Gardenia radicans is susceptible to nematodes, might that be what you are referring to? Camellias (the three primary species) can suffer from nematode damage, though I don't believe that it is particularly common. What kind of nematode was the culprit, if I may ask?

There really isn't much a homeowner can do to protect plants against damage from these little animals. They live in abundance in most areas. If we foster a healthy, balanced soil system....use mulch.....avoid soil chemicals and pesticides.....everything pretty much balances out. It's important to ID the species of nematode so that you can avoid replanting anything that might be susceptible back in the same area.