When it comes to plants, I'm good at exactly one thing: killing them.
There's a small tree on my desk right now while I'm writing this that I just noticed is covered in a little bit of dust and I don't think has been watered in… a month? Maybe more. And I look at this thing EVERY. DAY.
Waterbug is an app for people like me who can't seem to get their plant care under control but still want to own plants. With the app, you snap a picture of your houseplants and then set a watering schedule for them.
For instance, this guy on my desk doesn't need to be watered every day, but he'd probably enjoy some water once a week. If you're not really sure when you're supposed to water what you have (clearly I don't), then there's also a library of plant care tips to help you figure out everything from when and how much to water it to how to prune it or handle pest control.
Once you've set up a schedule, the app will remind you to water specific plants when it's time to do so. After you let the app know you've done your job, then the timer will reset for the next watering (so if I'm three days late I don't end up overwatering my green friend when his original scheduled watering comes up).
It's really similar in idea to all those trackers that were popular a few years ago that you physically put in the pot with your plant, except this one doesn't have any hardware involved except your phone.
All that knowledge will cost you. The iOS-only app is currently $4.49 in the App Store. If you want something silly but don't have the cash to spare, Planty offers some of the same water-tracking features without the plant-specific knowledge built in.