Bubotuber pus was highly corrosive to human skin, so dragon-hide gloves had to be worn when squeezing the pustules.
Forest Trolls used them as a food source, but they did not eat them raw. They washed them in water, boiled them in pots, and added other seasonings. That was where the trouble lay.
There was a lake in the Forbidden Forest that served as a shared water source. Animals from the forest and Centaurs often came there to collect water. When the Trolls washed Bubotubers there, it aroused the Centaurs' intense dissatisfaction. Later, the Trolls even began preventing the Centaurs from drawing water there. At one point, a young Centaur had nearly come to blows with them.
Though it appeared to be a dispute over water, resentment had been building up for a long time. Grubbly-Plank and Apulia Moore from the Centaur Liaison Office were handling the matter.
If both sides found out that Hogwarts had opened a vegetable garden in the Forbidden Forest, it would spark further disputes. So it could only be done in secret. After seeing the students off, Hagrid met them by the Black Lake. He had cast a Concealment Charm over the garden; without the Tree Monkey Frog markers, even he might not have been able to find it himself.
Fertilizer promoted growth, but too much could not be used at once. Though plants could not make sounds—aside from Biting Vines—they still expressed discomfort in other ways, such as yellowing leaves and rotting roots.
If there was only a little too much, it could be diluted with water. But if too much had been added, dilution would not work well, and the soil had to be replaced. When repotting Mandrakes, the new pots had to be prepared with soil suited to their growth. Pomona preferred