MVP for that will be adding photo of the plant, notes on location, adding name/nickname of the plant, adding watering interval
Nice to have - connect to AI so plant can be recognized by the photo with all information like name and watering interval, placement suggestions coming from wiki or something. At least pulling such information by manual entered plant name without plant recognition from the photo(in case you know the plant name)
Ideal way will be push notifications with onscreen notifications block where u can see plant photo, hint on location, hint on amount of water to fill, plus button to mark as watered which will also dismiss notification
Nice to have smart watch companion
Settings to setup your at home schedule, for example morning evening slots (in case some plants needs water two times a day).
Ability to share plants with family members or neighbours. In this case, every person will get notification on shared plant.
Nice touch will be gamification with stricks - like u have n't missed scheduled watering 10 times in a row, or watered 50 times and so on. Badges, points, maybe using some kind of plant or water related mascot which will grow when u earn points.
One idea is to have main page with list of all plants sorted by the next time of watering, showing this time straight there