Go for it! I accomplished that last year, by keeping a chart of what was left to grow and what I had planted. Anytime a mii arrived wearing a needed colour, I'd have them plant a few seeds and store them for later. It also helps to only invite 1 mii at a time when you're growing them. It'll take a bit longer, but you'll save lots of Play Coins since you'll water your own flower once each time.