It's cute and fun and I really enjoyed it. For a first game, it actually kept my attention for the whole five minutes. The only two things I can think of would be 1) text popups to show what was selected (took me about 20 seconds to realize what exactly I had selected) and 2) some slight variation in the timing.
Once I got to the 4x4 field it was pretty much just following the mouse pattern I watered things in. If it was any longer than five minutes it would probably start to get rote.
I kinda disagree with the person who said it's not in the spirit of a one-button because it's essentially a plate spinning game with a farming theme. The focus isn't necessarily on the farming but constantly moving around to get things done before plants die. Good job!