Q. At my uncle’s farm, many years ago, there was a plum tree growing near the outhouse. The family never ate that fruit. Was that precaution necessary?

A. Maybe not. The tree would not have carried any disease-causing microbes from root to fruit. People have long planted fruit trees where outhouses used to be and eaten the fruit without apparent harm.

But only the fruit picked from the tree should be eaten, not fallen fruit.

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Some fruit trees can even be safely planted beside an active, properly maintained outhouse, in which human waste is mixed with dirt and ash — a sanitation system that is spreading in parts of Africa.

Ground-growing vegetables and fruits, obviously, should not be planted near a latrine. And septic fields and systems with septic tanks are risky settings for trees, too — chiefly because thirsty tree roots may invade the system, clogging or otherwise damaging it.