My wife is on my case to get MORE LONG LASTING COLOR underneath our 60
foot tall maple tree. I have success on the street side of it that
faces east and gets morning sun, but the west side that is heavily
shaded is difficult. The tree is boxed by 4 landscape timbers, e.g. a
small square planting area 8 ft on each side with the 2 ft tree trunk
in the center (the box is only 4 inches tall or less). I have 4 sedum
(one on each side) and planted Ajuga a few years ago as a ground-
cover. At first she liked the Ajuga, but now says it doesn't bloom
for a long enough duration. She recently came home with 4 purple
plants. One each of: Salvia, Red Fox Veronica, Lamb's ear, and
Speedwell.
The Red Fox Veronica (Pink Speedwell) is almost dead and I just
moved it to full sun and watered it well. The needed location is
heavily shaded.

What are my options when it comes to perrennials or self seeders that
show color over the longest time in zone 4 (Midwest) in shade? Please
send as many ideas as possible as I get the idea I will have to try
several to make my wife happy.