Thanks for the feedback, was one of the coders/level designer. We had an awesome person for both Art(Get More Cabbage) and music (charlstothe).
Unfortunately we had to finish the shop at the last minute. You should be able to buy all the upgrades normally but they don't actually take your money properly. You don't know if it worked visually until you go to play the level. There also isn't a visual indication when you have the max upgrade.
I did notice the issues with the flowers being difficult to avoid or hit at times, if I had a little more time I would've made some adjustments to balance that out a bit more.
Thanks again for the feedback.