The Torah states that the Hadas must be braided. This means that there are three leaves that extend from each area of the branch and that these three leaves are symmetric to each other that they extend from the same horizontal line. If two leaves are symmetric but third leaf grows higher or lower than the other two, it is not considered braided. This form of Hadas is called a Hadas Shoteh and is invalid for use throughout all seven days of Sukkos. It may not be used even in a time of need that no other Hadas is available, even if one desires to take it without blessing.
How many leaves on the Hadas must be Meshulash? Initially it is a Mitzvah to buy a fully Meshulash Hadas. This means that the Hadas should be Meshulash with three symmetric leaves for its entire Shiur of three Tefachim. Nevertheless if the Hadassim are majority Meshulash they may be used even initially with a blessing. This means that if majority of the sets of three leaves coming out of the branch have their stems coming out from the same horizontal line throughout majority of the Shiur of three Tefachim, then the Hadas is valid. [If majority of the Hadas is not Meshulash throughout its Shiur of three Tefach the Hadas is invalid.]
Must majority of the Shiur be Meshulash or majority of the entire branch?
 Kashrus Daled Minim p. 114; Piskeiy Teshuvos 646/6
 Bach; Bechureiy Yaakov
 Peri Megadim; See Biur Halacha 646 Leikuva