I’m looking for the source(s) for the custom to use more than 3 Hadassim with the Lulav. My personal custom is to use 9, and I’ve heard of a custom to use as many as 70! I remember seeing it brought somewhere, but haven’t been able to find it again. (I believe there are also those who say to add Aravos and not Hadassim)
This site writes
It is the Chabad custom to add multiple Haddasim to the standard three, adding at least another three. The greater the number of additional Haddasim, the better.
In Sefer HaMinhagim page 65 it says: 4, 12, 13 or 26 but not 9, 68 or 69.
The Rebbe’s personal custom is to take 36 since 5741. (In 5711 – 13; from 5712 till 5740 – 26).
Nonetheless, as DoubleAA noted above, the Shulchan Aruch OC (651:15) poskins
לא יטול יותר מלולב אחד ואתרוג אחד אבל בערבה והדס מוסיף בה כל מה שירצה
- One should not take more than one lulav and one etrog. However, one can add as many myrtle or willow as they want.