No one knows how, but it somehow became a tradition. Whenever a new pillar inhabited the water estate, they'd add a new edition to the garden. These came in a wide variety, ranging from large floral bushes, to carnivorous plants, to simple garden decor. At midnight, when the moon was high at the sky's peak, they wrote in the abandoned journal of the very first water pillar, detailing what they added, why, and how to take care of it. Tomioka Giyuu never took part in the tradition, but he did add a peach tree in a small grass clearing of the garden. (Cross-posted on ao3)

After Rengoku dies in the battle with Akaza, Senjuro is devastated. So he decides to take matters in his own hands to become the next flame hashira