A commercial site we maintain has insisted that we plant Pacifica Red and White Vinca in their beds (7 consecutive years). In recent years the plants have gradually been less vigerous and healthy. I believe there are site conditions (overhead irrigation, no crop rotation to name a couple) affecting the vinca. WHAT WOULD BE SOME ALTERNATIVE COMBINATIONS THAT A CUSTOMER RESISTANT TO CHANGE WOULD FIND ACCEPTABLE? I dont want to reinvent the wheel, just keep them happy! site conditions are: commercial setting, overhead irrigation, poor to average soil (clay based), moderate drainage, FULL sun, parking lot beds.