A vital part of a Plottie's care is their pot. Plotties need their pot for resting, restoring energy and nourishment. Because Plotties are plants, they need to convert sunlight into energy through the process of photosynthesis. This process can only be achieved if the Plottie is getting enough nutrients from the soil/substrate it sleeps in.
Essential minerals, vitamins and other chemicals are absorbed into the Plottie's skin while it sleeps. When it's low on energy, a Plottie will burrow into the substrate until it is fully rested and fed.
As Plotties mature they may be able to live without their pots: Some of them grow very attached to their pot and will always return to it while others are reluctant to go into it from the moment they sprout out of the soil. However, Plotties who don't sleep in substrate will need to take diet supplements during their whole life to compensate for the lack of nourishment.