This game consists of 12 achievements.

In order to unlock an achievement, you will have to unlock and use a flower. Unlocking and using all the different flowers will grant you 100% completion.
To unlock flowers you will need to gain points.

You can get points very easily. Just select the basic pot (0 Points). Then put as many flowers as you want to into the pot. More flowers = More points.

For example:
If you use the basic pot (0 Points) and the basic flower (0 points). And you put 15 of those flowers into the pot and sell it, you will gain 15 points.

Better flowers that cost more points will grant you more points as well. Just keep putting a lot of flowers into a pot, sell them, gain points and unlock all the flowers!

Goodluck.