Question
I live in the Philadelphia, Pa area.
I would like to plant some plants on top of a 2 foot high retaing wall.
The soil on top of the wall is about a foot deep with stone below.
I would like  some plants that will live year round so i don't have to put plants in ever year.
What would you recommend that won't grow to big ?
I would like them to be no bigger than 1 foot in diamater.
If possible is there a plant that would also flower ?
Can i plant them now or do i have to wait for the Spring to plant them ?

Answer
With winters, it is tough to have a "year-round" performer...but here are a couple for Zones 6 & 7:

-Barberry (red leaves/holds form in the winter: recommend 'Crimson Pygmy' or 'Kobold', as they won't get bigger than 1'),

-Prostrate Junipers (J. chinensis 'Parsonii', J.c.'Sargenti', J. conferta, J. horizontalis 'Blue Carpet/Blue Creeper', etc.), or

-Compact Holly (Ilex cornuta 'Rotunda', etc.)

-If you don't mind  "empty" spots within the planters in the winter and a wonderful spring flowering display, consider adding bulbs like Daffodils or Tulips.

Hope it helps ~M