959. Binding the Species
136:7 A Jew must not cut the four species from the tree for himself, even if he has permission from the owner of the land. Rather, a non-Jew or another Jew should cut them and one should then buy them from him. (If the Jew did cut them for himself, with the land-owner’s permission, they are valid and he may recite the bracha over them – 649:10.)
136:8 One takes three branches of hadassim (myrtle) and two branches of aravos (willow) - one may not add more! - and they are bound together with the lulav to make one bunch. One must make sure that they are arranged the way that they grow, with the place where they were cut below. If even only one is upside-down, then one does not fulfill his obligation, even after the fact. One places the hadassim on the right side of the lulav's spine and the aravos on the left, so that when one takes the lulav with its spine facing him, the hadassim are to his right and the aravos are to his left. (A left-handed person keeps these three species bound the same way a right-handed person would use them – Mishnah Brurah 651:12.) At the bottom, they should all be lined up so that when one takes the lulav, he is grasping all of them. In any case, one must make sure that the hadassim are a little higher than the aravos. One must also make sure that the spine of the lulav is higher than the hadassim by at least a handbreadth (somewhere between 3 and 4 inches).
These two species should be completely bound by two bands, one on top of the other. Aside from this, there should be three bands binding them to the lulav. (The common practice is to make all these bands out of lulav leaves - Mishnah Brurah 651:8.) Only one handbreadth at the top of the lulav should remain unbound so that it will rustle when it is waved. If a string is wound around the hadassim, it must be removed before binding the species together so that it does not form an obstruction between the species. If the binding becomes loose on yom tov, it may not be re-joined on yom tov with a knot, but with a bow or by wrapping around the species and inserting the ends of the bands into the existing loops.