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In reference to the triple-leaved hadas the Torah states "a thickly-leaved branch." Its leaves hide its stem, and the leaves grow in a formation along the stem, with clusters of three parallel leaves growing, each from its own petiole, around the stem at short intervals.
Which Hadasim are best?
- It is best to choose hadasim that have many leaves close together so that the stem is completely covered by the leaves. 
How big are the leaves of Hadasim?
- The individual leaves of the hadasim should be approximately the size of the thumbnail. Some Poskim rule that if a hadas has large, wide leaves it is a hadas shote and is invalid for the performance of the mitzvah. 
Does a severed tip of a hadas invalidate it?
- If the tip of the stem of the hadas was broken or cut off it is still kosher and one may recite the beracha over it. Nevertheless, it is best that hadasim have their tips intact. 
What is the minimum length of a hadas?
- According to Maran, a hadas must be at least three Tefachim or 20 centimeters long. However, other poskim maintain that the minimum length of a hadas is 24 centimeters. It is recommended that one choose hadasim that are at least 24 centimeters long in order to fulfill the mitzvah according to all poskim. 
What if the leaves of the hadasim are dry?
- If most of the leaves of someone's hadasim have become completely dry but at least one set of three leaves at the top of each hadas is still fresh, the hadasim are still kosher. 
What if the leaves of the hadasim have withered?
- If the leaves of the hadasim have withered, the hadasim are still kosher. 
- Rambam (7:7) and Shulchan Aruch (651:1) rule in accordance with Rabbi Yishmael, who requires three hadasim and two aravot. The Rama adds that in extenuating circumstances, one may use just one hadas. Regarding their sizes, Shulchan Aruch (650:1) rules like Tosfot that the minimum size for both hadasim and aravot is 10 etzba’ot; however, he also mentions the Rif’s opinion of 12 etzba’ot (see note 3).
- The Gemara (32b) considers a hadas with rows of two leaves and one leaf on top to be a hadas shoteh, or “unstable” hadas. The Gemara understands the requirement for rows of three leaves (meshulashim) to be the explanation of “avot,” the Torah’s description of the hadas.
- Halichot Shlomo ( Ibid.) rules that the determining factor for meshulashim is the location of the stems of the leaves. Additionally, he explains that a row of leaves is considered meshulash if the three stems are in close proximity such that it would be possible to draw a horizontal circumference of the branch that would intersect with all three stems (see diagram). Rav Yigal Ariel (Techumin 11:177) understands that it is sufficient if the leaves are roughly in rows of three and do not blatantly deviate from rows. Rav Chaim Jachter ( Ibid.) notes that the common practice of some gedolim was to analyze the hadas at arm’s length to make this determination. Yalkut Yosef (646:8) rules that ideally the leaves should cover the entire branch.
- The Rama (646:3) quotes a minhag to be lenient if there are two leaves above another two leaves, though the Mishna Brurah (646:15) rules that one should ideally not rely on this minhag. Yalkut Yosef (646:2) writes that such a hadas is invalid.
- Shulchan Aruch (646:5) rules that one ideally should have the leaves be in rows of three for the entire length of the hadas; nevertheless, one fulfills his obligation if the leaves are in rows of three for the majority of the branch. Mishna Brurah (646:18) states that this majority refers to a majority of the minimum size of a hadas branch. Thus, since the hadas should be 12 etzba’ot, a majority would only require no more than 6 etzba’ot, even if the hadas is larger than its necessary 12 etzba’ot.
- If only two leaves remain in each row for a majority of the hadas, Mishna Brurah ( Ibid.) rules that one may be lenient in extenuating circumstances.
- Shulchan Aruch (646:7) explains that for the leaves to be considered dry, they must have turned white. Mishna Brurah (646:20) notes that if they have turned white, they certainly will wither when touched. If it is difficult to determine whether one’s hadas is dry, Mishna Brurah says that one can test it by putting it in water for a day or two and checking to see if it returns to its initial moist state. Shulchan Aruch (646:8) notes that if three moist leaves remain in a row at the top of the hadas, the hadas is valid. Mishna Brurah (646:21) explains that having three leaves on top allows the hadas to retain its status of hadar.
- Shulchan Aruch 646:2
- Yalkut Yosef, Siman 646, Seif 3. Givat Shaul, Yerushalayim: HaKeter Institute, 2010.
- Yalkut Yosef, Siman 646, Seif 4. Givat Shaul, Yerushalayim: HaKeter Institute, 2010.
- Yalkut Yosef, Siman 646, Seif 5. Givat Shaul, Yerushalayim: HaKeter Institute, 2010.
- Yalkut Yosef, Siman 646, Seif 7. Givat Shaul, Yerushalayim: HaKeter Institute, 2010.
- Yalkut Yosef, Siman 646, Seif 13. Givat Shaul, Yerushalayim: HaKeter Institute, 2010.
- Yalkut Yosef, Siman 646, Seif 14. Givat Shaul, Yerushalayim: HaKeter Institute, 2010.