Parashas Eikev · Passuk 11:11
but the land you are about to cross into and possess, a land of hills and valleys, soaks up its water from the rains of heaven.
Torah Temimah points to Bava Basra 19a.
TT lemma: למטר השמים (unit 2 of 2).
English: “From the rain of the heavens.” It was taught: One distances seeds three tefachim from a wall because they cause mildew. Why not simply because of water? The baraita is speaking about the Land of Israel, as it is written of it, “from the rain of the heavens it drinks water.”
Custom (distancing seeds from a wall in Eretz Yisrael)
In a land watered by rain rather than constant irrigation, the harm of seeds near a wall is mildew, not only wetness.