hours and some with mostly shade and they do very well. They don't require a lot of water and add a lot of color.
I pinch off pieces and stick them in pots to make more. They are easy to propagate. If you want a start of mine I'd be glad to share with you.

Here is a link that might be useful: SUN COLEUS

Lantana is heat and drought tolerant. For the sunny side of your window box you might want to try one of the trailing varieties - they come in white and lavender, There is also another trailing lantana variety that's popular in the big box stores - Gold Mound; it's flowers are golden yellow. - June

Here is a link that might be useful: Trailing lantana

Hmm 20" is pretty narrow - Sun coleus is a great idea for texture and leaf color. Maybe calylophus, purple skullcap, scabiosa, in the sunnier area - maybe a crimson pigmy barberry in partial sunny area (thorns, but if you only have one or 2 you might still be able to wash the windows without getting scratched up. They stay small). Chocolate eupatorium, zexmenia for the partial shade, ruellia, helleborus, pigeonberry for shade? Keep a parsley or 2 for the cats. Just throwing out some ideas for year round color. I'd definitely do a mixed planting.

Thank you all!
What great suggestions. I love sun coleus in sun and shade, and I agree they are great in shade too. Not enough sun for lantana. I'm copying the suggestions for other shade areas.

I went to pick up 10 bags of mulch and some pentas. Talked to my favorite local nursery guy to see what he thought. I ended up with green wax-leaf begonias. Sounds boring, but they are enormous and the the pink undertone in the red ones goes with the pink brick and the bright green is a nice contrast.

These begonias are a new version call "Big" Supposedly they can get 1 1/2 feet wide and the leaves are almost the size of my palm.

It was a spontaneous purchase and I'll be back to the drawing board or ready for more parsley next winter.

Don't worry, I have 2 very happy huge parsley plants and some fennel. Any cats or eggs I spot will be relocated there.

thanks again.
c

Here's what I ended up with.

Here is a link that might be useful: Big series

WOW...those begonias are huge. I need to make a note to myself to try those next spring. I think they'll be gorgeous in your window box.