I think this idea is beautiful! I definitively would use it for some plants at home. But I'm not buying new plants each month, and even if I do, I don't know if I would use this for all of those. I have only 8 plants I would like to scan and forget, and the idea of subscribing throws me off, even if I can unsubscribe.
A better pricing schema for this, that also combat today's subscription fatigue, would be to sell X amount of plant scans. Like you can sell 10, 30 or 60 in different pricing scales. Pay once, the already scanned plants stay there in the users library. At least, I would find that pricing to be much more realistic and fair, and I suspect plenty of potential users are in the same boat as me. I will be able to personally scan the aforementioned 8 plants today, and 2 new plants in the long run, and it will feel great and fair.