"Sa culture est facile."
In French, I understand that we are talking about a plant or vegetable or flower of some kind, that you can easily grow.
It cannot mean "la culture" in the sense of "knowledge" because "facile" would not mean a lot with it.
If this is supposed to mean growing a plant, then I don't think culture is right (as they demand) but that it should be cultivation. (best translation of course would be "It is easy to grow/cultivate").