3,381. Tithing Hefker

Hilchos Maaser 1:11

If stored onions sprouted roots next to one another, even if they grew roots in the soil of an attic, they are exempt from maaser. If a landslide covers them and they are exposed to the elements, then it’s as if they were planted in a field and one must take maaser from them.

Hilchos Maaser 1:12

Let’s say that someone was guarding the grapes of his field and someone else comes along and takes the figs that were left in the field, or he was guarding the gourds in his field and someone else came along and took the scattered grapes of his field. If the owner of the field is concerned with the leftover produce, then taking it is stealing and prohibited. In such a case (because the produce is owned), the produce is obligated in terumah and maaser. If the owner of the field doesn’t care about the leftover produce, it’s not theft and one may take them. In such a case (since the produce is considered ownerless), the produce is exempt from tithes.