Cool little game!
I feel like this is one of the few games that gets window stacking correctly. In many others I found it hard to manage them how I wanted to, that be moving them around and picking the ones that I wanted, but this one controlled that great. The only improvement I would see for it is that they can sometimes overlap with the hotbar, which can get in the way even if its the only window on the screen.
I liked that there was a flower with some different effects, it shows how this game could introduce many different flowers all giving you some sort of bonus for having / growing them. Although I don't think any of the levels were short enough to make real use of the timer one, it shows good ideas.
It would also be cool to have the flowers behave with their windows a little differently. Maybe there are some flowers that have a high passive generation, but will always be creating windows even if it is fully planted. Or ones that grow quickly, produce a lot of windows, but give a good amount of gold once they are finished.
Having to lose the entire flower if you didn't complete a window in time feels kind of bad, especially when you couldn't get to the window in time because you had 3 other ones to do. It could be made so that it only goes down a stage or freezes for a little while. You could maybe keep losing the entire flower for specific ones that do require perfect maintenance.
If you introduced a few more window styles, (thus maybe a bit more time to do them) I could see this growing out into a larger game easily. You could have some windows for picking off bugs, trimming, cleaning the dirt before planting, etc.
The rate that the windows come at can be kind of controlled, I found that if I planted everything at once they would all appear at the same times. But if I just staggered my planting then they would be very manageable. Maybe introduce some more random elements that make it harder to control knowing when they appear.
Art is clean and simple, and the music is a jam!
Nice work!