Certified GKH Gardening Expert
Is that a shady or part shade location? If so, the heuchera and dwarf plumbago (perennial groundcover) would do well. St. John's wort needs part sun. Dianthus and hyacinth bulbs need a full sun situation. The heucheras would be nice because they are evergreen. If it's a shady site, hellebore is also evergreen. There are lots of dwarf hydrangeas now that bloom on new wood and can be kept short. Bobo hydrangeas only get 2 to 3 feet. I don't know how tall your Japanese maple will get, but small shrubs are also a possibility.