The plant greenhouse (https://legacy.atrocity-pets.com/croplevelup/greenhouse) can be located under the exploration menu. Here is where you can water plants that you or other users planted.
(https://legacy.atrocity-pets.com/picuploads/farming/garden/gardenplantday2.png)
(https://legacy.atrocity-pets.com/picuploads/farming/greenhousenpcsimma.png)