You’ll need lots of pollen to level up your moths, and this will come from the Pollen Flowers you discover as you expand your environment. Setting shifts will cost coins, the more pollen you want to produce, the more coins it will cost. Tap on flowers to set “shifts” of pollen production, then come back when your flowers are ready to pop and open in a flurry of valuable pollen.
To keep your game running smoothly, there's a limit to how much pollen you can have sitting around in your forest at one time. You can see your progress toward this limit on the Make Pollen screen that pops up after tapping a Pollen Flower. If you've hit your pollen limit, it will show in red and you'll need to feed some to your moths before you can make more.