136:1 It is already the practice for one who buys an esrog and a lulav, if he is not familiar with the laws, to show them to a rabbi who can determine whether or not they are fit for use. This is because there are many detailed laws involved. One should try to buy a fresh lulav because a dry lulav (one whose spine or the majority of whose leaves have gone dry – OC 645:5) is only fit for use in an emergency. Some say that a lulav is considered dry if its greenness is gone. (This is the majority position so one should not act leniently in this matter so long as a fresh alternative exists – Mishnah Brurah 645:25, 649:58.) The minimum required length of a lulav is that its spine is four hand-breadths – about 13-14 inches), not including its upper leaves. In a case of compelling need, the length can be 13 and one-third thumb-breadths (more like 10.5-12.5 inches).
136:2 The hadassim (myrtle) must be three-leaved, meaning that three leaves extend from every stem in a single row. A leaf may not be higher or lower than its adjacent leaf. The leaves must cover the stalk, meaning that the top of each leaf must come over the stem of the leaf above it. It’s hard to find kosher hadassim among those that are imported, so they must be checked. A diligent person should try to buy hadassim that are fresh, green, three-leaved and beautiful. It’s better that they be grown domestically but one must make sure that they are not grafted, nor were they grown in a pot without a hole in the bottom. (If one knows they were grafted, they may not be used. If one has no idea, he need not be concerned as most hadassim are not grafted – MB 648:65.) One must be similarly scrupulous when it comes to domestically-grown lulavs. If one cannot find three-leaved hadassim, he can use hadassim that aren’t three-leaved but then he cannot recite the bracha.