“Some follow the practice of distributing garlic to those present at pidyon ha-ben feast.
Reason: certaine books mentioned the immense spiritual significance of the pidyon ha-ben feast. It is said thet whoever participates in such a reast is considered to have fasted 84 fasts. Bu distributing garlic, a small quantity of which can spice entire potfuls of food, we enable many others “to share” the meal of the pidyon ha-ben”
From book “Rite and Reason. 1050 Jewish Customs and Their Sources” by Shmuel Pinchas Gelbard.