Here we'll talk about when a person has to keep away from his neighbor's property because something he has may damage another item near his neighbor's property. The Mishnah says that a person has to distance his pool of water in which he's soaking his flax from his neighbor's yerek (vegetable patches). Also, a type of herb called cress has to be kept far away from his neighbor's onions, and mustard seed has to be kept away from his neighbor's bees. The first item mentioned in each of these cases causes damage to the second item mentioned. Therefore, the owner of the damaging item has to keep it far away from his neighbor.
When talking about flax pools, the water there, if poured into the ground, will destroy the vegetables under it. It will seep under and destroy the vegetables. Also, cress, this type of herb, will take away the sharp taste of an onion. And mustard seed can't be near the bees because if the bees eat the nectar of the mustard, the honey they produce won't be as tasty. Therefore, the owner of these damaging item has to move the item away from the neighbor's items that we spoke about.
According to Rabbi Yosei, you're allowed to plant mustard seed near bees. According to him, mustard seed doesn't harm bees, but the bees harm the mustard. It's not that there's a problem for the bees if they eat the mustard; it's a problem for the mustard. They destroy the mustard. So the owner of the mustard seed could say, “You don't tell me to keep my mustard seed away. You don't tell me to keep my mustard seed away from the bees. Keep your bees away from my mustard seed.” Therefore, the owner of the mustard seed is not required to move it away. Rather, the owner of the bees has to move the bees away from the mustard seed.