One should not sit in its shade, but if he sat, he remains tahor. He should not pass under it, and if he did pass, he is tamei. [If] it encroached upon the public and one passed beneath it, he is tahor.  It is permitted to plant vegetables beneath it in the winter, but not in the summer; and lettuce, neither in the summer nor in the winter. R’ Yose says: [He may] not [plant] vegetables even in the winter, because the foliage falls upon them and becomes fertilizer for them.