As discussed in this BGG topic, Bishop is one of the most effective counters to a fast Gardens rush strategy. Trashing each Garden nets about 3VP chips, and this accumulation of VP chips discourages the Gardens player from ending the game. Moreover, Bishop’s primary drawback (allowing opponents to trash) is moot against a Gardens opponent. As a result, a Bishop player who consistently buys Gardens to crunch into VPs can keep ahead of the Gardens player, such that the Gardens player is left with an abysmal deck and unable to end the game in light of the Bishop’s VP chips.
The two primary other trash-for-benefit cards, Salvager and Apprentice, also work well as a counter to Gardens, but neither provides the VP chips that discourage the Gardens player from ending the game. Remodel might also work, especially if you can Remodel Gardens into Nobles or Harems. In extreme circumstances, you can simply Chapel the Gardens, but that’s much less of a deterrent to the Gardens player than being able to convert them into 3VP apiece.