I have a problem with a stand of 3 mop tops in my front yard. After 12
months in the ground they have growth but it is very spindly and not
lush at all. Almost anaemic looking. They do have fresh growth
visible, but they do not appear to have matured much from when they
were first planted. They do not get a lot of sun on the South side of
the house where they are planted.

Another mop top from the same batch is planted on the North side of the
house is doing very well in full sunlight.

Is the sunlight the problem?
Will the robinias come good eventually or should I bite the bullet and
get something else?
What could I get that would replicate the effect of the raised coverage
that the robinia provides?

Thanks.
Steve.