Not open source but I use Planta for watering reminders/tracking.

I recently found out about the Seek app on android - it can id plants using your camera. Useful for figuring out rando unlabeled plants on sale at my grocery store 🪴

Often finding precise information for light values is quite hard, so I use those 3 websites: https://growlightmeter.com/light-requirements-for-plants/ https://plantlightdb.com/?q= https://www.houseplantjournal.com/bright-indirect-light-requirements-by-plant/ (Scroll down)

They don't always agree but they are a good starting point.

My husband and I use a spreadsheet. It has a picture of the plant, information on care I pull from the web (so many great plant care sites around!) and a bit of info on when it was watered last and when last fertilised etc.

We have a large collection but the spreadsheet is still easily manageable.

I'm interested to see if there are any good FOSS options! I've used planta a bit but it has limited features on the free version and I do not need yet another paid subscription.

I regularly employ the use of biodiversity data like SEINet to crossref with herbarium specimens. Honorable mention to the North American Ethnobotany Database for pulling up bibliographic info on plant-human interactions. There's also a tool to lookup collection site IDs for cacti and succulents here: BCSS Field No. Lookup. These aren't necessarily in the realm of plant care but I believe they could make a nice additon to the sidebar. Cheers!

https://github.com/MDeLuise/plant-it

https://github.com/danielbrendel/hortusfox-web