that I still shudder at now and then. But I can't remember the name of it.
A girl took her boyfriend home to meet her family. They lived on top a radioactive pile of whatever. The elder family members were whacko and dangerous and mis-shapen from the radioactivity. The family greenhouse was hugely dangerous due to man-eating plants, the family ate from the greenhouse, blah, blah, blah... I don't remember how it ended, but I would love to bump into that one again.
Yup, definitely an old b&w.

edit typo: onset of radiation induced whackoness?