Thanks so much for your kind words! I'm glad you liked how the game looks, we're very proud of the art made for it.
There is no way to stop the infection from spreading forever, but the infection can be slowed down. You can slow it down by watering plants that have already been placed, to make them grow larger (from seed to fully bloomed). By using the ability bound to the 'r' key, you can snip away the infection from the plant. This does also set the plant back one stage, and saplings can't be snipped, so it becomes a bit of a balancing game.
Once again, thank you so much for playing :D