My Little Shop of Horrors - S1.E8

Principal Celestia leaves Twilight Sparkle and Spike in charge of tending to her garden while she's on vacation. Unbeknownst to Twilight, some Equestrian magic enchants her watering can. As Twilight begins watering and singing to the plants, the plants start to grow and come to life, singing along to Twilight's song. As Twilight gives them more and more water, the singing plants become increasingly aggressive and demand more. Twilight sends an SOS text to Applejack, and when she arrives, she turns on the sprinklers to turn the plants back to normal. Just then, Celestia returns and warns Twilight not to over-water the plants.