How To Design a Garden Border?
 

I intend to design a garden border for the area in front of my house. Currently, there are 4 evergreens evenly spaced and about 2 feet tall with day lillys in between them.

While this looks good for part of the year the rest of the year it looks like nothing. I am looking for some ideas on how to go about designing this border.

The area is in sun for pretty much all of the day, I live in Strasbourg, France. The area is about 40 ft long and about 3 feet wide, but could be made more wide for the right design. Thanks.