You can intermix them, but they do have different ways of growing. The semps send out chicks, the heuffs produce from the stem in tight rosettes. The heuffs have to be split at the stems, each rosette having some of the roots.
When I get home I will do an article on heuffs, I just realized there isn't much info here for them.
In this case more info is better.
Are you going to use some of the low growing sedum in the wall also? They are beautiful used that way.
