I am a huge fan of using native plants in any design. Not only are native plants perfectly adapted to this geographic area, they also can help to restore the local ecology that has been damaged due to years of over-development and encroachment of invasive species. The Mid-Atlantic region is a major migration route for many species of birds, and native plants can provide vital habitat and food sources for birds, their insect prey, and other fauna. I am not advocating using only native plants (after all, what would DC be like without azaleas!) but even a few native plants incorporated into an overall design can have a modest ecological impact. If you are interested in learning more about protecting our environment and supporting the local ecosystem, I suggest reading "Bringing Nature Home", by Douglas Tallamy. In his book, he makes a very compelling scientific and aesthetic argument for using native plants in our gardens. I hold a Graduate Certificate of Professional Studies in Landscape Design from George Washington University, in addition to a BS in Biology and an MS in Biotechnology. I have lived and gardened in the DC area for over 30 years.