Avodah Zarah, Chapter Three, Mishnah Eight
This mishnah talks about using the space underneath the asherah tree. The question asked is: is using this space considered deriving benefit from idolatry and therefore forbidden? Furthermore the mishnah discusses the purity of one who passes underneath the asherah tree.
1) One may not sit in its shadow, but if he sat he is pure.
a) Nor may he pass beneath it, and if he passed he is impure.
2) If it encroaches upon the public road and he passed beneath he is pure.
3) They may sow vegetables beneath it in winter but not in summer, and lettuce neither in summer nor winter.
a) Rabbi Jose says: even vegetables [may not be planted] in winter because the foliage falls upon them and becomes manure for them.
Section one: One is not allowed to sit in the shade of an asherah, for by doing so he would be benefiting from an idolatrous object. However, sitting in its shade alone will not cause him to be made impure, because he did not actually sit underneath the tree. He is not allowed to pass under the asherah, and if he does he is impure. According to the Talmud this is because we assume that underneath the asherah thee is an idolatrous offering, which causes Jews to become impure. When the branches of the tree form a tent over the person and the idolatrous offering the impurity of the idolatrous offering is transferred to the person (this is called tent impurity).
Section two: If the asherah was leaning over onto the public road and a person passed underneath it, he is not impure. The impurity of the asherah is only rabbinically ordained, and in this case the Rabbis did not decree that one who walks underneath the asherah is made impure. The reason for this is that the Rabbis declared idolatrous objects to be transmitters of impurity in order to keep people away from them. Since this person who was walking on the public could not have avoided the tree, he is not impure.
Section three: In the winter one is allowed to sow plants underneath the asherah tree, since the shade provided by the tree will not benefit the plants. In this case he is not benefiting from an idolatrous object. However, he may not plant lettuce underneath the asherah, even in the winter, since shade is always beneficial to lettuce.
Rabbi Yose states that even vegetables may not be planted in winter, since the falling leaves will act as manure for the vegetables and therefore the planter would be benefiting from an idolatrous object. In other words, although he will not benefit from the shade since he will benefit in other ways, it is forbidden.