A solid prototype! What you have now is a good foundation to add your unique mechanics later. The only other basic mechanic I would add would be to replace towers - right now you can only plant one and that pot is locked in as a cactus/pumpkin. I assume once more plant types are added I would want to delete the cheaper, weaker towers.
I also want to compliment the relaxed vibe compared to other tower defense games; usually there's a million particle effects and sounds. The music is relaxing and the garden aesthetic makes me feel like a kid messing around in the backyard. I look forward to seeing future updates!
My intention was to let it be available as a browser game from the start, but the build wasn't running on the browser so I had to quickly scramble to submit the downloadable versions. Yeah, I will make sure it builds right on the web before I try to upload it again, but it isn't the focus right now.