If between the hours of 10 a.m. and 6 p.m., it gets two or less hours of direct sunlight, then you can really only work with shade plants. Two to four hours of direct sunlight, then you can work with mixed plants. If it's greater than four hours in that area, then you can work with a full sun plant.

It's like a three-tier cake. If it's a window box, I definitely want something to drape over.

Line the window box with small bubble wrap on the inside because that will prevent heat being transferred over to the root system of the plant.

I usually suggest a perennial and something that stays evergreen.